EFFECTS OF INTERLEUKIN-3 WITH OR WITHOUT THE C-KIT LIGAND, STEM-CELL FACTOR, ON THE SURVIVAL AND CYTOPLASMIC GRANULE FORMATION OF MOUSE BASOPHILS AND MAST-CELLS IN-VITRO

We assessed the ultrastructure and the cell-surface expression of rece ptors for immunoglobulin E (Fc epsilon R), and c-kit, the receptor for stem cell factor (SCF), in mouse basophils and mast cells present in short-term cultures of mouse bone marrow cells in interleukin-3 (IL-3) with or without SCF. Basophils did not develop increased numbers of c ytoplasmic granules and underwent apoptosis in cultures containing IL- 3 and SCF, whereas mast cells thrived and developed increased numbers of granules. Basophils were nearly all Fc epsilon R(+) c-kit(-) when s orted after culture in IL-3 and SCF; most mast cells were Fc epsilon R (+) c-kit(+). However, a second population of Fc epsilon R(+) c-kit(-) mast cells was present after culture in IL-3 and SCF. These c-kit rec eptor-negative mast cells were less mature than c-kit(+) mast cells an d contained significantly fewer cytoplasmic granules than the c-kit(+) mast cells present in the same cultures (P<0.0010). Thus, mouse basop hils express little or no c-kit receptor on their surface, nor can the survive for long periods in SCF-supplemented cultures. By contrast, m ouse mast cells seem to express the Fc epsilon R early in their develo pment, even before they express detectable c-kit receptors on their su rface. IL-3 promotes cytoplasmic granule formation in immature mast ce lls, but even more granules are formed when c-kit receptor-positive im mature mast cells are cultured in both SCF and IL-3.