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When does polyneuritis equi (PNE) begin in a horse? A polyneuropathy manifests in a horse that is susceptible to the disease.  Which horses are susceptible? Horses that are particularly “inflammatory” or a horse that is allergic to vaccines, even a horse with endocrine issues.  Some horses that contract a virus can succumb.  Once typical signs are present, the disease can be recognized.  But what about the pre-symptomatic phase, what does that look like in a horse with PNE? 

Biomarkers could identify the earliest stage of PNE, if one were looking. At this stage the horse doesn’t have any outward appearance that there is anything wrong, and if you could ask, the horse would agree, all is well.  At this phase it is entirely possible the horse clears the inflammatory issue, probably most of them do regain health and that is why this disease is so rare.

A few horses will start to show early signs of polyneuritis and these signs can be detected, although they are often attributed to other causes-like protozoal infections, EPM. The signs can be so subtle that an owner feels like there is something wrong but they can’t quite put a finger on it.  In human disease the period between possible symptoms/signs and definite symptoms/signs is called prodromal.  Once there is “phenoconversion” and the horse leaves the prodromal phase then enters the symptomatic phase, it isn’t hard to recognize the clinical presentation as PNE.

What is the duration of the sub-clinical phase of disease, the disease is present but there aren’t any outward signs? Polyneuritis equi is a rare neuromuscular disease that is difficult to recognize in the field even when clinical signs are present.  We think a field diagnosis is difficult because it isn’t a disease that is forefront on a clinicians differential diagnostic list.  As in other neurological disease syndromes, ones choice of descriptions has shaped concepts and paradigms in PNE-and that is that the disease is untreatable. Our work concentrates in early diagnosis and treatment options for horses with PNE because this is the meerkattime that damage isn’t permanent and the horse can be returned to normal. Veterinary training and the literature describe end-stage disease. Unfortunately, little can be done in the late stages, hence the grim prognosis and current recommendation of euthanasia.

It is our hope to change the way clinicians think about and diagnose PNE; that would change the paradigm.  It would change the outcome. Paradigm-changing is a step-wise process.  We spent years getting our ideas and research studies completed.  Now we will complete a clinical effectiveness trial on horses recognized with PNE, and many of these will be end-stage.  The study will allow us to collect effectiveness data and define biomarkers to detect treatable disease.  The goal is to use biomarkers in a second effectiveness study.  All the data will help us get answers to more questions. Can there be a genetic pre-disposition to disease?  Is disease caused by a specific virus or microbial agent?  Is it possible that environmental exposure to an “agent” is the inciting cause?  A useful strategy to study PNE is to define a population of horses that have a high likelihood of developing PNE.  can we define that population? You see, to change what’s ahead one has to continually look in a different direction. 

We will be sending out requests to veterinarians and owners that have cases suitable for our effectiveness field trial.  There are some criteria that make sure the horse can be included in the trial.  We can answer questions for you, if you think you have a horse with PNE. We will provide study medications at no cost and we will pay for some of the pre-entrance testing.  We need you to help us change the PNE paradigm.


blogger-image--213779556If you search the literature you will quickly realize that polyneuritis equi (PNE) has a grim prognosis. The prognosis is poor because there are no recognized treatments. Only palliative care and euthanasia are offered as the standard of care for the PNE horse.  It is our goal to change that with our Hope Initiative.

We began to recognize a pattern in horses with neuromuscular disease and a literature search led us to papers published in the 1980’s.   One paper authored by Fordyce gave specific signs used to evaluate horses with putative PNE and led to the Fordyce Score.  We found quite a bit of research done  in horses relating to PNE. The disease is rare and presents clinically with diffuse involvement of extradural nerve roots of multiple peripheral nerves. The pathology is a polyneuropathy characterized by  inflammation  and demyelination.  PNE has no known single cause.   The inflammatory process may initiate primary or secondary demyelination of nerves by a “bystander mechanism” where any antigen that reaches the peripheral nervous system attracts and activates lymphocytes and macrophages.  We’ve reviewed the topic for you in our eBook Polyneuritis explained, available on Amazon for $4.99. The disease may be reversed if it is caught early and remyelination of the nerves can restore function.

