Yersinia pestis F1 antigen (F1 antigen)

The **Yersinia pestis F1 antigen** is a surface capsular protein uniquely produced by the plague bacterium Yersinia pestis at mammalian body temperatures (≈37°C). It is a high-molecular-weight polymer composed solely of Caf1 subunits, assembled on the bacterial surface via the chaperone/usher pathway encoded by the caf operon (caf1, caf1M, caf1A, caf1R)[2][4][5][6][7][9]. The F1 capsule forms a fibrous layer around the bacterium, functioning primarily as a virulence factor that impedes phagocytosis by host immune cells, thereby facilitating immune evasion and enhancing pathogenicity[1][2][4]. It is a potent immunogen, capable of inducing strong antibody responses which make it a key component in subunit, recombinant, and fusion vaccines against bubonic and pneumonic plague[9][10]. F1 antigen (alone or as part of fusion proteins, e.g., rF1-V) is widely used in vaccine efforts and basic immunological assays for the diagnosis or immunomonitoring of plague[9][10]. There are no significant direct safety concerns with the antigen itself beyond standard vaccine considerations.

Other names

F1 capsule antigenFraction 1 antigenCaf1 antigenF1 capsular antigen

Immune system stimulation (vaccination: F1 antigen induces rapid protective humoral and B cell responses against Y. pestis)[9] Antibody-mediated opsonization (naturally occurring or vaccine-induced antibodies promote bacterial clearance by phagocytosis)[1][9]