RAT BONE-MARROW-DERIVED MAST-CELLS COCULTURED WITH 3T3 FIBROBLASTS INTHE ABSENCE OF T-CELL DERIVED CYTOKINES REQUIRE STEM-CELL FACTOR FOR THEIR SURVIVAL AND MAINTAIN THEIR MUCOSAL MAST CELL-LIKE PHENOTYPE

When cultured without fibroblasts, rat bone marrow-derived mast cells (BMMC) contain abundant rat mast cell proteinase type II (RMCP-II), an d exhibit survival and proliferation when maintained in mesenteric lym ph node conditioned medium (CM). When BMMC were co-cultured with 3T3 f ibroblasts in the absence of CM, BMMC numbers increased for 7 days and the BMMC survived for up to 23 days. There was a gradual loss of stor ed RMCP-II in BMMC that were cocultured with 3T3 cells, but the fibrob last microenvironment did not induce a detectable increase in the low levels of the connective tissue mast cell (CTMC)-associated proteinase , RMCP-I, in the BMMC. Nor did 3T3 cell co-culture induce significant heparin synthesis in BMMC as judged by the cells' reactivity with the fluorescent heparin-binding dye, berberine sulphate. These results sug gest that rat BMMC, unlike murine BMMC, do not have the potential to d evelop multiple CTMC-like characteristics upon co-culture with 3T3 cel ls. However, when BMMC and fibroblast co-cultures were treated with an antibody to recombinant rat stem cell factor (rrSCF), mast cell survi val was completely abrogated. This result suggests that endogenous, fi broblast-derived SCF is essential for the maintenance of rat BMMC viab ility in the absence of CM. On the other hand, prior treatment of the fibroblasts with the anti-rrSCF antibody did not affect the adherence of BMMC to the monolayer, implying that (an)other molecule(s) is(are) involved in the attachment process. The demonstration that rat BMMC su rvival on fibroblasts in vitro is dependent upon SCF may indicate an i mportant mechanism by which tissue mucosal cells can be maintained in vivo in the absence of T-cell derived factors.