Microbiota: its contribution to carcinogenesis and immunity in the lungs

Microbiota (an assembly of bacteria, protists / archaea, fungi, and viruses inhabiting a human body) is currently of great interest for science. It is determined by an association between changes in microbiota composition and malignant transformation in different organs. Lungs have long been considered sterile or free from bacteria; however, due to development of next-generation sequencing, this statement has been reconsidered. The metagenomic approach allowed to identify microorganisms at molecular level both in healthy lung tissues and in malignant ones. The next stage of research is investigation of the effects of microbiota on homeostasis and immune stability in the lungs. The analysis of lung microbiota based on 16S rRNA gene sequencing revealed that microbiota of healthy lungs is mainly presented by bacteria of the phyla Bacteroidetes, Firmicutes, Proteobacteria, and Fusobacteria. In lung cancer, an increase in the number of bacteria of some certain genera and a decrease in microbiota diversity on the whole are noted. Dysbiosis facilitates reproduction of pathogens and development of lung diseases. It was detected that under normal conditions, microbiota maintains resistance of the lungs to bacterial colonization and plays a crucial role in providing a balanced immune response in this organ.