Do Mycobacteria protect against asthma and allergy?

Mycobacteria are typical inducers of a preferential Th1-type cytokine response. Thus, they are discussed as possible modifyers of Th2-dependent allergic disease. Here we review the currently available data from both experimental and epidemiological studies. Murine studies indicate that infection with BCG prevents allergic sensitization, airway inflammation, and airway hyperreactivity. Moreover, BCG can downregulate preexisting allergic sensitization. Epidemiological studies indicate an inverse association of tuberculosis notification rates and prevalences of allergic diseases. Some studies demonstrate an inverse relationship of PPD-reactivity and atopy whereas in other studies this finding could not be replicated. In contrast, most epidemiological studies show no association of BCG-vaccination and prevalence of atopy. Preliminary results suggest that a therapeutic effect of non-pathogenic mycobacteria may be possible. The currently available data, however, do not allow recommendation of mycobacterial antigens as a prophylactic or therapeutic option in allergy.