Construction of novel in vitro epithelioid cell granuloma model from mouse macrophage cell line

There have been several attempts to make granuloma model to clarify the mechanism of granulomatous diseases like sarcoidosis. However, a unique in vitro model that generates multinucleated giant cell (MGC) through epithelioid cells resembled to human granuloma, has not yet been clearly established. In this study, the generation of granuloma model that forms MGC via epithelioid cells from the mouse macrophage cell line was investigated. A RAW 246.7 mouse macrophage cell line was cultured with lipopolysaccharide (LPS) and concanavalin A (Con A) in various concentrations either alone or both. We found that separate treatment of LPS and Con A induced around 35 and 20% MGC respectively whereas cotreatment of these chemicals drastically accelerated granuloma formation rate and it was around 80%. The highest fusion index (MGC formation rate) was observed at days 7. A gradual increase of tumor necrosis factor alpha (TNF-alpha) production in the culture supernatant was analyzed by enzyme-linked immunosorbent assay (ELISA). And the neutralization of the elevated level of TNF-alpha production by its monoclonal antibody leads to significant decrease of MGC formation. Interestingly, we found that the RAW cells were changed into spindle cells, which morphologically resembled to epithelioid cells and eventually MGC was formed from these spindle cells. Our in vitro granuloma model appeared to be similar with in vivo epithelioid cell granulomas like sarcoidosis. Thus, our model would be useful as in vitro epithelioid granuloma model for analyzing the mechanisms and screening the effective drugs of granulomatous diseases in future.