Yersinia pestis F1 capsule antigen (F1 antigen)

The Yersinia pestis F1 capsule antigen is a major surface component of the bacterium responsible for the plague. Encoded by the caf1 gene on the pFra plasmid, this protein is expressed and assembled into a large, gel-like capsule when the pathogen is exposed to mammalian body temperatures (37°C). Its primary biological role is to act as a potent antiphagocytic factor, preventing host immune cells such as macrophages and neutrophils from engulfing the bacteria, thereby facilitating systemic spread and high mortality. In the context of therapeutics and diagnostics, the F1 antigen is the most critical target for plague prevention and identification. It serves as the primary component of modern recombinant subunit vaccines (often paired with the V antigen) and is the basis for rapid diagnostic tests used in the field to detect Y. pestis in clinical samples. While highly conserved, the existence of naturally occurring or engineered F1-negative strains remains a significant challenge for vaccine efficacy and biodefense strategies.

Other names

Fraction 1 antigenCaf1 proteinCapsular antigen F1Yersinia pestis capsular proteinF1 protein

Induction of protective neutralizing antibodies that facilitate opsonophagocytosis and prevent bacterial dissemination.