Relationship between macrophage infiltration and epidermopoiesis in delayed-type hypersensitivity.

The relationship between epidermopoiesis and macrophage infiltration was studied in delayed-type hypersensitivity (DTH) skin lesions in guinea pigs that had been sensitized with heat-killed tubercle bacilli or bovine serum albumin (BSA). Macrophages were identified with acid-phosphatase and nonspecific esterase stains, and the epidermal proliferative response was studied at DTH challenge sites by autoradiography. The number of macrophages in the sensitized animals was higher than that in the nonsensitized animals 48-72 h following challenge injections, when labelling indices were also elevated in the former group. Soluble factor(s) from cultured macrophages transiently enhanced the DNA synthesis of epidermal cells in cultures and in the sites injected with the factor(s). These results suggest that macrophages retained in the DTH lesion may play a role in an acceleration of epidermal proliferation, thus leading to acanthosis and lichenification.