Adjuvant effect of gamma-inulin is mediated by C3 fragments deposited on antigen-presenting cells

The adjuvant effect of gamma -inulin, a strong activator of the alternative complement pathway, is web-known, hut its exact mechanism is not revealed yet. Here, we show that macrophages, isolated from the peritoneal cavity of gamma -inulin-injected mice and used. as antigen-presenting cells, enhance the proliferation of antigen-specific T-cells up to 2.5-fold when compared with macrophages of non-treated animals, This effect is abrogated by the p resence of anti-C3 F(ab')(2) fragments and by prior decomplementation of th e donor animals with CVF, It is demonstrated that treatment of mice with th e adjuvant results in deposition of C3-fragments onto the surface of perito neal macrophages, as does in vitro incubation of the cells with gamma -inul in in the presence of fresh autologous serum. Prior incubation of macrophag es with gamma -inulin plus serum in vitro enhances subsequent C3 production . Because it has been shown earlier that CR1/2 expressed on activated T-cel ls and interacting with covalently bound C3-fragments plays an important ro le in the augmentation of the adaptive response, our present results reveal a mechanism that contributes to the adjuvant effect of gamma -inulin and p oint to a further link between innate and adaptive immunity.