Accumulation of CD138+ T cells in an SLE murine model
Syndecan-1 (sdc-1, CD138) is a heparan sulfate proteoglycan that modulates multiple biological and immune activities, such as cellular multiplication and differentiation 15. CD138, which is also expressed in epithelial cells and other adherent cells, has been thought to be a marker for plasmablasts and plasma cells in lymphocytes, which have been suggested to have originated from activated B cells16, 17. CD138 has also been found on the surfaces of CD3 expressed T cells. CD138+ T cells have also been reported to be plasmablastic B-cell neoplasms in clinical cases 18. However, these abnormal CD138+ cells, i.e., CD138+ T cells, have also been identified in lupus mice; they were found to accumulate in spleens, lymph nodes, gut, and peripheral tissues in lupus mice as their ages increased 12-14.
CD138+ T cells mainly derive from DN T cells; a proportion of them derives from CD4+ T cells 13, 14. The frequency at which CD138+ T cells are derived from CD8+ T cells is negligible14. CD138+ T cells have been shown to constitute a small fraction of cells in the spleen of non-lupus prone mice, but not to significantly accumulate in MRL/lpr mice 14. This indicates that Fas-deficiency results in the accumulation of CD138+ T cells. Compared with CD138- T cells, CD138+ T cells have a lower level of proliferation 14. Importantly, the apoptotic number of CD138+ T cells has been shown to decrease dramatically, compared with CD138- T cells (unpublished data by Tianhong Xie et al.). Significantly increased levels of live cells and decreased apoptosis levels in CD138+ T cells induce the accumulation of CD138+ T cells in lupus mice, but hyper proliferation does not 14.