Expression of chemokine mRNA in HMC-1 cells. HMC-1 cells were cultured in the absence or presence of a mixture of rhSCF (100 ng/mL) and PMA (50 ng/mL) for various time periods as indicated. Thereafter, the cells were harvested and Northern blot analysis performed as described in the text. Unstimulated HMC-1 cells expressed MCP-1 mRNA, but no detectable amounts of mRNA specific for MIP-1α, MIP-1β, or IL-8. Stimulation of HMC-1 cells with rhSCF and PMA lead to a substantial increase in expression of MCP-1 and MIP-1β mRNA and minimal expression of MIP-1α mRNA, whereas transcripts for IL-8 were not detectable. Incubation of HMC-1 cells with rhSCF alone (without PMA) was also followed by an increase in MCP-1 mRNA expression, with a similar increase in mRNA when compared with cells exposed to rhSCF + PMA (not shown).