CD1 EXPRESSION DEFINES SUBSETS OF FOLLICULAR AND MARGINAL ZONE B-CELLS IN THE SPLEEN - BETA(2)-MICROGLOBULIN-DEPENDENT AND INDEPENDENT FORMS

We have used multicolor FAGS analysis, immunohistology, and functional assays to study the expression of CD1 on B cell subsets from normal a nd beta 2m(-/-) mice, Two B cell subpopulations were identified that e xpress high levels of CD1 in normal mice: splenic marginal zone B cell s (IgM(high) IgD(low) CD21(high) CD24(intermediate) CD23(-) CD43(-)) a nd a newly identified subpopulation of follicular B cells. The latter cells are unusual, because they are IgD(high) CD23(+), like follicular B cells, but express high levels of CD21 and IgM, an expression patte rn that is associated with marginal zone B cells. Therefore, the high- level expression of CD1 and CD21 was found to be closely associated on splenic B cells, Immunohistology confirmed the expression of CD1 on m arginal zone B cells and on clusters of B cells in splenic follicles, Both the high-level CD1 expression by these cells and the low-level CD 1 expression by subpopulations of B cells in the spleen, lymph node, p eritoneal cavity, and bone marrow were markedly reduced in beta(2)m(-/ -) mice. Despite this, a CD1-restricted T cell clone proliferated vigo rously in response to LPS-activated spleen cells that had been obtaine d from both beta(2)m(-/-) and wild-type mice. This response was inhibi ted by the 3C11 anti-CD1 mAb, These results show the heterogeneity of B cell subsets in their expression of the beta(2)m-dependent form of C D1. They further suggest that a beta(2)m-independent form of CD1 is ex pressed on B cells that can stimulate T cells; however, this form is n ot easily visualized with the anti-CD1 mAb used here.