XXXX effects on human B cells activated in vivo.

@entity1199 @entity5041 @entity2902
While activated B cells, as well as T cells, can express functional @entity2902 ( @entity2902 ), the physiologic role of @entity1199 in B-cell responses is still in doubt. Accordingly, we have examined the role of recombinant @entity1199 ( @entity5041 ) in the proliferative response, @entity2902 expression, and the terminal differentiation of tonsillar B cells in comparative studies with T cells from the same source. For these analyses of physiologically activated lymphocytes, the B and T cells were first separated, then divided into subpopulations enriched for either resting or preactivated cells on the basis of relative cell density or activation antigen expression. As expected, the relatively low-density fraction of T cells was enriched for @entity2902 -positive (Tac+) cells and displayed vigorous proliferative responses to @entity1199 along with heightened @entity2902 expression. Moreover, limiting dilution analysis revealed that growth of these activated T cells could be perpetuated with the addition of @entity1199 . By comparison, relatively few tonsillar B cells expressed the @entity2902 . The addition of @entity5041 to cultured B cells of relatively low density resulted in an increase in Tac+ cells but only a minimal proliferative response. The subpopulation of tonsillar B cells expressing the Bac-1 activation antigen contained most of the @entity1199 inducible Tac+ B cells, and @entity5041 induced an efficient but transient proliferative response by these activated B cells. The @entity5041 -induced Tac+ B cells were noted to be relatively large. A fraction of these Tac+ cells, but not the Tac- cells, produced and secreted immunoglobulins. Incubation with @entity5041 enhanced the Ig secretion, and the anti-Tac antibody blocked this enhancement. Time-course analysis revealed that @entity5041 induced transient Tac expression, whereas mature plasma cells in 6-day cultures no longer expressed detectable @entity2902 . In conclusion, these observations suggest that @entity1199 transiently upregulates expression of @entity2902 , via which it induces the terminal growth and differentiation of activated B cells into plasma cells.