A spectrum of signs can be recognized in PNE-horses and careful case analysis gave us the heads-up that treatment may be initiated before chronic demyelination progressed to end-stage disease.  That’s when  we knew that a horse can recover from PNE.  We were surprised to find that the literature described a diagnostic test for myelin protein antibodies many years ago.  The presence of these antibodies were related to disease.  The molecular structure of myelin was determined and the immune-mediated process was determined experimentally in animals.  Some tweaks in the diagnostic protocol were needed, using a recombinant protein avoided non-specificity issues and folding  the protein into its native state was necessary to make the test useful.  Finally, epitope mapping was highly illuminating to understand the pathogenesis of disease.

We’re developing a  licensed treatment.  Our  next step  is a field effectiveness study.  A (any breed) horse that is between 2 and 30 years old , 605-2420 pounds and shows signs of PNE with a Fordyce score of 4 is considered eligible.  There are some other restrictions, and qualification to receive medication is made on a case-by-case basis. Some testing is required, horses need to be negative for sarcocystosis by serum analysis and the possibility of trauma is ruled out by examination, history, or radiography.  Your  veterinarian can use endoscopic exam or radiographs to rule out osteoarthropathy. Vaccinations must be current (within a year) and include rabies, EEE, WEE, and WNV. Of course, before starting any medications a serum chemistry and CBC should be done.

Some of the other qualifications are: the horse is expected to be manageable and cooperative with handling, examinations, and the owner is able to give medications daily.  The study involves a two week treatment and two clinical examinations made by your veterinarian.  The owner will need to fill out a  checklist each day the horse receives the medication and this checklist is how we evaluate the response to treatment.  If you are unsure that  your horse qualifies based on the clinical signs you are seeing, you can email us or use the following  links, answer some questions, and we’ll get back to you.

You may already know, based on your experience, that your horse shows signs of PNE, or your veterinarian has made the diagnosis. This link is useful to determine the Fordyce score and eligibility for the study:

You or someone you know may love a horse suffering from PNE, tell them to contact us and join our Initiative to give hope to horses suffering with PNE.  blogger-image-702499765

Scoring systems are useful to evaluate humans and animals.  The well known APGAR score is a test given to newborns soon after birth.  This test checks a baby’s heart rate, muscle tone, and other signs to see if extra medical care is needed.  The test is given at one minute after birth and again five minutes after birth. Another well known scoring system is the Mayhew Score, or more often the “Modified Mayhew Score”, that is intended to evaluate horses for equine protozoal myeloencephalitis.  The Mayhew Score differentiates upper motor neuron diseases from lower motor neuron diseases using an extensive neurological examination.  The scoring system allows the clinician to form a differential diagnosis list. Scoring systems are generally named for the author of the system.

The Fordyce Score is a system described by Fordyce, Edington, Bridges, Wright, and Edwards in 1987 that was designed to evaluate horses with cauda equina neuritis (polyneuritis equi, PNE) and differentiate PNE from other equine neuropathies by ELISA.

Polyneuritis equi is a condition with some specific characteristics that are paralysis of the tail, bladder, rectum and the anal and urethra sphincters, accompanied by an area of analgesia (loss of response to stimulus)  around the perineal region.  Muscle wasting is common over the hindquarters and the horse can have an uneven gait. Cranial nerves can be involved and characterized by a drooping lip and ears, inability to blink and atrophy of chewing muscles, although signs can involve other cranial nerves as well.

