Contemporary concepts of autoimmunity and autoimmune diseases.

No single theory or mechanism can explain the phenomenon of autoimmunity and autoimmune diseases. Not all autoimmune responses are harmful or "forbidden." Considerable research has indicated that autoimmune response may be normal and important in the regulation of the immune system. Autoimmunity may play a role in a wide range of clinical states including physiological clearance of dead cells, and cell components, aging, response to viral and microbial infections, and generalized immunological diseases. There are many factors involved in autoimmunity including genetic, hormonal, immunological, and environmental factors. The susceptibility to autoimmune diseases is multifactorial and polygenic. There is a definite association of the autoimmune diseases with MHC alleles. Also, non-MHC genes are involved in disease susceptibility. Numerous mechanisms of autoimmunity have been discussed. There may be an alteration with dysregulation of the immune system with defective generation of normal suppressor mechanisms or an altered neuroendocrine regulation. The altered immune system will make the host more susceptible to autoimmune disease. Autoimmune reactions can occur in a host with a normal immune system. Some examples are as follows: 1. Infection or damage to host target organ with release or alteration of autoantigen 2. Molecular mimicry or cross-reactivity between virus or bacteria and host autoantigens 3. Abnormal expression of MHC molecules by antigen-presenting cells in target cells resulting in activation of autoreactive T-cells. 4. Drug administration