A compound produced by the immune system triggers the recruitment of immune cells during an infection, but only with the proper signaling from other immune cells. However, recent research findings show that certain bacterial species can also activate the same compound.
Interleukin-1beta (IL-1beta) is first produced by the immune system as a long and inactive compound that requires cleavage for activation. While the body uses the inflammasome to cleave and activate IL-1beta, Group A Streptococcal bacteria produces its own enzyme called SpeB to do the same, which scientists from the University of California San Diego found in their recent study, published in the journal Science Immunology
While it might seem counterintuitive that natural selection would favor a bacterial species that practically warned the host’s immune system of its presence, researchers from the study believe that the technique is to “wipe out competing bacteria” so Streptococcus can enter and dominate.
First author Christopher LaRock, PhD said it also makes sense to for bacteria to inhibit SpeB production: “This finding may explain why some of the more invasive, flesh-eating strep strains have a genetic mutation that blocks SpeB production; it helps them avoid tripping the alarm and setting off an immune response.”
LaRock and the team analyzed data from a U.S. Food and Drug Administration database, looking for rheumatoid arthritis patients with extreme infections who also were known to be taking anakinra, an immunosuppressant drug that works by inhibiting IL-1beta activity. According to their findings, rheumatoid arthritis patients taking the drug were 300 times more likely than patients not taking the drug to experience “invasive, flesh-eating strep infections” from Group A Streptococcus species.
“With IL-1beta out of the picture, as is the case with patients taking anakinra, strep strains can progress to invasive infection while producing SpeB, which goes unnoticed by the immune system," LaRock said.
This study simultaneously revealed how vital IL-1beta is to effective immune protection and how important it is for doctors to consider doses and types of immunosuppressive drugs they give to patients. Rheumatoid arthritis is one of many autoimmune disorders that occur because of an overreaction of the immune system. While drugs that inhibit IL-1beta might help with flares of rheumatoid arthritis, infections with intense flesh-eating bacteria aren’t the right solution either. Doctors have to find a balance, including “close-monitoring and prophylactic antibiotics.”
Source: University of California San Diego