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Lancet. 1999 Sep 18;354(9183):1000-1.

Inverse association between BCG immunisation and intestinal nematode infestation among HIV-1-positive individuals in Uganda.


Exposure to infections in infancy may induce a sustained bias in the immune response. In our study, previous BCG immunisation was associated with a reduced prevalence of intestinal nematode infection.


The inverse association between Bacillus Calmette-Guerin (BCG) immunization and intestinal infestation among HIV-1 positive individuals in Uganda was studied. Stool samples from 103 participants who were similar in age, sex, and BCG immunization status were examined for ova and parasites. The most significant finding was the low incidence of nematode infestation among individuals who had BCG immunization. The association of BCG immunization in childhood with lower prevalence of intestinal nematode infestations in HIV-1 positive adults was similar among participants with low and high CD4-cell counts. It was further expounded that mycobacteria, including BCG, typically elicit type-1 immune responses, whereas allergens and helminths elicit type-2 responses. These two types of responses are mutually inhibitory. This led to a hypothesis that BCG immunization during infancy contributes to a lasting type-1 bias in the immune response, thus reducing susceptibility to helminths. Evidence that type-1 responses are protective against filariae supports this hypothesis. Meanwhile, recent opinion concerning intestinal nematodes points out that type-2 responses are beneficial, at least against adult worms.

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