Collagen production by macrophages in tumour encapsulation and dormancy.

Dormant and regressing implants of C3H mammary carcinoma MC2 were always found to be surrounded by a cellular fibrous capsule where macrophages and T cells predominated as the cellular elements. Macrophages were always closely associated with the collagen deposition, and stained with anti-collagen type I immuno-peroxidase in tissue sections. The capacities of macrophages and T-lymphocytes to function in collagen formation was investigated with the use of Nucleopore chambers implanted i.p. in normal mice. The procollagen that entered the chambers via the pores, was assumed to have been produced by the packed layer of peritoneal macrophages that adhered firmly to the outside of washed chambers. The adherent cells all stained with Mac-1 immuno-peroxidase, and phagocytosed yeast in short-term culture. The formation of collagen fibres in the chambers was enhanced if the chambers contained T lymphocytes. It appears that macrophages have the capacity to function as collagen producing cells in tumour encapsulation.