Infection with Toxoplasma gondii reduces established and developing Th2 responses induced by Nippostrongylus brasiliensis infection.

Oral infection of C57BL/6 mice with 100 cysts of the protozoan parasite Toxoplasma gondii results in the development of small intestinal Th1-type immunopathology. In contrast, infection with intestinal helminths results in the development of protective Th2-type responses. We investigated whether infection with the helminth Nippostrongylus brasiliensis influences the development of T. gondii-induced Th1 responses and immunopathology in C57BL/6 mice infected with T. gondii. Prior as well as simultaneous infection of mice with N. brasiliensis did not alter the course of infection with 100 cysts of T. gondii. Coinfected mice produced high levels of interleukin-12 (IL-12) and gamma interferon (IFN-gamma), developed small intestinal immunopathology, and died at the same time as mice infected with T. gondii. Interestingly, local and systemic N. brasiliensis-induced Th2 responses, including IL-4 and IL-5 production by mesenteric lymph node and spleen cells and numbers of intestinal goblet cells and blood eosinophils, were markedly lower in coinfected than in N. brasiliensis-infected mice. Similar effects were seen when infection with 10 T. gondii cysts was administered following infection with N. brasiliensis. Infection of C57BL/6 mice with 10 T. gondii cysts prior to coinfection with N. brasiliensis inhibited the development of helminth-induced Th2 responses and was associated with higher and prolonged N. brasiliensis egg production. In contrast, oral administration of Toxoplasma lysate prior to N. brasiliensis infection had only a minor and short-lived effect on Th2 responses. Thus, N. brasiliensis-induced Th2 responses fail to alter T. gondii-induced Th1 responses and immunopathology, most likely because Th1 responses develop unchanged in C57BL/6 mice with a prior or simultaneous infection with N. brasiliensis. Our findings contribute to the understanding of immune regulation in coinfected animals and may assist in the design of immunotherapies for human Th1 and Th2 disorders.

Mice deficient in nuclear factor of activated T-cell transcription factor c2 mount increased Th2 responses after infection with Nippostrongylus brasiliensis and decreased Th1 responses after mycobacterial infection.

Infection of nuclear factor of activated T-cell transcription factor c2 (NFATc2)-deficient mice with the helminth Nippostrongylus brasiliensis led to a distinct increase in interleukin-4 (IL-4) and IL-5 protein synthesis by lymph node and spleen cells and to elevated serum immunoglobulin E (IgE) levels in comparison to those seen with infected control mice. While IL-4, IL-5, and IL-13 mRNA expression was also enhanced in lymph node cells from the lungs of infected NFATc2(-/-) mice, the number of T cells secreting Th2-type lymphokines remained the same in mice infected with N. brasiliensis. In contrast, lymphocytes from NFATc2-deficient mice infected with Mycobacterium bovis BCG secreted less gamma interferon than lymphocytes from infected control mice. These findings indicate that NFATc2 is an activator of Th1 responses and a suppressor of Th2 responses in vivo.

Infection with the helminth Nippostrongylus brasiliensis does not interfere with efficient elimination of Mycobacterium bovis BCG from the lungs of mice.

Infection with Mycobacterium tuberculosis continues to be one of the major global health threats. Strong mycobacterium-specific Th1 immune responses correlate with protection, and decreased Th1 responses correlate with disease progression. In contrast, the impact of Th2 responses on the development of protective immune responses to mycobacteria remains unclear. To analyze whether ongoing Th2 responses present in the lung influence the development of a protective Th1 immune response to mycobacteria, we coinfected mice with the helminth Nippostrongylus brasiliensis and Mycobacterium bovis BCG. We found that the T cells from the lymph nodes of coinfected mice secreted significantly less gamma interferon than did the T cells from mice infected with M. bovis BCG after in vitro stimulation with purified protein from M. tuberculosis when 10(8) CFU of M. bovis BCG were used for the infection. This result indicates that the helminth infection reduced the Th1 immune response to the mycobacteria in the lung. However, mycobacterial clearance was not delayed in the coinfected animals. Importantly, the infection with BCG after the helminth infection did not reduce the helminth-induced Th2 response in the lung, ruling out the possibility that the lack of a reduction in bacterial clearance in the coinfected mice was due to a downmodulation of the helminth-induced Th2 response. Taken together, our results suggest that ongoing Th2 responses in the lung do not necessarily lead to increased susceptibility to mycobacterial infection.