Quiescent memory B cells in human peripheral blood co-express bcl-2 and bcl-xL anti-apoptotic proteins at high levels (original) (raw)
1998, European Journal of Immunology
The anti-apoptotic proteins bcl-2 and bcl-x L seem to exhibit strictly opposite expression patterns in normal lymphoid cell differentiation stages, with bcl-2 low and bxl-x L high in immature and mature proliferating cells, the reverse being the case in recirculating quiescent cells. However, it is in fact not known whether recirculating memory cells are bcl-x L low or high. We analyzed memory (immunoglobulin isotype-switched) B cells in human peripheral blood, which were small lymphocytes in the G0 phase of the cell cycle, but proliferated better than naive B cells in response to Staphylococcus aureus Cowan I. Ex vivo these cells coexpressed bcl-2 together with bcl-x L mRNA and protein at high levels. The mcl-1 mRNA level was low. The bcl-x L mRNA level decreased during culture in medium containing fetal calf serum, which implies that it is maintained in vivo by continuous or frequent, non-mitogenic signal(s). The high bcl-x L expression of memory B cells may be relevant with regard to their longevity and/or their capacity to undergo an accelerated secondary type immune response.
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