Overexpression of Id genes in BMMs does not affect phagocytosis. (A) BMMs were transduced with pMX-IRES-EGFP (control), Id1, Id2, or Id3 retrovirus and cultured for 2 days with M-CSF alone or M-CSF and TRANCE. Cultured cells were incubated with fluorescein-conjugated zymosan particles for 1 hour and washed with PBS. Cells were fixed and observed with UV illumination under a microscope. Fluorescein-conjugated zymosan particles incorporated by the cells appear as bright dots in the dark field (original magnification, ×100). (B) BMMs were transduced with control (pMX-IRES-EGFP) or Id2 retrovirus and cultured for the indicated days with M-CSF and TRANCE. RT-PCR was performed for the expression of TRAP, c-fms, CD14, F4/80, and HPRT. Images were acquired as described for Figure 2.