Effect of deworming on human T cell responses to mycobacterial antigens inhelminth-exposed individuals before and after bacille Calmette-Guerin (BCG) vaccination

The protective efficacy of BCG vaccination against pulmonary tuberculosis ( TB) is highly variable in different populations. The reason remains to be e lucidated. This study aims to investigate the possible effect of intestinal helminths on the immune response to PPD in naturally immunized or BCG-vacc inated humans. The study population was assessed for helminthic infection a nd those found to be positive were randomly assigned to either an albendazo le treatment group or a control group who received a placebo. The immune re sponse to PPD was compared between the two groups. In addition, subjects wh o were tuberculin skin test-negative in both groups were BCG vaccinated and later on tested for PPD-specific responses. Albendazole induced eliminatio n/or reduction in intestinal worms resulting in a significant improvement i n T cell proliferation and in interferon-gamma production by peripheral blo od mononuclear cells (PBMC) stimulated with PPD. Moreover, BCG vaccination significantly improved PPD-specific immune responses in the treated group b ut not in the placebo group. The differences in the in vivo skin test respo nses were not significant. The data show that cellular immune responses to PPD are reduced in persons with concurrent helminthic infections, perhaps r eflecting a lowered resistance to mycobacterial infections. This could expl ain, at least in part, the reduced efficacy of BCG against TB in helminth-e ndemic areas of the world.