Mouse B-1 cell-derived mononuclear phagocyte, a novel cellular component of acute non-specific inflammatory exudate

At least three B cell subsets, B-1a, B-1b and B-2, or conventional B cells are present in the mouse periphery. Here we demonstrate that B-1 cells spon taneously proliferate in stationary cultures of normal adherent mouse perit oneal cells. B-1 cells were characterized by morphology, immunohistochemist ry and flow cytometry. IgM was detected in the supernatants of these cultur es. We demonstrated that the major cell population analyzed expresses the B -1b phenotype. When these cells were transferred to a new culture, a large proportion of them adhere to the plastic surface, and spread as bipolar cel ls endowed with the capacity to phagocytose via Fe and mannose receptors. F low cytometry analysis of these adherent cells demonstrated that the great majority of them share both B-220 and Mac-1 antigens. Nevertheless, 45% of them were exclusively Mac-1(+). Finally, when they were labeled in vitro wi th [H-3]thymidine and transferred to the peritoneal cavity of naive mice, t hey migrate to a non-specific inflammatory focus induced by a foreign-body implant. These data demonstrate that B-1 cells, mainly B-1b cells, not only proliferate and differentiate into a mononuclear phagocyte in vitro, but a lso that they exit the peritoneal cavity and migrate to a non-specific infl ammatory milieu.