Antigen presentation.

This paper reviews some of the cellular events involved in the immune recognition of foreign proteins. The recognition of an antigen by T lymphocytes is essential for its effective elimination by the host. T lymphocytes of the CD4 or CD8 subset recognize antigen but only after the antigen is handled by antigen-handling cells (antigen-presenting cells). Antigen molecules are recognized after an internal processing event by antigen-presenting cells that results in the generation of immunogenic peptides. Such peptides associate with histocompatibility molecules to form bimolecular complexes on the cell surface. The T cell receptors for antigen recognize the bimolecular complex and initiate the events that result in an inflammatory response. Antigen-presenting cells also produce molecules - termed costimulators - that stimulate the growth and differentiation of T lymphocytes.