CLASSIFICATION OF AUTOIMMUNE DISORDERS
Autoimmune disorders are often classified according
to whether they are organ-specific, affecting only one organ or are systemic
that is, affecting multiple organ systems (Table
5.7). In addition, destruction of cells and tissues can be brought about by
autoantibodies and/or cell-mediated immunity. For example, in multiple
sclerosis (MS) patients produce antibodies against myelin, the fatty material
surrounding the axons of nerves. In addition, MS patients have TH and TC lymphocytes in
their blood and cerebrospinal fluid, which are specific for myelin protein.
Thus, humoral and cell-mediated autoimmunity may contribute to the
demyelination of nerves in MS patients. In some instances, autoantibodies can
block or stimulate a cell receptor. Myasthenia gravis is an example of the
former, while Graves disease is an example of the latter. Like most
classification schemes, that of autoimmune disorders is not perfect. For
example, Goodpasture’s syndrome directly affects both kidneys and lungs while
MS exerts systemic effects by attacking one type of tissue only.
Many, but not all, autoimmune disorders, affect a
preponderance of female patients, with three times as many females as males
presenting with autoimmune diseases. The reasons for this gender bias are
unclear but may be related to sex hormone levels. Many autoimmune disorders
show a link with the type of MHC antigens that are present on cells. In humans,
the MHC is known as the HLA system. The links between HLA type and different
diseases is described. So, for example, patients with Goodpasture’s syndrome
have a higher incidence of HLA-DR2 than the healthy population.
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