Acid proteases of vitreal macrophages

Macrophage invasion in rabbits was elicited by intravitreal injection of trypan blue or latex particles; as after hemorrhage, there are two periods of macrophage invasion with elevated numbers of intravitreal cells at three and 21 days. Release of acid proteolytic activity by macrophages from both time periods was assayed by analysis of the cell-free vitreal supernate and of the medium of cultured cells. Lysates of freshly-isolated macrophages and of adjacent ocular tissues were also analyzed. Although some quantitative differences were observed, a similar profile of acid proteolytic activity toward hemoglobin at pH 2.0 to 6.5 was found in the vitreal supernate and in the cells from both periods. Most macrophages invade via the ciliary processes and during invasion elevated levels of acid proteolytic activity were found in this tissue. Although some macrophages transmigrate the retina, normal acid protease levels were low in sensory retina and essentially unchanged during macrophage invasion. Protease inhibitor studies indicated the presence of carboxyl, cysteinyl, serine and metallo proteases in macrophages and in macrophage-containing tissues. The inhibitor data also suggested qualitative differences in acid protease activities in macrophages from the two invasive periods. During macrophage invasion vitreal pH was reduced from 7.4 to 6.2 suggesting that some macrophage-derived acid proteases may be active in that compartment. Thus, although the phagocytic activity of macrophages aids vitreal clearing, action of macrophage proteases may also contribute to vitreal pathology by cleavage of vitreal proteins.