Neither primary nor memory immunity to Mycobacterium tuberculosis infection is compromised in mice with chronic enteric helminth infection

Previously we had reported that Nippostrongylus brasiliensis, a helminth with a lung migratory phase, affected host resistance against Mycobacterium tuberculosis infection through the induction of alternatively activated (M2) macrophages. Several helminth species do not have an obligatory lung migratory phase but establish chronic infections in the host that include potent immune downregulatory effects, in part mediated through induction of a FoxP3⁺ T regulatory cell (Treg) response. Treg cells exhibit duality in their functions in host defense against M. tuberculosis infection since their depletion leads to enhanced priming of T cells in the lymph nodes and attendant improved control of M. tuberculosis infection, while their presence in the lung granuloma protects against excessive inflammation. Heligmosomoides polygyrus is a strictly murine enteric nematode that induces a strong FoxP3 Treg response in the host. Therefore, in this study we investigated whether host immunity to M. tuberculosis infection would be modulated in mice with chronic H. polygyrus infection. We report that neither primary nor memory immunity conferred by Mycobacterium bovis BCG vaccination was affected in mice with chronic enteric helminth infection, despite a systemic increase in FoxP3⁺ T regulatory cells. The findings indicate that anti-M. tuberculosis immunity is not similarly affected by all helminth species and highlight the need to consider this inequality in human coinfection studies.