IL-3-mediated enhancement of particulate antigen presentation by macrophages

Mice were exposed to interleukin- (IL-) 3 in vivo by injection of tumor cells transfected with the IL-3 gene. At 10 days post tumor injection, bone marrow cells were recovered, pulsed with particulate antigen in the form of ovalbumin (Ova)-coated magnetic beads, and tested for their ability to present antigen via class I to an Ova/class I-restricted T cell hybridoma. Cells from IL-3-stimulated mice exhibited a marked increase in antigen presentation compared with cells from mice injected with control non-cytokine-secreting tumor cells. These cells were markedly more efficient at presenting particulate Ova antigen than in presenting soluble Ova. Based on adherence, radiation resistance, and surface markers, the cells presenting antigen appear to be in the macrophage cell lineage. These cells are susceptible to lysis by antigen-specific cytotoxic T lymphocytes, which may contribute to limiting the effectiveness of antitumor responses.