Fibroblast‐dependent growth of mouse mast cells in vitro: Duplication of mast cell depletion in mutant mice of w/wv genotype

Abstract
In spite of the apparent depletion of mast cells in tissues of mutant mice of W/Wv genotype, cells with many features of mast cells do develop when bone marrow cells of W/Wv mice are cultured in the presence of pokeweed mitogen‐stimulated spleen cell‐conditioned medium (PWM‐SCM). In order to resolve this discrepancy and facilitate the analysis of the W mutation, we attempted to establish an in vitro system in which the in vivo defect of W/Wv mice can be reproduced. Cultured mast cells (CMC) were developed from bone marrow cells of either W/Wv or congenic +/+ mice, and then co‐cultured with NIH/3T3 mouse fibroblasts in media supplemented only with fetal calf serum (i.e., in the absence of PWM‐SCM). Under this condition, CMC from +/+ mice continued to divide and were maintained for more than 4 weeks. The supportive effect of NIH/3T3 cells required close‐range interactions with CMC and was not due to synthesis of the known mast cell growth factors, interleukins 3 and 4. By contrast, CMC from W/Wv mice were not maintained, and the number of mast cells remaining after 4 weeks of co‐culture was only 1% of the normal +/+ counterparts. Thus, the humoral factor‐independent and cell contact‐dependent system presented here revealed the intrinsic defects in growth and differentiation of CMC derived from W/Wv mice and might be useful for biochemical and molecular analysis of the gene product(s) encoded at the W locus.