Aim
Because MIF is historically thought to initiate signaling via a receptor-dependent, outside-in mode of action, we wished to investigate the specific contributions of tumor-derived vs. macrophage-derived MIF to M2 marker expression during macrophage polarization. Design: Murine oral squamous cell-carcinoma cells (SCCVII) were co-cultured with either the RAW 264.7 mouse macrophage cell line or mouse primary bone marrow-derived macrophages in the context of MIF genetic loss/inhibition individually or in combination each cell type.
Background
Tumor-associated macrophages (TAMs) are important determinants of intratumoral immune evasion, neoangiogenesis, extracellular matrix remodeling and dysregulated tumor cell proliferation. Our prior studies revealed that macrophage-derived, but not tumor cell-derived, macrophage migration inhibitory factor (MIF), is an important determinant of TAM alternative activation and M2 polarization.
Conclusion
These studies identify an important and dominant requirement for macrophage MIF in maximal Th2-cytokine and oral squamous carcinoma cell-induced macrophage polarization and M2 marker expression.
Methods
Twelve well Transwell plates were used to co-culture SCCVII cells and RAW 264.7, MIF+/+ or MIF-/- macrophages treated with/without the small molecule MIF inhibitor, 4-iodo-6-phenylpyrimidine and incubated in the presence or absence of interleukin (IL-4) for 48 h. Macrophages were analyzed by quantitative real-time polymerase chain reaction and/or immunoblotting for relative macrophage polarization marker expression.
Results
IL-4 treatment synergizes with SCCVII co-culture in inducing the expression of macrophage M2 markers and loss or inhibition of macrophage-derived MIF significantly reduces both IL-4 alone and IL-4/SCCVII co-culture-induced macrophage M2 marker expression.