| Abstract
| - Antl-lg stimulated murine B cells express high levels of surface CD5 (ly-1) and increased CD44 while maintaining surface IgD, CD23 and J11d. Sorting of CD5− and CD5+ cells demonstrates that anti-lg induces CD5 expression rather than the selective expansion of CD5+ cells. Anti Ig plus interieukln-6 (IL-6) induces the CD23, IgD, low ly-5 (B220) (CD45low), J11dhigh phenotype of typical CD5+ peritoneal B cells. In contrast, lipopolysaccharide (LPS)-stimulated B cells have high levels of CD44 but decreased surface IgD, CD23 and J11d and no CD5. Thus LPS and anti-lg generate activated cells with differing phenotypes. Induced CD5+ cells have increased viability, even in the absence of added exogenous factors, while the viability of CD5− B cells is dependent on factors such as IL-4. We conclude that conventional CD5− B cellscan be activated by either of two pathways: one generating CD5+ B cells; the other yielding conventional activated cells. We hypothesize that the first path requires slg cross-linking and corresponds to T-independent (type 2) stimulation, while cognate Interaction with helper T cells in the absence of slg cross-linking induces B cells to enter the second path.
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