In injury and inflammation, complement (C) component Clq, in addition to its central role in initiation of classical pathway of complement activation, modulates diverse cellular functions by binding to specific cell surface receptors. Interaction of substrate-bound C l q with receptors for the collagen-like domain of C l q (ClqRC) of human gingival fibroblasts (HGF) promotes cell attachment. We investigated modulation of the adhesive function and expression of ClqRC by interleukin-1 p (IL-1 p) and transforming growth factor-@ (TGF-@I. Confluent fibroblast monolayers were incubated under standard culture conditions with or without cytokines. ClqRC function was measured by attachment assays. IL-lp and TGF-P increased fibroblast adhesion to C l q to 146% and 131 % of controls, respectively. Cytokine enhancement of HCF adhesion was concentration-dependent, saturable (20 ng/ml IL-1 p; 1 n g m l TGF-0) and time-dependent (IL-1 p 12-hr peak; TGF-P 24-hr peak). Effect of IL-1 p and TGF-P on C1 qRC expression was assessed by flow cytometry measurements of fluorescence intensity of cells stained with C1 q and FlTC anti-Clq antibody, and by binding studies with 'L51-Clq. Cells treated with cytokines displayed a twoto four-fold increased fluorescence of cell-bound C l q compared to controls. Binding studies indicated the increased fluorescence correlated with increase in number of ClqRC in both IL-1 p (4.7 x 1 O"/cell) and TGF-f3 (3.9 x 1o6/cell)-treated cells, compared to control (3.0 x 10"/cell), but had no effect on binding affinity. Rates of internalization of receptor-bound C l q were similar in cytokine-treated cells and controls. We propose from these data that IL-1 p and TCF-P have the ability to upregulate ClqRC expression, and this effect contributes to increased adhesion of HGF to substrate-bound C l q .