ABSTRACT
Autoimmunity is an immune reactivity involving either antibody-mediated (humoral) or cell-mediated limbs of the immune response against the body’s own (self) constituents, i.e., autoantigens. It may induce autoimmune disease if there has been a breach in peripheral tolerance mechanisms. When autoantibodies or autoreactive T lymphocytes interact with self-epitopes, tissue injury may occur; for example, in rheumatic fever the autoimmune reactivity against heart muscle sacrolemmal membranes occurs as a result of cross-reactivity with antibodies against streptococcal antigens (molecular mimicry). Thus, the immune response can be a two-edged sword, producing both beneficial (protective) effects and leading to severe injury to host tissues. Reactions of this deleterious nature are referred to as hypersensitivity reactions and are subgrouped into four types.
