J11d is an antigen expressed on a variety of hemopoietic cells including B cells. In this report we describe the expression of J11d on functional subpopulations of B cells from adult mice of different ages or at different stages of an immune response. In addition we explore the relationship between the expression of J11d and that of other markers characteristic of memory B cells. Our results show that expression of J11d on B cells is related to the immunologic history of the host. Thus, J11d on B cells from normal mice is decreased as the mice age and are thereby exposed to environmental antigens. Down-regulation of J11d on B cells does not occur in germfree or nude mice but does occur when nude mice are reconstituted with T cells and/or are immunized. Since B cells expressing low levels of J11d accumulate following exposure to antigens, we also determined whether memory cells reside in the J11dlo cell population. To this end, we studied primed mice and found that expression of J11d on antigen-specific B cells increased during the first week after immunization and decreased thereafter. Increases in expression of J11d after activation also occurred in B cells stimulated with lipopolysaccharide (LPS) in vitro. However, antigen-specific B cells from long-term primed mice which expressed lower levels of J11d and antigen-specific receptors of higher affinity also expressed lower densities of sIgM and included most sIgG+ cells. Furthermore, these antigen-specific J11dlo B cells transferred a memory response, whereas J11dhi cells did not. Taken together, these data indicate that the level of expression of J11d on B cells distinguishes virgin (J11dhi) from memory (J11dlo) cells in mice.
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