Suppressor activity of bone marrow cells and localization of fluorescent-labeled bone marrow cells within ovine...

Numbers of fluorescein isothiocyanate (FITC)-labeled bone marrow (BM) cells of donor lambs were quantified within endometrial cell suspensions following their administration to ovariectomized (OVX; control-and estradiol-17beta-treated) and intact (estrus, d-14 cyclic and pregnant) ewes. The numbers of fluorescent BM cells were greater (P < .05) for the estrous and d-14 cyclic ewes than for both groups of OVX ewes. Fractionation of the endometrial cells with Percoll revealed that the majority of fluorescent cells were low-density (1.002 to 1.056 g/mL) cells. In coculture experiments, low-density cells from lamb BM not only suppressed the incorporation of thymidine into phytohemagglutinin-treated peripheral blood lymphocytes, but the cells also released suppressor factor into the culture medium. Suppressor activity tended to be reversed (P < .1) by a pan-specific neutralization antibody to transforming growth factor-beta (TGF-beta); however, the activity was unaffected by a neutralization antibody to TGF-beta2. These findings suggest that ovine endometrial suppressor cells may represent a population of low-density BM-derived natural suppressor cells, and their trafficking and localization patterns may depend on an ovarian factor(s). Further, suppressor activity does not seem to be mediated by TGF-beta2.