Polysaccharide A (PSA) is a polysaccharide produced by the Gram-negative bacterium Bacteroides fragilis.[1] B.fragilis produces eight identified distinct capsular polysaccharides, identified by the letters "A" through "H".[2]
PSA colonization of B. fragilis in the gut mucosa induces regulatory T cells and suppresses pro-inflammatory T helper 17 cells.[2] PSA has been shown to protect animals from experimental diseases like colitis, asthma, or pulmonary inflammation.[2] Nonetheless, PSA can be pro-inflammatory as well as anti-inflammatory.[3]