Reversible expression of CD138 on mature follicular B cells is downregulated by IL-4

CD138, known as a marker of plasma cells, was reported to be expressed to an intermediate level in the murine bone marrow precursor B cells. Here an intermediate level of CD138 expression was also noted in a subpopulation of splenic follicular B cells, which were distinguishable from CD138high plasma cells, whereas the majority of transitional or marginal zone B cells did not express CD138. These CD138int B cells were IgMlowIgDhigh mature B cells, located within follicular B cell zone, and expressed a lower level of CD21 than CD138− follicular B cells. During in vitro culture of splenic cells, the proportion of CD138int B cells increased, which was noticeably reversed by the addition of IL-4 to the culture. The experiments with sorted CD138int cells showed that IL-4-mediated regulation of the CD138 expression was B cell-intrinsic and independent of in vitro B cell death. Our results demonstrate that mouse CD138int B cells characterize a subpopulation of IgMlowIgDhigh mature follicular B cells. The CD138 expression on follicular B cells may represent a reversible status, reflecting a dynamic state probably influenced by IL-4.