Budowa i znaczenie II systemu sekrecji białek w ekologii i patogenezie Legionella pneumophila

Legionella pneumophila bacilli parasitize in the cells of phylogenetically distant hosts: protozoa in the aquatic environment and alveolar macrophages in the human body. The ability of these bacteria to multiply intracellularly in phagocytic cells specialized to destroy microorganisms is critical to the development of atypical pneumonia known as Legionnaires' disease. Located at several different loci of the bacterial chromosome, the genes of the type II secretion system of L. pneumophila encode at least 25 proteins, including enzymes with lipolytic, proteolytic, and ribonuclease activity and proteins that are unique for Legionella. In the natural environment, the T2SS system of L. pneumophila plays a decisive role in the ecology of these microorganisms, determining their ability to survive in freshwater reservoirs at low temperatures, both in planktonic form and in biofilm structures. T2SS proteins enable L. pneumophila to infect various species of protozoa, and the substrates of this system determine the extent of the protozoan host. The multiplication of bacteria in a wide range of protozoa contributes to their dissemination and transmission to anthropogenic sources. Proteins secreted by the type II secretion system also determine the ability of L. pneumophila to infect murine alveolar macrophages and bone marrow, human macrophages of the U937 and THP-1 lines, and alveolar epithelial cells. Enzymes secreted by this system, such as proteases, aminopeptidases or phospholipases, contribute to the destruction of lung tissue, in the mouse model of pneumonia. In the human body, T2SS proteins contribute to the reduction of the innate immune response to L. pneumophila infection by inhibiting the induction of pro-inflammatory cytokines (IL-6, TNF-α, IL-1, and IL-8).