Effects of gamma-interferon on human trabecular meshwork cell phagocytosis

Gamma-interferon (G-IFN) regulates a variety of immune responses including the modulation of the phagocytic response and induction of class II major histocompatibility complex antigens. Because human trabecular meshwork (HTM) cells in culture are known to be actively phagocytic and have been shown to express class II major histocompatibility complex antigens, the effects of G-IFN on HTM cells were examined.

Confluent HTM cells were incubated in media (Dulbecco's modified Eagle's medium +10% fetal bovine serum) containing 0, 10, 50, 100, 500, 1000, or 5000 units/ml of recombinant human G-IFN for 72 hr. After incubation, the cultured HTM cells were challenged with 5 ml of media containing 1 x 10(8) fluorescein labeled microspheres/ml. Phagocytic uptake was determined by flow cytometry.

Flow cytometric analysis of microsphere uptake shows that G-IFN inhibited HTM cell phagocytosis of microspheres in a dose-dependent fashion. At 5000 units/ml of G-IFN, phagocytosis of microspheres was inhibited by 64.5 +/- 2.4% compared to control (P < 0.007). The half maximal dose of phagocytic inhibition is < 10 units/ml. Increasing the time of G-IFN exposure from 24 to 72 hr at 10 units/ml increased the level of phagocytic inhibition from 39 to 49%, respectively. The rate of microsphere uptake was also reduced in a dose-dependent fashion. Morphologic examination after G-IFN incubation showed that HTM cells became enlarged and flattened compared to the control. Actin cytoskeletal immunofluorescence staining showed that parallel actin beams of the control cells were changed to a radical, spokelike arrangement when incubated in G-IFN.

G-IFN is a potent inhibitor of HTM cell phagocytosis in vitro. G-IFN's effect on the actin cytoskeleton suggests that G-IFN may be disturbing the cytoskeletal organization necessary for phagocytosis.