Figure 4. Tumor cell-secreted factors upregulate CD79a on myeloid cells and induce their expansion and migration.

(A) The ability of tumor cells of varying metastatic potential to induce expression of CD79a on immature myeloid cells from bone marrow of naïve mice was assessed using a Transwell® system (0.4 µm pore size) that prevented contact between tumor and bone marrow-derived cells. BM cells were co-incubated with tumor cells of medium alone for 48 h and then BM cells were analyzed by flow cytometry. (B) Representative FACS plots and histograms showing the effect of 4T1 secreted factors on the expansion of BM myeloid cells expressing CD79a, tested using a Transwell® system as in A. (C) Migration of BM cells in response to 4T1 secreted factors was tested in a Transwell® system as above, but using a 3.0 µm pore-size membrane to allow migration of BM cells towards the 4T1 cells in the well below. Cells that migrated through the membrane into the well below were collected, counted and analyzed by FACS for CD79a expression. Results are mean +/- SEM; n = 4 determinations.