VIRAL SUPERANTIGEN DRIVES EXTRAFOLLICULAR AND FOLLICULAR B-CELL DIFFERENTIATION LEADING TO VIRUS-SPECIFIC ANTIBODY-PRODUCTION

Mouse mammary tumor virus (MMTV[SW]) encodes a superantigen expressed by infected B cells. It evokes an antibody response specific for viral envelope protein, indicating selective activation of antigen-specific B cells. The response to MMTV(SW) in draining lymph nodes was compare d with the response to haptenated chicken gamma globulin (NP-CGG) usin g now cytometry and immunohistology. T cell priming occurs in both res ponses, with T cells proliferating in association with interdigitating dendritic cells in the T zone. T cell proliferation continues in the presence of B cells in the outer T zone, and B blasts then undergo exp onential growth and differentiation into plasma cells in the medullary cords. Germinal centers develop in both responses, but those induced by MMTV(SW) appear later and are smaller. Most T cells activated in th e T zone and germinal centers in the MMTV(SW) response are superantige n specific and these persist for weeks in lymph nodes draining the sit e MMTV(SW) injection; this contrasts with the selective loss of supera ntigen-specific T cells from other secondary lymphoid tissues. The res ults indicate that this viral superantigen, when expressed by professi onal antigen-presenting cells, drives extrafollicular and follicular B cell differentiation leading to virus-specific antibody production.