Cytokine regulation of C3 and C5 production by human corneal fibroblasts

Abstract

Recent investigations have suggested that cytokines play important roles during inflammation and host defense, primarily by regulating the diverse functions of immunologic cells (e.g. lymphocytes and monocytes). However, much less is known about the capacity of cytokines to also regulate the functions of resident tissue cells. We hypothesize that during inflammation, cytokines (e.g. monokines and lymphokines) directly regulate the expression of inflammatory precursors and mediators, such as the third and fifth complement components, by resident ocular cells and are therefore important in the local regulation of ocular inflammation. To test this hypothesis we developed an in vitro culture system utilizing isolated human corneal fibroblasts and examined the effects of specific cytokines, i.e. interleukins and interferons, on the production of the third and fifth components of the complement system. Human corneal fibroblasts were cultured in the presence of varying concentrations (1–500 U ml −1) of interleukin 1α, interleukin 1β, interleukin 2, interferon α and interferon γ for 48 hr at 37°C, 5% CO 2. The supernatants were then evaluated for antigen levels for the third and fifth components of complement using specific enzyme-linked immunospecific assays. These studies revealed that both interleukin 1α and interleukin 1β induced seven to tenfold increases in the levels of the third component. Similarly interferon α and interferon γ stimulated an approximate four and ninefold dose-dependent increase, respectively, in the production of the third component. Analysis of the effect of interleukin 2 on third component production demonstrated that higher concentrations (100 U ml −1) were required to induce a fivefold increase in the production of the third component. These same cytokines also increased production of the fifth component by human corneal fibroblasts, but to a lesser extent, i.e. 50–200% increase in the levels of the fifth component. These data demonstrate that both monokines (i.e. interleukin 1α and interleukin 1β) and lymphokines (i.e. interleukin 2, interferon α and interferon γ) are able to stimulate significant increases in third and fifth component production by human corneal fibroblasts in vitro. Thus, it is likely that cytokine-induced increases in third and fifth component production by corneal fibroblasts play an important role in the regulation of inflammation and host defense within the avascular cornea.