BENEFICIAL-EFFECTS OF INTERLEUKIN-6 IN NEONATAL MOUSE MODELS OF GROUP-B STREPTOCOCCAL DISEASE

Previous studies have shown that tumor necrosis factor alpha (TNF-alph a) plays a pathophysiologic role in sepsis induced in rat pups by grou p B streptococci (GBS). In this model, TNF-alpha is also partially res ponsible for the induction of interleukin-6 (IL-6). The present study was undertaken to investigate the role of IL-6 in neonatal BALB/c mice infected with type III GBS. The effect of anti-IL-6 monoclonal antibo dies and recombinant IL-6 on lethality and TNF-ar production was inves tigated. In mouse pups infected with GBS strain COH1, plasma IL-6 reac hed levels of 3,067 +/- 955 and 1,923 +/- 891 U/ml when measured at 22 and 48 h, respectively (P < 0.05 compared with uninfected controls). Pretreatment with 25 mu g of anti-IL-6 antibodies totally prevented th e increase in circulating IL-6 bioactivity at both 22 and 48 h after i nfection (P < 0.05). Treatment with anti-IL-6 also induced a moderate decrease in survival time of mice infected with lethal doses of strain s COH1 and COH31, as evidenced by increased lethality (P < 0.05) at 24 to 48 h but not at 96 h. Mouse recombinant IL-6 (12,500 U) given 6 h before challenge with strains COH1 and COH31 consistently increased su rvival time, as evidenced by decreased (P < 0.05) lethality at 48 to 7 2 h but not at 96 h. The effects of IL-6 pretreatment were dose depend ent, since no protection was observed with doses lower than 12,500 U. In addition, no effects on lethality were noted when IL-6 was given at the time of challenge or at later times. TNF-alpha elevations (P < 0. 05 compared with uninfected controls) were measured at 12, 22, and 48 h after challenge with strain COH1 (68 +/- 28, 233 +/- 98, and 98 +/- 34 U, respectively). Pretreatment with IL-6 significantly (P < 0.05) d ecreased plasma TNF-alpha levels at 12 and 22 h, with 55 and 69% inhib itions, respectively. Anti-IL-6 had an opposite effect, as evidenced b y a 145% increase (P < 0.05) in TNF-alpha levels at 48 h after challen ge. Collectively, our data are compatible with the hypothesis that IL- 6 is involved in negative feedback regulation of plasma TNF-alpha leve ls in experimental GBS sepsis. In this model, IL-6 pretreatment can in crease survival time. Future studies will be needed to investigate the mechanisms underlying this effect.