The recombinant LigB7′-12 protein that we have characterized as an adhesin in L. interrogans along with other functions that could mediate early host interactions in the transmission of leptospirosis also binds C3b with high avidity, exhibiting an apparent Kd of 43±26 nM (n = 6; Figure 2A). This evidence concerns the gene C3 and leptospirosis.