Inverse relationship of CA2+ mobilization and cell proliferation in CD8+ memory and virgin T cells

Memory T cells can now be defined with various monoclonal antibodies but little is known about the functional properties of these cells as compared to virgin T cells. We have studied Ca2+ mobilization and proliferation of memory and virgin cells in both the CD4 and CD8 subsets in response to phytohemagglutin-in. Using two-color fluorescence (yellow, red) for cell surface staining combined with two-color fluorescence for the Ca2+ chelator indo-1 (violet, blue) we can demonstrate that CD8+UCHL1+ memory cells exhibit a 1,5-fold higher influx than the CD8+UCHL1- virgin cells. The same pattern was obtained when CD8 memory and virgin cells were defined by a reciprocal marker (Leu-18) indicating that the higher response of memory CD8 cells is independent of the monoclonal antibody used to identify the cells. For the respective CD4 subsets no such clear-cut pattern of Ca2+ influx was evident. Analysis of proliferation in both subsets indicates that CD8+UCHL1- cells strongly proliferate in response to PHA, while CD8+UCHL1+ memory cells show only a minimal response with the average cpm values being 6-fold lower. In some instances no proliferation at all was detectable in the CD8+UCHL1+ cells. Identification of the subsets by reciprocal markers confirmed the lower proliferative response in the CD8 memory cells. Hence, within the CD8 compartment the memory cells, after phytohemagglutinin stimulation, exhibit a high Ca2+ mobilization but a low to absent proliferation, while the converse is true for the naive cells. These data show that (a) Ca2+ mobilization and proliferation are inversely correlated and (b) an initially vigorous response of memory cells may be subject to negative control mechanisms.