IL-6 RESCUES RESTING MOUSE T-CELLS FROM APOPTOSIS

It has previously been demonstrated that mature mouse T cells live for many weeks in vivo. In contrast, explanted lymph node or splenic T ce lls undergo spontaneous death within days, suggesting that survival fa ctors supplied in vivo are not present in normal tissue culture medium , We discovered that IL-6 call rescue resting T cells from apoptosis i n vitro. We show that recombinant mouse IL-6 as well as IL-6 in endoth elial cell supernatants are sufficient to rescue T cells from death in the absence of additional cytokines, We show that CD4(+) T cells expr ess Bcl-2 immediately following isolation from the mouse, but after 24 h in culture Bcl-2 is undetectable, If during this time period the T cells are incubated with rIL-6, Bcl-2 expression is not downregulated, It is, therefore, possible that IL-6 rescue from death is mediated by maintenance or induction of Bcl-2 expression, Addition of rIL-6 does not by itself induce blastogenesis or proliferation, and therefore, th is cytokine appears to be a true survival factor rather than a mitogen ic factor for resting T cells. Together, these results support a poten tial role for IL-6 as one of the factors important for prolonging rest ing T cell survival in vivo.