The functional specificity of three types of macrophage chemotactic factors (MCFs), -a, -b, and -c, from purified protein derivative of tuberculin (PPD)-induced delayed hypersensitivity reaction (DHR) skin sites on guinea pigs, was analyzed using macrophage cell line cells, M1, established from myeloid leukemia cells of a SL/Am strain mouse. M1 cells yielded two subclones: Mk1 cells, which were Ia+ and migrated specifically toward MCF-c; and Mm1 cells, which were Ia- and migrated specifically toward MCF-a and -b. These differences show the heterogeneity of the biologic activities of the MCFs in the presence of cell line cells. M-1 cells, blast cells, when grown in continuous culture, migrated toward none of the MCFs. Upon differentiation to mature macrophage-like cells in conditioned medium (M+1 cells), however, they migrated to MCF-a, -b, and -c and the experimental evidence points to the possibility that M+1 cells are separated into subpopulations on the basis of their chemotactic response. Cytotoxic treatment of M+1 cells with anti-Ia antisera resulted in the specific decrease of activity toward MCF-c. Furthermore, MCF-c attracted Ia-positive M+1 cells, while MCF-a and -b attracted Ia-negative M+1 cells. Thus, our results indicate the existence of two migrating subpopulations of M+1 cells with specificities for MCF-a, and -b and for MCF-c, respectively. The data suggest that MCF-c attracts Ia-bearing accessory macrophages and MCF-a and -b attract Ia-negative macrophages in the DHR.
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