T cell-dependent B cell activation.
B cells obtain help from T cells in the antibody response by acting as antigen-specific antigen presenting cells. A direct signal through binding of antigen to membrane Ig can enhance B cell antigen presentation and T-dependent B cell activation, but is not required for a productive interaction between a small resting B cell and a differentiated helper T cell. As a result of helper T cell recognition of antigen on the B cell surface, the T cell becomes activated and in turn activates the B cell. T cell help has two components: lymphokines which act as growth and differentiation factors for B cells, and additional signals which require cell contact and enable B cells to respond to lymphokines. Contact help activity is regulated like lymphokine synthesis and secretion. Because contact help activity is retained by fixed, activated helper T cells and plasma membranes prepared from activated T cells, contact help is likely to be owing to new proteins expressed as membrane-bound lymphokines or activation antigens on helper T cells. Once induced, contact help can be delivered to B cells independently of recognition of antigen/class II MHC. A newly identified activation antigen of helper T cells, a ligand for the B cell differentiation antigen, CD40, is a key component of contact help. The roles of other T and B cell membrane molecules in contact help are reviewed.
Parker
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DC
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
D000818:Animals; D000917:Antibody Formation; D000938:Antigen-Presenting Cells / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D002448:Cell Adhesion / Q000276:immunology; D016207:Cytokines / Q000276:immunology; D006649:Histocompatibility Antigens; D006801:Humans; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D011947:Receptors, Antigen, B-Cell; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D016207:Cytokines; D006649:Histocompatibility Antigens; D011947:Receptors, Antigen, B-Cell