F1 capsular antigen protein of Yersinia pestis (F1 antigen)

F1 capsular antigen protein of Yersinia pestis (F1 antigen) is a capsule-like protein polymer (main subunit Caf1, 15.5 kDa), produced at mammalian host temperatures (37°C), and encoded by the caf1 gene on the unique pFra plasmid. Its assembly relies on the chaperone/usher pathway (Caf1M chaperone, Caf1A usher, and Caf1R regulator). It forms noncovalently associated fibrils on the bacterial surface, providing antiphagocytic properties by shielding Y. pestis from receptor interaction and macrophage-mediated clearance. The F1 antigen is not essential for virulence but enhances plague lethality, high bacteremia, and efficiency of flea-borne transmission. It is the major molecular target for anti-plague vaccine development, elicits rapid T-cell-independent humoral immunity, and is a recognized immunogen for diagnostics and vaccine design. There are no approved therapeutic drugs directly targeting F1, though monoclonal antibody and subunit vaccine strategies remain in active development.

Other names

Fraction 1 antigenF1 capsuleCaf1 (structural subunit)F1 capsular protein

Vaccines: Elicit protective humoral immunity—rapid anti-F1 IgG and IgM antibody responses. Monoclonal antibodies: Passive transfer provides protection by opsonizing bacteria and promoting their phagocytosis.