Quiescent memory B cells in human peripheral blood co-express bcl-2 and bcl-x(L) anti-apoptotic proteins at high levels.
The anti-apoptotic proteins bcl-2 and bcl-xL seem to exhibit strictly opposite expression patterns in normal lymphoid cell differentiation stages, with bcl-2 low and bxl-xL 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-xL 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 co-expressed bcl-2 together with bcl-xL mRNA and protein at high levels. The mcl-1 mRNA level was low. The bcl-xL 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-xL 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.
Bovia
F
F
Department of Medicine, Geneva University Hospital, Switzerland.
Nabili-Tehrani
A C
AC
Werner-Favre
C
C
Barnet
M
M
Kindler
V
V
Zubler
R H
RH
D017209:Apoptosis / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D015870:Gene Expression / Q000276:immunology; D006801:Humans; D007156:Immunologic Memory; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051020:bcl-X Protein