C1q inhibits the expression of B lymphoblastoid cell line interleukin 1 (IL 1)

Although the existence and ubiquity of the C1q receptor is well established, its role in health and disease is largely unknown. Interleukin 1 (IL 1) is the major immunoregulatory molecule produced by macrophages and B lymphoblastoid cell lines. In this paper we present evidence that occupancy of C1q receptors by C1q on B lymphoblastoid cell lines inhibits 'Il 1-like' activity, which is constitutively produced by these cells. When 5 x 10⁶ Raji cells were cultured (24 hr at 37° C) in the presence or absence of various concentrations of C1q (final concentration; 5 to 50 μg/ml) and the cellfree supernatants were analyzed for their effect on thymocyte proliferation by using the concanavalin A co-mitogenesis assay for IL 1, a statistically significant dose-dependent reduction of ³H-TdR incorporation was observed. Similar results were obtained when Daudi and Wil₂WT cells were used, whereas Molt₄, which is a T cell lymphoblastoid cell line, neither produced 'IL 1-like' activity nor was affected by C1q. When immune complex-bound C1q was used instead of free C1q, inhibition of B cell IL 1 activity was also observed. Mixing experiments showed that Raji cels incubated with C1q released an inhibitor of IL 1-induced thymocyte proliferation. C1q alone had no effect on thymocyte proliferation in the presence or absence of human IL 1. In addition, the effect of C1q on IL 1 activity was abrogated either when the C1q was heat inactivated (56° C, 60 min) or when the C1q was incubated with the cells in the presence of F(ab')₂ anti-C1q. On the basis of these data, it is concluded that B cell receptor-bound C1q may play an important role in immunoregulation.