Because the pathology of PNE is inflammation of the nerve roots that form the cauda equina and any other peripheral nerves that are involved, it was common to examine affected nerves by histopathology.  Histopathology was used because horses were not diagnosed until late stage disease and euthanasia was the recommendation. The Fordyce team recognized that antibody against the animals own myelin protein could be measured pre-mortem using an ELISA test.  The first scientists to recognize that there were circulating antimyelin protein antibodies in experimental allergic neuritis in rats, was the Kadlubowski Group in 1980.  And in 1981, they recognized the same condition in horses with PNE.

Molecular techniques in the 1990’s allowed researchers to refine the antigens used to analyze serum samples.  This was important because laboratories that used a crude mix of myelin protein from horse spinal nerve tissues in their assays got varied results. The P2 myelin protein is the required  molecule and then it needs to be presented in its native form.  Rostami and Gregorian mapped the myelin P2 protein epitopes (short amino acid sequences that are reactive to the immune system) and showed that a small piece (peptide) of the protein caused an autoimmune reaction that appeared later in the course of disease.  The difference between the whole P2 protein antibody reaction and the peptide antibody reaction was that animals became refractory; they stopped responding to the epitopes on the whole P2 protein.  They stopped responding even when clinical disease was apparent.  Yet if the peptide was stimulating the animals’ immune system, they did not become refractory.

The animal isn’t a bystander in this disease.  The horse will heal the peripheral nerves because the cells that lay down more myelin (Schwann cells) are not compromised.  It is the degree of inflammation that can get out of control in late, irreversible disease.  In chronic disease the horse will heal (scar) the damaged nerves using fibrosis or calcium.  These healed nerves can’t conduct messages to the muscles that they innervate.  As the myelin is sequestered from the immune system the anti-myelin protein antibodies fade from disuse. This leaves the horse with end stage disease.  Thus there is a progression of anti P2 antibodies in the serum.  There will be no antibodies early in disease, as disease progresses antibodies are present, and finally, antibodies are absent in late disease due to the healing process.

Another IMG_0550reason for inconsistent assay results from some researchers was the selection of cases.  Because cases selected for study were end-stage it would not be expected that all horses would be seropositive on their ELISA assay.  A more uniform selection of cases can lend validity to the anti-myelin P2 serum assay and Fordyce was the first researcher to do this.  Fordyce clinically assessed animals for PNE giving one point to each of the following signs: tail paralysis, urine drippling, rectal dysfunction, perineal analgesia, muscle wastage over the hindquarters and any sign associated with a cranial nerve neuropathy, ear droop, inability to blink and masticatory muscle wastage (see picture). Fordyce considered a score of 4 or greater was consistent with PNE. Fordyce correlated 12 of 14 seropositive cases  (titer at 1 to 8) that were considered to have PNE based on clinical score and/or post mortem criteria .  These were gold standard cases. One horse had shivers and seroconverted to negative after 5 months. Thirteen horses with non-PNE neuropathies and 20 control negative sera were seronegative on the assay. Fordyce concluded that the presence of antibody to P2 in horses suffering from PNE is useful as a diagnostic for PNE.

We agree with Fordyce and have fine-tuned the anti-myelin protein P2 assay (MP2)  to include that small peptide (myelin protein 2 peptide, MPP) discovered a few years after his work was published. We believe that the value of a combined assay (MP2 and MPP) will allow us to measure the duration of the condition, if not the severity. The advantage to a diagnostic test is recognizing disease before it is late stage and irreversible. A diagnostic test will enable researchers to find effective treatments.  Let us know how you find the utility of the Fordyce Score system in your evaluation of equine neuropathies.  Call us to find out more about serum testing in these cases.

Some diseases are easy to spot. Unique clinical signs can be directly associated with disease, skin fungus for example. It’s hard to ignore your horse when he squints a tearing and swollen eye, those are hallmark signs of a painful corneal ulcer! Fortunately, some diseases have definitive tests.

