IL-3 DERIVED FROM CD4(-CELLS IS ESSENTIAL FOR THE IN-VITRO EXPANSION OF MAST-CELLS FROM THE NORMAL ADULT-MOUSE SPLEEN() T)

A null cell line (SGM1) was established by a culture of spleen cells ( SC) from normal adult C57B1/6 mice with complete medium alone for 10 d ays and followed by weekly cultures with a 25% WEHI-3 cell culture sup ernatant. Phenotype analysis showed that the SCM1 cells were negative for CD3, Thy 1.2. B220, Mac-1, Gr-1, NK1.1 and MHC class II, but were positive for MHC class I, Fc gamma RII/III, Fc epsilon RI, c-kit and t he receptor against wheat germ agglutinin. These findings suggested th at the SCM1 cells were mast cells. In an in vitro proliferation assay, SCM1 cells proliferated in the presence of either IL-3 or stem cell f actor (SCF), bur not in the presence of IL-4, whereas IL-4 showed an a ugmenting effect on their proliferation in the presence of either IL-3 or SCF. In analysing the mechanism by which such mast cells could be expanded from normal adult mouse SC, the addition of anti-IL-3 MoAb, b ut not anti-SCF MoAb, into the initial culture inhibited the subsequen t expansion of either IL-3- or SCF-responding cells. The prior depleti on of CD4(+) T cells abrogated the capacity of the SC to enhance the e xpansion of SCF-responding cells, and this inability was restored by t he addition of IL-3. Moreover, the culture supernatant of normal adult SC alone contained considerable levels of IL-3. Taken together, our f indings suggest that, in an in vitro culture. CD4(+) T cell-derived IL -3 therefore enhances the expansion of mast cells from the normal adul t mouse spleen.