Regulatory networks induced by live parasites impair both Th1 and Th2 pathways in patent lymphatic filariasis: implications for parasite persistence.

Babu, S.; Blauvelt, C.P.; Kumaraswami V.; Nutman, T.B.

The Journal of Immunology; 2006; 176; 3248–3256.

Patent lymphatic filariasis is characterized by a profound down-regulation of immune responses with both parasite Ag-specific tolerance and bystander suppression. Although this down-regulation is confined to the Th1 arm of the immune system in response to parasite Ag, we hypothesized a more generalized suppression in response to live parasites. Indeed, when we examined the cytokine profile of a cohort of filaria-infected ( n = 10) and uninfected ( n = 10) individuals in response to live infective-stage larvae or microfilariae of Brugia malayi , we found significant impairment of both Th1 and Th2 cytokines characterized by diminished production of IFN- g , TNF- a , IL-4, IL-5, and IL-10 in infected patients. The molecular basis of this impaired Th1/Th2 response was examined, and we identified three major networks of immunoregulation and tolerance. First, impaired induction of T-bet and GATA-3 mRNA underlies the Th1/Th2 deficiency in infected individuals. Second, regulatory networks, as evidenced by significantly increased expression of Foxp3 (natural regulatory T cell marker) and regulatory effectors such as TGF- b , CTLA-4, PD-1, ICOS, and indoleamine 2,3-dioxygenase play an important role in immunosuppression. Third, the compromise of effector T cell function is mediated by the enhanced induction of anergy-inducing factors cbl-b , c-cbl ( cbl is abbreviation for Casitas B lymphoma), Itch , and Nedd4 . Indeed, blocking CTLA-4 or neutralizing TGF- b restored the ability to mount Th1/Th2 responses to live parasites and reversed the induction of anergy-inducing factors. Hence, we conclude that a profound impairment of live parasite-specific Th1 and Th2 immune responses occurs in lymphatic filariasis that is governed at the transcriptional level by a complex interplay of inhibitory mediators.

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