HYALURONIC-ACID INDUCES TUMOR-NECROSIS-FACTOR-ALPHA PRODUCTION BY HUMAN MACROPHAGES IN-VITRO

Foetal wounds heal with minimal or no scar formation. High levels of h yaluronic acid (HA) have been implicated as a contributory factor. Mac rophages are essential for normal wound healing, a role facilitated by secretion of an array of cytokines. Of these, tumour necrosis factor alpha (TNF-alpha) has been shown to reduce wound collagen levels and t hus scarring. This study examines the ability of HA to stimulate TNF-a lpha production by human macrophages. The human U937 myelomonocytic ce ll line was differentiated into DU937 adherent macrophages. DU937 mono layers were exposed to HA at concentrations of 0.1, 1, 10 and 100 mu g /ml. Conditioned media from HA-exposed monolayers were assayed for TNF -alpha activity using a standard L929 fibroblast bioassay. TNF-alpha a ctivities of HA-exposed DU937 culture supernatants were compared to th ose of controls and expressed as % cytotoxicity. Exposure of macrophag es to HA at concentrations of 10 mu g/ml and 100 mu g/ml significantly stimulated TNF-alpha production, as demonstrated by % cytotoxicities expressed as median (interquartile range) of 33.5 (29-34.5)% (P = 0.03 ) and 77.5 (67-85)% (P = 0.029) respectively (Mann-Whitney Utest). Thi s effect was specifically associated with TNF-alpha generated during H A exposure, as these cytotoxic effects could be abolished by addition of anti-TNF-alpha antibody, reducing cytotoxicity to 9 (6.5-13.5)% and 8.5 (6-12)% respectively. These observations indicate that HA stimula tes TNF-alpha production by human macrophages. TNF-alpha is known to d ownregulate fibroblastic collagen synthesis within experimental wounds . We suggest that the high levels of HA within foetal wounds may play a part in limiting fibroplasia, and thereby limit scarring, via an upr egulation of TNF-alpha production from wound macrophages.