There are also diseases that aren’t so easily recognize. The veterinarian makes a diagnosis by evaluating the clinical signs and narrowing down the possible disease list with an array of laboratory testing. Yet, some difficult-to-diagnose diseases don’t have definitive tests to get them onto or off the differential diagnosis list.

What can make the definitive diagnosis of some diseases elusive is a fundamental principle: the body reacts to multiple insults by using a few selective, well differentiated pathways. Innate immunity is a quick, generic response system and is a first line of defense against infections. A more refined, specific, and later developing response is called adaptive immunity. An adaptive response results in specific antibody molecules and sensitized T-cells that are “trained” to recognize a distinct infectious agent. Innate immune responses are non-specific and common to infections while adaptive immune responses are the bodies red flags that may used for a definitive diagnosis.

We are going to explain why polyneuritis equi, that is primarily a dysfunction of the inflammatory response system, can be difficult to recognize. To understand PNE, one must have a brief understanding of how inflammation causes clinical signs.

In polyneuritis the thing that is different is that the immune system is now attacking something it shouldn’t. The first step in the immune process is the inflammatory response. Inflammation is a very early response. Even though it is very early it is possible to pick up some nonspecific inflammatory elements in a blood sample. In the PNE disease process abnormal values are associated with subclinical signs. Subclinical means that the signs are generally too subtle to be picked up on a physical exam.

It is important for the body to react quickly to infections. Rapid reactions employed by the innate immune system require communication between several first responding cells to the infection. The blood stream serves as a rapid transit system for the First Responders that are white blood cells (WBC) in innate immunity. These circulating cells are trained in surveillance and at the first encounter with foreign entities they sound the alarm. The signals they use are cytokines. Cytokines are chemicals that exert an effect on individual cells and sometimes on tissues.

The immune system is very economical. Sometimes cytokines turn things off and sometimes cytokines turn things on. Cytokines can turn one pathway in a cell on and at the same time turn off a pathway in the same cell. Think of a switching station along a railroad, pulling one lever changes the destination of the train to a meeting in New York or a party in Florida. Knowing when to pull the lever is important and that is context. Cytokines receive context from other reactions and other cells that let the immune response know where the party is happening.

Innate immune (early and quick) reactions start with inflammation. The five hallmark signs of inflammation are heat, pain, redness, swelling, and loss of function. These signs occur on a large, gross, as well as a microscopic or cellular level. The current discussion focuses on cellular reactions responsible for the gross signs seen in the horse. Inflammation yields changes in measurable clinical laboratory values that may help with a diagnosis of inflammation. Remember that these early, acute reactions are not specific to a specific disease but the response to infection.

Initially, subtle microscopic changes set in motion by cytokines have no outward effect on the horse. The effect is sub-clinical. Yet the ability to measure very minute amounts (or in some cases changes in amounts) of cytokines are accomplished in the laboratory. As the effects of cytokine reactions progress to larger areas of tissues the clinical signs will be noticeable in the horse.

Horses with PNE usually have normal WBC counts. Testing for specific antibodies against bacteria and protozoa will often be negative. Antibody against myelin P2 protein can be absent (early) or present (during fulminant disease). The following discussion will explain why when you test and the context of testing are important for diagnosis and perhaps prognosis of PNE.

End-stage disease, when a horse is beyond help, is where the current recognition of PNE stands. We want to change that. Late in disease, a transrectal ultrasound scan may show swelling of the sacral nerves as they exit the ventral sacral foramina. A biopsy of the sacrocaudalis dorsalis lateralis muscle was useful in one published case. In this case, the horse had no feeling in the tail (clinical signs were paresis or paralysis of the tail and decreased sensitivity). A biopsy showed that WBC’s had infiltrated the tissues and obliterated the nerve structure, but not the muscle fibers. Even in this end-stage case an attempt at healing myelin was observed. In some areas that were examined under the microscope, there was new myelin but in other areas, damaged nerves were covered with fibrotic tissue, the process of fibrosis.

