Cell Rep: how do Streptococcus escape recognition by the immune system?

December 5, 2019 / BIOON / -- a study published in the Journal of cell reports on December 3 shows that a pathogen causing streptococcal laryngitis and other related diseases "hides" itself in red blood cell fragments to avoid detection of host immune system The researchers found that group A streptococcus (gas) produced a previously unrepresentated protein, called s protein, which binds to the erythrocyte membrane to avoid phagocytosis and destruction by phagocytic immune cells By arming gas with this form of immune camouflage, S protein can enhance the toxicity of bacteria and reduce the survival rate of infected mice "Our study describes a new immune escape mechanism," said David Gonzalez, a communications author at the University of California, San Diego We believe that the discovery of this previously overlooked virulence factor s protein has broad implications for the development of therapies for gas " (image source: www Pixabay Com) gas is a human specific pathogen that can cause many different infections, ranging from mild to very severe and fatal diseases Some of these diseases include streptococcal laryngitis, scarlet fever, skin infections known as pustules, toxic shock syndrome, and carnivorous diseases It is estimated that 700 million infections occur every year around the world, resulting in more than 500000 deaths Despite active research, protective vaccines are still difficult to develop So far, penicillin is still the main drug of choice to fight against GAS infection But in some parts of the world, the failure rate of penicillin treatment has risen to nearly 40% "Because of the high prevalence of gas infection and the decline in the effectiveness of available therapies, it is important to study alternative approaches to gas infection," Gonzalez said To avoid immune clearance, gas expresses a variety of molecules called virulence factors to promote survival during infection However, the function of many of these proteins is still unknown To solve this problem, Gonzalez et al Used a nanotechnology, biomimetic virology, to identify the proteins secreted by gas and bound to red blood cells This method reveals a previously unidentified protein, which researchers call s protein, because the expression of this type of protein is limited to members of Streptococcus The researchers found that the mutant strain without s protein had weaker growth ability in human blood and weaker binding ability with red blood cells than the strain without s protein Mutants are also more easily captured and killed by macrophages and neutrophils In addition, the lack of S protein has greatly changed the appearance of bacterial protein and reduced the abundance of many known virulence factors In addition, mice infected with gas cells coated with red blood cells showed a 90% mortality rate, much higher than the 40% mortality rate of control mice In addition, the weight of mice in the experimental group also decreased rapidly "These findings suggest that s protein evades the immune response by selecting red blood cell membranes to mimic molecules or host molecules," Gonzalez said "In general, the results show that s protein affects the survival and infection of bacterial cells by capturing the dissolved erythrocyte membrane and covering the surface of bacterial cells," Gonzalez said This novel escape mechanism can be used as a target of anti streptococcal therapy Sources of information: how the Strep bacterium ides from the immune system: Igor H wierzbicki, anaamika campeau, Diana dehaini, Maya holay, Xiaoli Wei, Trever Greene, man Ying, Jenna S sands, Anne Lamsa, Elina Zuniga, kit pogliano, Ronnie h Fang, Christopher n Larock, Yangfang Zhang, David J Gonzalez Group A Streptococcal S Protein Utilizes Red Blood Cells as Immune Camouflage and Is a Critical Determinant for Immune Evasion Cell Reports, 2019; 29 (10): 2979 DOI: 10.1016/j.celrep.2019.11.001