ROLE OF INTERLEUKIN-6 IN THE INDUCTION OF PROTECTIVE T-CELLS DURING MYCOBACTERIAL INFECTIONS IN MICE

Interleukin-6 (IL-6) has been shown to regulate numerous functions of the immune system including the differentiation of T-cell subpopulatio ns. Here we examined the involvement of this cytokine in the in vivo g eneration of a population of T cells able to protect mice against myco bacterial infections. BALB/c mice were infected intravenously with Myc obacterium avium 2447 and anti-IL-6 monoclonal antibodies were adminis tered intraperitoneally throughout the course of the infection. Contro l mice were able to control the mycobacterial proliferation 1 month af ter inoculation, whereas mice whose IL-6 had been blocked showed progr essive bacterial growth. To distinguish a role for IL-6 associated to the induction or expression of immunity mediated by T cells, we immuni zed mice with M. bovis bacillus Calmette-Guerin (BCG) Pasteur and chal lenged them 2 months later with M. avium. One group of mice received a nti-IL-6 during the BCG vaccination and another during the M. avium ch allenge. When M. avium proliferation was assessed at day 30 of the cha llenge, it was found that the administration of anti-IL-6 during vacci nation reduced the protection afforded by BCG compared to administrati on of the isotype control antibody. No difference in bacterial prolife ration was observed at day 30 of challenge when antibodies were admini stered during M. avium challenge. Our results show that protective T c ells arise during M. avium infections in mice after differentiating in the presence of IL-6.