Fibrosis is interesting, it is the body’s attempt to cover nerves that have lost nerve-insulating myelin due to chronic inflammation. The body can remyelinate nerves if inflammation is turned off, but if the repair process is thwarted by chronic inflammation, fibrosis takes over. Myelin allows rapid conduction of messages through the nerve whereas fibrin does not. The clinical signs will not respond to any treatment in late-stage disease when nerves are fibrosed. The antibody response to myelin may be absent because the reactive areas of the nerve are covered by fibrosis. The net results is a horse may produce an overabundant amount of granulation tissue that potentiates instead of controls the inflammatory reaction.

Observing remyelination in the presence of inflammation is good news, if fibrosis hasn’t occurred. Depressing the initial inflammatory reaction may reverse the clinical signs of disease. The propensity of the horse to have inflammation may be an anatomical difference in this species because horses have significantly more myelin P2 than other species.

A more in-depth view of the process of disease rests in the type of cells that are responding. Inflammatory T-cells and antibody producing cells (CD20+) infiltrate the damaged neural tissues. The infiltrating cells are macrophages (CD11a+ and c+), immunoreactive CD8+, cytotoxic T-lymphocytes, and a few CD4+ helper T-lymphocytes and CD3+ T-cells.

The bottom line is histopathology supports an adaptive immune response to inflammation caused by virus, chronic protozoal exposure, rickettsial infections, and immune-mediated diseases. We’re not the first ones to ask if PNE is a result of multiple etiologies that set the immune system into motion via common pathways.

PNE was described in the literature (medical books and journals) a long time ago. There are other things that can look like PNE to the clinician examining a horse with neurologic deficits. Many of the published reports were written before the development of the sensitive molecular tools we have today. There were no diagnostic tools to differentiate PNE from some of the other causes of neuromuscular disease. This meant the reports sometimes muddled the various findings. This in no way means the reports weren’t good, they were. The books and the papers are not wrong, they’re just outdated or incomplete. They don’t include the precision with which we can define the disease today. Still, a lot of their findings are valuable. Remember that PNE had no cure and it was often diagnosed late in the disease process. The changes were end stage disease that were found by microscopic examination after an animal was destroyed.

Some published reports cite the involvement of tissues encasing the cerebellum and cerebral hemispheres, although most agree the disease involves the peripheral nervous system and not the central nervous system. In chronic PNE the branches of trigeminal nerves show lesions, again infiltration by inflammatory cells and perineural fibrosis. The spinal column can show reddening and swelling with peridural edema. Lymphocytic infiltrations can be present in various nerves, the femoral nerve or cranial nerves. Horses with long-term disease can also have calcification of spinal nerve roots and extensive perineural fat. The results of these lesions are paresis or paralysis, sensitivity, muscle wasting, gait anomalies, tripping, and dropping feed.

When researchers attempted to find the causes of PNE, it was difficult. It’s a rare disease. They looked for infections and signs of trauma. Recall that in the past, at the time of diagnosis, PNE was already advanced. If there was an infection that started the process, that infection was already cleared by the immune system, long before the late signs of PNE appeared. There are other causes of nerve demyelination. Since PNE is the result of the immune response, it doesn’t matter too much what sets innate immunity into motion. It matters that the immune system has “seen” the myelin and now sets out to destroy it.

Normally reactive myelin P2 exists inside the Schwann cells membrane. The macrophages (white blood cells) exist in the blood. The myelin P2 is not exposed to the blood stream, so the immune system doesn’t know it is there. That’s the way it is supposed to work. What can happen, though, is that there’s a disruption in the normal Schwann cells integrity and the myelin P2 is exposed to the bloodstream resulting in inflammation. Let me digress for a moment.

There are speculations as to the etiology of polyneuritis equi. The problem is that the disease isn’t reproduceable using organisms or trauma. By the time chronic inflammation sets in the body has exterminated the organisms sometimes leaving only the residual antibody responses.

