Augmented in vitro presentation of Mls determinants after anti-immunoglobulin-induced B cell activation: ontogeny and role of purified B cells.

Murine splenocytes which contained B cells activated by in vivo exposure to affinity-purified goat anti-mouse IgD (GaMD) antibody were utilized to present major histocompatibility complex (MHC) and non-MHC minor lymphocyte-stimulating (Mlsa) determinants in a primary mixed lymphocyte reaction (MLR). As the time in hours after in vivo exposure to GaMD increased, splenocytes from adult mice showed a co-ordinate increase in cell size, expression of public and private MHC class II antigenic determinants and MHC and Mlsa antigen-presenting capacity. This augmented alloantigen-presenting capacity was demonstrable with either irradiated or mitomycin C-treated adult splenocytes. In contrast, GaMD-treated neonatal splenocytes from 10-day-old mice demonstrated no significantly increased class II expression or enhanced MHC stimulatory capacity, but nevertheless triggered augmented responder cell proliferation across an Mlsa barrier. Thus, increased class II expression or presenting capacity may not be required for an augmentation in splenocyte Mls-stimulating ability to occur. In vitro exposure of T cell-depleted splenocytes or highly purified small resting B cells to GaMD or lipopolysaccharide (LPS) induced a substantially increased ability in those populations to present MHC and Mlsa antigens in a primary MLR. Hence in vivo or in vitro activation of B lymphocytes in a stimulator cell population may yield more effective presentation of MHC and non-MHC determinants.