ABSTRACT
The immune system provides protection against infection by microorganisms. The first line of defense against infectious pathogens is the innate immune response by neutrophils, NK cells, and macrophages, which differentiates between foreign organisms (nonself) and self-tissue, by recognizing “pattern recognition markers” using a limited number of receptors from germ line genes, resulting in the nonspecific elimination of invading microorganisms. Unlike innate immunity, the adaptive immune system of T and B cells are able to rearrange a limited number of germ line VJD (variable, joining and diversity) genes to produce a highly diversified repertoire of somatically mutated T cell (immunoglobulin-like) receptors and B cell immunoglobulin receptors. Following the phagocytosis of microorganisms during the innate immune response, specific peptides from the infectious pathogen are processed and presented to antigen-specific T cells by antigen-presenting cells (APC), thus activating the adaptive immune system (T and B cells). This results in the neutralization of the infectious pathogen, death of infected host cells, and the induction of antigen-specific memory T cells. In rare instances, T cells that recognize self-peptides may become activated, and induce autoimmune disease.
