Detection of in vitro macrophage colony-forming cells (M-CFC) in mouse bone marrow,spleen, and peripheral blood

In vitro macrophage colony-forming cells (M-CFC) have been detected in bone marrow (BM) (317/10⁵ cells), spleen (SPL) (81/10⁵), and peripheral blood leukocytes (PBL) (242/10⁵) of the mouse. These M-CFCs were similar to those previously detected in thymus (T) (30/10⁶) and lymph node (LN) (22/10⁶) tissue in several respects. BM- and SPL-derived M-CFC required PMUE to consistently initiate colony formation, whereas PBL-derived M-CFC formed colonies with stimulation by either PMUE or L-cell-conditioned medium. All colonies formed showed a singular macrophage line of differentiation, a lag of 13 to 18 days prior to initiating colony formation, a marked ability to survive in culture in the absence of PMUE, and markedly slow rates of appearance in culture once colony formation was initiated. The macrophage progeny were identified on the basis of morphology, glass adherence, the phagocytosis of agar, bacteria and SRBC, and the presence of receptors for IgG. These characteristics are also shared by those macrophage CFCs observed within stimulated peritoneal exudate, pleural effusion, and alveolar space. These M-CFCs are most likely members of a large, heterogeneous population of macrophage progenitor cells distributed throughout the hemato-lymphopoietic organs, serosal cavities and surfaces, and inflammatory and alveolar tissue sites. The degree of heterogeneity may be determined in part by the influence of tissue-specific microenvironment.