Endogenous IgG affects the cell biology of RPE cells and involves the TLR4 pathway

RPE is a key component of the blood-ocular barrier (BOB) and is equipped with immunological molecules such as toll-like receptors (TLRs) and complement receptors, which together orchestrate the innate and adaptive immunity of the eye. Immunoglobulin G (IgG) in the aqueous humor and vitreous body has traditionally been thought to be derived from serum via transcytosis across the BOB. Our previous work validated production of endogenous IgG by RPE cells locally. However, the function and role of this IgG in the intraocular immunity is poorly understood.

After confirming IgG production in a human RPE cell line (ARPE-19) with immunofluorescence, in situ hybridization, and RT-PCR, we further investigated the function of endogenous IgG in RPE biology with MTS, flow cytometry, and cell invasion analysis after downregulation of IgG by siRNA. Involvement of the TLR4 pathway was also studied using Western blot, ELISA and confocal microscopy.

Endogenous IgG is crucial for support of proliferation, mitosis, migration, and inhibition of apoptosis of RPE. Moreover, production of endogenous IgG by RPE is regulated by the TLR4 pathway in a concentration- and duration-dependent manner, and IgG affects the activation of the TLR4 pathway in a synergistic manner. Activation of the FcγR I pathway and production of IL-10 could be induced by IgG derived from RPE.

These data suggest that endogenous IgG may be a molecule that is essential for the physiological function of RPE, and suggest IgG is important for regulating intraocular immune responses under physiologic and pathologic conditions.