Coordinated change between complement C1s production and chondrocyte differentiation in vitro

In vitro synthesis of the first component of complement C1s was examined by using hamster epiphyseal chondrocytes (HAC) and human chondrosarcoma cell line HCS-2/8. Hamster and human C1s produced by the cells were quantified by immunoblotting and sandwich enzyme-linked immunosorbent assay (ELISA), respectively. It was possible to measure active and inactive C1s by sandwich ELISA, when we used anti-human C1s monoclonal antibodies, M241 recognizing only active C1s, and M365 and M81 recognizing both active and inactive C1s. Approximately 40% of C1s secreted from HCS-2/8 was found to be activated in the culture medium, whereas C1s from HAC was not. C1s production increased in accordance with chondrocyte differentiation induced by ascorbic acid. In contrast, transforming growth factor-beta1 and basic fibroblast growth factor, which inhibited differentiation, suppressed C1s production. These results confirmed our previous observation showing that C1s synthesis increased with differentiation into hypertrophic chondrocytes in vivo.