Origins of macrophage diversity: functional and phenotypic analysis of cloned populations of mouse splenic macrophages

Soft-agar colonies of mouse splenic macrophages were examined for surface and functional characteristics that might prove useful in studying the origin(s) of macrophage diversity. Flow cytoflurometric analysis revealed that essentially all cells in all of the colonies bore the Mac-1 and Mac-3 antigens. The colonies did not differ appreciably in their phagocytic activity or in their secretion of lysozyme, but did show different patterns of Mac-2 antigen expression. In most colonies, the cells expressed low levels of the antigen, and in the remainder they expressed a high or an intermediate level of Mac-2. The colonies also differed in their ability to present keyhole limpet hemocyanin (KLH) to an antigen-specific H-2-restricted T-cell hybridoma. About 6% of the colonies gave rise to subcultures with antigen-presenting activity. This presentation was always associated with subcultures containing a high proportion of Ia-bearing macrophages, but not all cultures with similarly high proportions of Ia-bearing cells presented KLH to the hybridoma. Indeed, the induction of Ia on all cells in all cultures increased the proportion of KLH-presenting subcultures only about twofold. The results show that not all splenic macrophages have the ability to process KLH and present it to a T-cell hybridoma. This suggests the presence of functionally specialized subpopulations of macrophages, possibly derived from distinct progenitors, in the spleens of mice.