Antifungal activity of macrophages engineered to produce IFNγ: Inducibility by picolinic acid

Macrophages are important antimicrobial effectors, whose efficacy is greatly enhanced by interferon- gamma (IFN gamma ). We recently engineered a mouse macrophage cell line to express the IFN gamma gene in a inducible manner. Such macrophages, M phi 10, include a construct containing the IFN gamma gene under the control of the synthetic promoter HRE3x-Tk. Picolinic acid (PA) is a catabolite of tryptophan, known to exert costimulatory activities on macrophages and expected to act on transcriptional elements within HRE3x-Tk promoter. Since evidence exists on the efficacy of engineered macrophages as carriers of therapeutic genes against tumors, we tested M phi 10, under basal conditions and following exposure to PA, as IFN gamma -producing cells in in vitro models of fungal infection. We found that M phi 10 constitutively exhibited anticryptococcal and anticandidal activity, low but detectable levels of IFN gamma mRNA and undetectable levels of nitric oxide synthase (iNOS) transcripts. Treatment with PA caused time-dependent enhancement of antifungal activity. The phenomenon was associated with the induction of both IFN gamma and iNOS gene expression and was followed by IFN gamma and NO production. The effect of the M phi 10-produced IFN gamma on other cells was also investigated by a transwell co-culture system. A major enhancement of phagocytosis and antifungal activity was observed in BV2 microglial cells that had been co-cultured with M phi 10. Such an increase was only evident when M phi 10 had been pretreated with PA and was abrogated by concomitant addition of anti-IFN gamma antibodies. In conclusion, we show that M phi 10 respond to PA with the production of IFN gamma , which retains the ability to induce antifungal activity in the producing macrophages as well as in other macrophage populations. The potential use of M phi 10 as vectors for therapeutic genes in infectious diseases is discussed.