Degradation of collagen and proteoglycan by macrophages and fibroblasts. Individual potentialities of each cell type and cooperative effects through the activation of fibroblasts by macrophages.

Fibroblasts and macrophages of various sources (peritoneal, alveolar or bone marrow-derived), from either rabbit or mouse, were cultured, independently or together, at the surface of [3H]proteoglycan/[14C]collagen-coated plates to evaluate their capacities for proteoglycan and collagen degradation. The various macrophage populations differed widely in their potentialities for proteoglycan and particularly, for collagen degradation, native collagen being significantly degraded, in this model only by rabbit alveolar macrophages. Fibroblasts were as active in proteoglycan degradation as the most active macrophage preparations, but their potential for collagen degradation appeared much higher than that of macrophages. Moreover, all types of macrophages secreted a factor, a monokine, that activated collagen and proteoglycan degradation by fibroblasts. Thus, fibroblasts might well be a major effector cell, active in connective tissue degradations occurring under chronic inflammatory situations.