Polyneuritis equi is a primary demyelination disease. Primary demyelination can occur without inflammation, this can occur in lead poisoning. Primary demyelination can occur with inflammation where the inflammatory cells are mainly lymphocytes and macrophages. Inflammatory demyelination is thought to have an autoimmune pathogenesis, but the reaction isn’t necessarily against “self”. We discussed the up-regulation of certain antibody binding areas on myelin P2 as a response to T-cell stimulation in another section.

It was proposed that antigens, or “self”-proteins that reach the peripheral nervous system attract and activate lymphocytes and macrophages. These cells become a nonspecific cause of a primary or even secondary demyelination. This is called a “bystander” mechanism. Finding an infectious cause of PNE is unexpected in this scenario.

It is apparent from the discussion that two processes may be at play. There is an innate immune response that is a quick inflammatory defense against infections. The infection can be a bacterium, a virus, or a protozoan. After the acute phase reaction, the body equilibrates, and the cytokines facilitate a robust adaptive immune response. Normally, acute inflammation switches off while an adaptive reaction is switched on, a cytokine success.

Occasionally the acute inflammatory reaction doesn’t turn off. It becomes dysregulated. The cytokines forget context and keep the acute reaction in play. The reaction becomes chronic. The cytokines and their end-products keep the reactions going in an endless cycle. As chronic inflammation (T-cells) continue to destroy myelin an adaptive reaction against “self”-myelin ensues. At this point anti-myelin P2 antibodies are measurable.

It is important to recognize where in the cycle the disease is manifesting. We do that by measuring an acute phase cytokine, C reactive protein (CRP), and adaptive reactions against two areas of myelin P2. The cytokine CRP is one “turn-on” signal for acute inflammation.

To recap here, a horse will have clinical signs and acute inflammation, elevated CRP and no measurable P2 antibody and it is treatable. As disease progresses a little more, we measure antibodies against whole myelin P2. Further along, with more progressive disease, the horse may become refractory to the whole P2 protein, those antibodies decline, and only the T-cell stimulating protein antibodies (neuritogenic peptide) linger, most horses are still treatable and need management. Once the body fibroses damaged nerves and myelin is no longer exposed, the the antimyelin P2 antibodies decline. Nerves can’t conduct signals yielding clinical signs that are progressively worse. And the horse is untreatable.



The nervous system is composed of a central and peripheral system. The peripheral nervous system is the part of the nervous system that consists of the nerves and bundles of nerve cells on the outside of the brain and spinal cord. A picture is worth a thousand words, look at the picture and let’s fast forward to myelin. Myelin is made of proteins, proteins are made up of amino acids. Groups of amino acids are called peptides, peptides can be as small as two amino acids.

Myelin insulates axons, the axon is a long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells. If myelin, made up of proteins, is damaged then messages are not transmitted to cells. Myelin proteins are highly similar, conserved, between species. And that is important to the study of polyneuritis equi (PNE).

When scientists (primarily the English and French) were investigating all manner of neurodegenerative diseases in people they got huge amounts of myelin from the spinal cords of cows because all animals have the same protein structure for myelin. This phenomenon is called conservation. Unfortunately, in 1984 an English cow developed strange signs that turned out to be the first recognition of Mad Cow disease.

Let’s digress, I like this part of history and what it gave us. The source of Mad Cow disease was animal feed. Specifically, animal feed contaminated with bits of protein called “prions”. First, disease was linked to sheep--but now some believe human bone might have gotten into the British animal feed. Doctors Alan and Nancy Colchester write that Indian and Pakistani peasants sometimes gather large bones from land and rivers to sell, and that "Hindus believe that it is essential for their remains after death to be disposed of in a river, preferably the Ganges. The ideal is for the body to be burned, but most people cannot afford enough wood for full cremation." During the 1960s and 1970s, the U.K. got a lot of raw material for fertilizers from Bangladesh, Pakistan, and India. Humans were known to have Creutzfeldt-Jakob disease, the infection passed to cows through ground-up bones in animal feed, and then the cows gave it back to people. Fearful of Mad Cow scientists turned to the horse as a source of tissue for their research. This vast body of knowledge gave us a leg up on polyneuritis equi.

