In vivo studies of factors influencing mast cell numbers in rat skin.

In order to examine the biological relevance of known in vitro stimuli for mast cell growth, the following substances were injected at two day intervals into the skin of Wistar rats: Ascaris Ag, epidermal growth factor, basic fibroblast growth factor, fibronectin, phytohemagglutinin-stimulated spleen cell supernatants, L-cell fibroblast supernatants and horse serum alone or in combination with L-cell supernatants. In some experiments, rats were also injected with fresh or cultured peritoneal cells. Single injections of the different factors had no significant effect on mast cell numbers. After multiple injections (4-10 x), deep dermal and submuscular mast cell numbers increased most markedly in ascaris sensitized animals at sites of ascaris antigen injections and in normal animals in response to a combination of horse serum and L-cell supernatants. Less pronounced increases occurred with all other test substances except for epidermal growth factor which was inactive. Mast cell numbers were also increased at sites of injections of immature, cultured mast cells and less so after injections of mast cell precursors and mature cells. Taken together, these data show that in vivo growth and differentiation of cutaneous mast cells can be influenced by several fibroblast- and lymphocyte-derived growth factors.