The Immune Response to Toxocariasis Does Not Modify Susceptibility to Mycobacterium tuberculosis Infection in BALB/c Mice

Abstract

Mycobacterium tuberculosis and helminth infections coincide geographically and are classically described as TH1 and TH2 pathologies. There is much interest in exploring how concurrent worm infections might alter immune responses to mycobacterial infection. To explore this issue, mice were infected with Toxocara canis and co-infected with M. tuberculosis. Mice infected with M. tuberculosis had high numbers of neutrophils and mononuclear cells within the alveolar spaces, with increased parenchymal interferon (IFN)-gamma levels. However, in Toxocara-infected mice we detected increased eosinophil numbers in bronchoalveolar lavage fluid (BALF) and increased parenchymal levels of interleukin (IL)-5. In co-infected mice the BALF demonstrated enhanced eosinophil influx with decreased neutrophil and mononuclear cell accumulation. However, co-infected mice had similar mycobacterial proliferation in their lungs accompanied by similar histopathological changes and similar cytokine/nitric oxide production compared with Mycobacterium-only-infected mice. Our results suggest that T. canis infection does not necessarily lead to increased susceptibility to pulmonary tuberculosis.

Incidence of Active Pulmonary Tuberculosis in Patients with Coincident Filarial and/or Intestinal Helminth Infections Followed Longitudinally in South India

“…Studies in mice showed that the presence of the intestinal helminth Nippostrongylus brasiliensis had no effect on Mycobacterium bovis bacillary load at either 4 or 12 weeks post infection compared with uninfected controls [19]. A Toxocara model with Mtb infection showed no differences in the IFN-γ response, bacterial loads, T cell proliferation, or histopathologic changes despite there being an alteration in the composition of the alveolar infiltrate[2]. More recently, cotton rats co-infected with the rodent filarial parasite Litomosoides sigmodontis and Mtb [20] showed no alteration in antigen-specific IFN-γ responses, PPD-specific T cell proliferation, or tissue bacillary loads of Mycobacteria in Mtb-infected rats.…”

“…According to WHO reports, 1·4 million deaths were associated with tuberculosis (TB) in 2010 worldwide [1], [2]. The 2010 worldwide tuberculosis (TB) incidence was 8·8 million (128 cases/100 000 inhabitants), of which 59% were detected in Asia.…”

Helminth-Tuberculosis Co-infection: An Immunologic Perspective

“…Despite these findings, there have been other studies in which there was little to no effect of pre-existing helminth infection on TB. In one mouse study, infection with Toxocara canis was not associated with increased susceptibility to pulmonary tuberculosis [85]. Similarly, mice co-infected with N. braziliensis and M. bovis BCG were able to clear the BCG infection at the same rate as the helminth-uninfected controls [86].…”

Harnessing the Helminth Secretome for Therapeutic Immunomodulators

“…However, some infections with parasitic worms like Nippostrongylus brasiliensis and Toxocara canis with Mycobacterium bovis or M. tuberculosis do not lead to an impaired protective immune response [22–24]. …”