The mechanism of Streptococcus avoiding immune system

According to a study published in the cell report on December 3, a bacterial pathogen that causes diseases such as streptococcal pharyngitis can hide itself in red blood cell fragments to avoid detection of the host immune system The researchers found that group A streptococcus (gas) produces an atypical protein called s protein The protein binds to the erythrocyte membrane to avoid phagocytosis and destruction by phagocytic immune cells Through this form of immune camouflage, S protein enhanced bacterial toxicity and reduced the survival rate of infected mice "Our study describes a new immune escape mechanism." "We believe that this previously overlooked discovery of the toxic factor s protein could help develop strategies against gas," said David Gonzalez of the University of California, San Diego Gas is a human specific pathogen, which can cause many different infections, such as streptococcal laryngitis, scarlet fever and so on It is estimated that 700 million people around the world are infected with the pathogen every year, resulting in more than 500000 deaths Despite active research by scientists, protective vaccines are still hard to find So far, penicillin is still the first choice drug to fight against GAS infection But in some parts of the world, the failure rate of penicillin treatment has risen to nearly 40% Another way is to develop new antiviral therapies To solve this problem, Gonzalez and colleagues Igor wierzbicki and anaamika campeau used biomimetic viromics technology to identify proteins secreted by gas and bound to red blood cells They found a previously unidentified protein, the S protein, because this type of protein exists only in members of the genus Streptococcus The researchers found that mutant strains lacking s protein had weaker ability to grow in human blood and to bind to red blood cells than those without s protein Mutants are also more easily captured and killed by phagocytic immune cells called macrophages and neutrophils In addition, the absence of S protein greatly reshaped the structure of bacterial protein and reduced the abundance of many known pathogenic factors In addition, the mortality rate of mice infected with gas cells coated with red blood cells was 90%, while that of mice without red blood cells was 40% "These findings suggest that s proteins work with red blood cell membranes to simulate molecules, or mimic host molecules, to evade immune responses," Gonzalez said Currently, the Gonzalez team is studying the mechanism of S protein binding to red blood cells and its role in other human pathogens, including Streptococcus pneumoniae, group B Streptococcus or Streptococcus lactis Streptococcus lactis is a common cause of severe infection in the first week of life.