Salmonella Typhi flagellin (FliC (for the phase 1 flagellin in S. Typhi; FljB refers to phase 2 flagellin in other Salmonella serovars))

Flagellin is the main structural protein of the flagellar filament in Salmonella Typhi, responsible for bacterial motility and key interactions with the host. Each filament is made of thousands of flagellin subunits, arranged to form a long whip-like appendage[1]. In Salmonella Typhi, the flagellin gene is monophasic (encodes only FliC), unlike biphasic strains such as S. Typhimurium, which encode both FliC and FljB. Flagellin mediates motility, but also facilitates host cell invasion and influences the expression of other virulence factors, particularly the Salmonella pathogenicity island 1 (SPI-1) secretion system[3]. Besides its structural function, flagellin is recognized by host immune receptors (TLR5), triggering a strong inflammatory response[3]. Flagellin is among the best-known bacterial antigens (“H antigen”) and is exploited as a target for immunological detection, vaccine development, and as an adjuvant. In S. Typhi, flagellin is crucial for virulence, colonization, and modulation of immune responses, though it does not appear to be directly targeted by approved antimicrobials; rather, it is a tool and target for immunoprophylaxis and diagnostics[1][3]. Safety concerns with flagellin-based therapeutics stem from its inherent ability to induce robust inflammation[3].

Other names

FlagellinFliC (phase 1)H antigenSalmonella flagellar antigen

Immune activation: flagellin is recognized by Toll-like receptor 5 (TLR5) on host cells, leading to pro-inflammatory signaling; Vaccine/adjuvant: purified flagellin or flagellin fragments can be used to boost immune responses