Stimulation of bone marrow-derived macrophages with lactate was sufficient to induce the expression of the M2-related genes Vegf, Arg1, Relma, Mgl1, and Mgl2. Interestingly, stabilization of HIF-1α by tumor-derived lactate was the actual driving force for this M2 polarization. The gene discussed is ARG1; the disease is neoplasm.