What is Autoimmunity:
Autoimmune disease occurs when the immune system initiates a specific response to a self protein . Autoimmune diseases result from a dysfunction of the immune system in which the body attacks its own organs,tissues, and cells. Physicians and scientists have identified more than 80 clinically distinct autoimmune diseases. Several are well known, including rheumatoid arthritis, multiple sclerosis, type 1 diabetes, and systemic lupuserythematosus; others are less familiar, including autoimmune hepatitis, Sjögren’s syndrome, autoimmune ear disease, and pemphigus. Collectively, these diseases afflict millions of Americans, an estimated 5 to 8 percent of the population – 14 to 22 million persons. The social and financial burdens imposed by these chronic, debilitating diseases include poor quality of life, high health care costs, and substantial loss of productivity.
CIDP is an autoimmune disease, which affects the motor and sensory nerves by destroying the myelin sheaths surrounding the nerves. The myelin sheath is a fatty covering acting as an insulator to the fibers of nerves . Without this covering, nerves incur greater damage with regular activity. There is strong evidence that the inflammation in the neural tissue is what causes the damage to the sheath and ultimately the nerves (Guillain-Barre Syndrome Support Group). This inflammation is macrophage mediated (Washington University). CIDP is thought to be the chronic variety of Guillain-Barre Syndrome (GBS), which is an acute immune mediated polyneuropath. There are two types of CIDP: chronic progressive, and relapsing. In chronic progressive patients, the disease gradually worsens over time. Relapsing patients show and ebb and flow of symptoms slipping in and out of remission over the course of their disease. The classification of CIDP does not typically change the course of treatment, but has some effect on the success of the treatment modalities (Washington University, 2003).
This disease is characterized by progressive weakness and loss of neurological function primarily in the legs and arms . Most patients with this disorder present with a case of progressive weakness for at least two months , the temporal indicator of the chronic form of this neuropathy. The course of the disease tends to be either slow and gradual, or characterized by periods of relapses and remissions Although this disease is slightly more prevalent in young adults, it can occur at any age, and statistics show that men are twice as likely as women to contract this disease . Some typical symptoms include: symmetric tingling in the proximal and distal extremities, paralysis of the muscles, progressive weakness, sensory loss, loss of nero-muscular reflexes, and frequent loss of balance. It is not uncommon for a CIDP patient to to lose the ability to feel the sharp sensation of a pin stick in the affected area.This onset is prolonged and gradual over the course of at least 8 weeks (Koski, 2002). Statistics show that 70% of patients diagnosed with CIDP presenting only sensory symptoms develop motor symptoms over the course of 2-3 years.
The main reason CIDP is considered an immune disorder
is that it responds to immune-mediated treatment . It is very
difficult to diagnose and can be diagnosed through a number of
methods which are discussed below. Although the aetiology remains
unknown, both humoral and cell-mediated immune mechanisms contribute
to the pathogenesis .Immune or inflammatory mechanisms are thought
to be the root cause of many disorders that, like CIDP, reflect
damage to the peripheral nerves and affect sensory function. This
turns out to be the most definite role of the immune system in the
development of CIDP; the mutation of the macrophage to cause
macrophage-mediated inflammation, ultimately resulting in the
demyelination of the nerves.
Another characteristic of CIDP, which leads to its classification as an autoimmune disorder, is the evidence of preexisting infections immediately prior to the development of the disease in a significant number of patients. Studies show that in 70% of GBS patients (Guillain-Barre Syndrome), the acute form of CIDP, have pre-existing infections prior to the development of symptoms. Although the pathology of the infections preceding CIDP are studied less frequently, statistics show that at the very least relapses are strongly correlated with infection.
The specific pathway for induction of the autoimmunity associated with CIDP is unknown. The current research cannot eliminate the possibility of an antibody mediated self-reactivity or a T-cell mediated self reactivity . The possibility that infection is a possible stimulus to the development of CIDP can support either pathway . Infections are capable of inducing co-stimulatory activity on antigen presenting cells that present low levels of the specific peptide being attacked, in this case myelin. Another pathway is that of molecular mimicry. In this situation, antibodies or T-cells generated in response to an infectious agent cross-react with self antigens (Janeway, 2001). A molecular mimic is a foreign antigen closely related in structure to a self peptide allowing an antibody mediated response mounted toward the mimicked peptide to also effect the self-protein.
What components of the immune system are involved?
The most widely explained mechanism for the demyelination of nerve cells in CIDP is a macrophage-mediated inflammatory response.Endoneurial inflammatory changes with T cell infiltrates and macrophage associated demyelination are present on nerve biopsies in patients in the acute phase of CIDP. These endoneurial lymphocytes are associated with the increase expression of mRNA for Tumor Necrosis Factor alpha (TNF alpha), Interferon gamma (INF gamma) and Interluekin-2 (IL-2). TNF alpha is involved in local inflammation and endothelial activation. INF gamma causes macrophage activation, increased expression of MHC molecules and Ig class switching. INF gamma also suppresses the less damaging TH2 response in favor of the inflammation mediation of TH1. IL-2 is a crucial chemokines for the adaptive immune response and aids in the proliferation of T-cells. All of these proteins are either produced by T-cells, Natural Killer Cells or Macrophages, or add to the existence of T-cells and cause the initial inflammatory response associated with infection . Activated T lymphocytes are increased in the peripheral blood of CIDP patients. This diagnostic evidence coupled with the relative success of T-cell suppressive treatment makes the case for a possible malfunction in the TH1 inflammatory response.
Antibodies and Complement:
These components of the immune system play a role in the pathogenesis of CIDP in the presence of a blood-nerve barrier breakdown. (after the demyelination has begun)
The current research debates whether CIDP is associated with a specific antibody response against neural antigens. Antibodies against selected neuroblastoma cells have been found in 40% of patients with CIDP and GBS in comparison with only 4% in other neuropathies . This, however, is far from conclusive as to the direct pathology of the disease, as other groups show no antibody interaction with myelin proteins or glycolipid cell-surface receptors.
Some forms of CIDP can be diagnosed using autoantibody serums to tubulin. Tubulin is a molecule which mediates many cell processes specifically cell division and movement of materials within cells. The suggested mechanism for the autoantibody to tubulin involves both IgG and IgM antibodies capable of binding to the tubulin epitope. This pathology was present in 10% of patients with CIDP (Washington University, 2003).
Another specific immunologic interference occurring in 26% of patients with CIDP is an interaction between IgG antibodies and Schwann cell processes. Schwann cells are the cells that wrap themselves around nerves making a protective barrier for the nerve fibers. Schwann cells are the individual cells making up the myelin protective sheaths. This suggests that a patient presenting with symptoms of CIDP could possibly have an autoantibody response against cell schwann cells. This response tags the self-protein for natural killer cell destruction.
( webresources) www.cidpusa.org