The gut–lung axis in tuberculosis

The gut–lung axis allows for the passage of microbial products, endotoxins and metabolites, as well as hormones and cytokines into the bloodstream connecting the intestinal niche with that one of the lung. The gut–lung axis is bidirectional, as a lung–gut axis also exists when the inflammatory phenomenon occurring in the lung can cause alterations in the blood and gut microbiota. Metabolic diseases such as diabetes, malnutrition, antibiotic usage, parasitic infection and the immunogenetic background of the host can affect the immune response to Mycobacterium tuberculosis (Mtb) infection, as well as causing changes in the lung microbiota. Recent evidence shows that the presence of specific species of the genus Helicobacter may play a role in the outcome of Mtb infection as well. The commensal bacterium Helicobacter hepaticus may increase susceptibility to Mtb infection, while H. pylori may confer protection against tuberculosis disease. The protective role of the intestinal microbiota against lung infections could open the door to new therapeutic and immunization strategies.