Canine blood mononuclear cells mediate contact-dependent impairment of granulocyte-macrophage colony formation by bone marrow cells.

Nonphagocytic, nonadherent mononuclear cells from canine peripheral blood (PBMC) were shown to suppress colony formation in agar of autologous and allogeneic bone marrow granulocyte-macrophage progenitor cells (CFU-GM). Suppression required previous cell-to-cell contact in liquid culture between PBMC and bone marrow cells (BMC) and was time- and dose-dependent and resistant to x-irradiation with 20 Gy. Small BMC were less susceptible than large BMC, whereas day-7 and day-14 CFU-GM were equally suppressed. Cryo-preservation of BMC did not enhance CFU-GM inhibition. Spontaneous inactivation during liquid culture of CFU-GM or accessory cells by PBMC is the likely effector mechanism. Possible recognition structures are different from dog leukocyte antigens A and B. Canine PBMC or subpopulations thereof might participate in the regulation of normal hemopoiesis and in the rejection of hemopoietic stem cell grafts by natural killer cell-like mechanisms as has been suggested for human and murine natural killer cells.