There were some distinct differences in the equine protein and the bovine protein. It is molecularly heavier because it has 3 more amino acids. Ok big deal, I’m being thorough. But an unexpected result was horses have more, much more, basic myelin P2 protein (lets call it P2) in their central nervous system tissue. And P2 protein makes up 2-15% of the peripheral nervous system protein. The amount and distribution of P2 is a big deal because disease affecting this protein will be more apparent in horses. Myelin P2’s function is in lipid transport and storage in the cell responsible to myelinate nerves. The take home message here is that it was possible to test these myelin making cells (Schwann cells) for damage. If Schwann cells are damaged myelin production would decrease measurably.

Progressive neurological disease was induced in experimental animals by injecting myelin protein. This was important because a model using laboratory animals allowed controlled experiments. In the case of P2, an animal model for Guillian-Barre syndrome, a demyelinating disease of the human peripheral nervous system, was produced. If Schwann cells are damaged myelin production would decrease measurably in the model animals.

It wasn’t long before a connection was made to neuritis of the cauda equina, now called polyneuritis equi, a neurodegenerative disease in horses. Another similarity between Guillian-Barre and P2 neuritis was paralysis of the trigeminal and facial nerves. Cranial nerve involvement was also recognized in horses.

As an aside, this work was going on in 2005, some purified myelin protein became available. Horse neurologists got some purified spinal protein, injected it into a few horses, but didn’t get disease. Case closed. No more work on cauda equina induction by myelin protein. This small experiment closed the door to a model and produced a bias against this line of research that continues today. Did they use P2? And as you are going to see, different parts of myelin P2 can give different results in laboratory animals.

Back in Europe scientists purified equine myelin P2 and crystallized the protein giving them a highly refined molecule. There was another unexpected result of the P2 experiments that may relate to the small horse study. Myelin P2 was snipped (chemically) into peptides, different peptides and disease depended on the peptides that were used in the experiment. Some peptides did not cause disease whereas the whole purified protein did. The conclusion was that there must be a disease-inducing region of the protein. One peptide caused neuromuscular disease and weakness that would resolve, untreated. Another neuritogenic (disease causing) peptide consistently induced disease. Animals could become desensitized to disease-causing injections of the whole protein P2, but not to the neuritogenic peptide.

And, normal animals that were given blood cells (T-cells) from diseased animals (passive transfer) got disease! The disease was produced from immune cells from animals, not the protein itself. This raised several questions, but we’re going to cut to the chase. It wasn’t a malfunction of the cells that put myelin around axons. The myelinating cells did not change the proteins they made, nor did they change the capacity to remyelinate damaged axons in the face of disease.

What changed was the transfer of sensitized cells to a healthy animal. Researchers found that the sensitized cells induced the production of another protein, an immunoglobulin-binding protein on nerves that increased during the clinical deficit. The net result was now there was an increase in the ability of inflammatory cells to bind nerve cells. The nerve cells became the target of the body’s immune system.

What about that neuritogenic peptide? The neuritogenic peptide of P2, the myelin protein that wraps around axons, turned out to contain an inflammatory receptor that is recognized by the immune system. It participates in inflammatory reactions regulating cells that are involved in cell-to-cell signaling by molecules called cytokines.

In health, the neuritogenic peptide of P2 (and P2) are not exposed to the body’s immune system. When myelin is damaged and P2 is exposed disease ensues. Clinical signs manifest because the exposed peptides sensitize T-cells that stimulate a protein to bind immunoglobulin and make peripheral nerves a target of inflammation.