The Ra-reactive factor (RARF) is a complement-dependent bactericidal factor that binds to the Ra and R2 polysaccharides expressed by certain enterobacteria. Alternate splicing of this gene results in two transcript variants encoding two RARF components that are involved in the mannan-binding lectin pathway of complement activation. The longer isoform is cleaved into two chains which form a heterodimer linked by a disulfide bond. The encoded proteins are members of the trypsin family of peptidases.