The Role of Surface Immunoglobulin in the Processing and Presentation of Antigen
Helper T-cell responses to the globular protein antigens studied to date, require the uptake and intracellular processing of the protein by an Ia expressing antigen presenting cell (APC). Processing yields a peptide fragment, containing the T-cell’s antigenic determinant, which is displayed on the APC surface, where it is recognized by the helper T-cell in conjunction with Ia. Most cells which express Ia are competent APC, including macrophages, dendritic cells and B cells (Unanue, 1984). Since, with the exception of B cells, APC do not express immune receptors for antigen, processing can presumably be initiated by a nonspecific, fluid phase pinocytosis of the antigen. However, recent studies have indicated that B cells which bind antigen, or anti-Ig acting as a surrogate antigen, are far more effective APC, capable of maximally activating T-cells requiring many fold less antigen and fewer cells as compared to nonspecific B cells. The evidence suggests that the B-cell surface immunoglobulin serves to concentrate antigen for subsequent processing and/or to signal the cell to increase the level of activities required for its processing and presentation functions. However, the molecular mechanisms by which surface Ig serves to augment presentation remains largely unknown. The results of experiments described here indicate that the surface Ig is not uniquely suited to facilitate antigen processing or presentation, and that antigen artificially bound to other B-cell surface proteins, namely Class I and Class II, is also efficiently presented. In these cases, enhanced antigen presentation appears to be solely a function of the ability of the B cell surface structures to concentrate antigen for processing.
KeywordsAntigen Present Cell Antigenic Determinant Antibody Conjugate Cell Surface Structure Enhance Antigen Presentation
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