Enhancement of fibroblast-dependent mast cell growth in mice by a conditioned medium of keratinocyte-derived squamous cell carcinoma cells.

We investigated the increase in mast cell numbers at the sites of inoculation of keratinocyte-derived squamous cell carcinoma cell line (KCMH-1) cells in mice. A significant increase in the number of mast cells was observed at the sites of tumours developed at the sites of inoculation of the KCMH-1 cells. Enhancement of mast cell growth was observed by culturing bone marrow-derived mast cells (BMMC) on NIH/3T3 fibroblast monolayers in the presence of conditioned medium (TCM) obtained from KCMH-1. Activities of known factors for mast cell growth, such as interleukin-3 (IL-3), IL-4, IL-9, IL-10 and stem cell factor (SCF), were not detected in the TCM. Nerve growth factor (NGF) did not induce mast cell growth. Mast cell growth induced by the TCM needed 3T3 fibroblasts. These results suggest that KCMH-1 cells may produce a factor which induces mast cell growth with 3T3 fibroblasts, other than the already known mast cell growth factors. This may be the mechanism of mast cell accumulation at sites of tumours.