Innate immune lectins kill bacteria expressing blood group antigen A century ago Landsteiner demonstrated that blood group antigen ABO(H) expression differs between individuals. The expression of ABO(H) causes deletion of cells that generate self anti-blood group antibodies, which permits transfer of blood products between immunologically compatible individuals. However, this cellular deletion results in a gap in the adaptive immune response toward pathogens bearing cognate blood group antigens. The mechanism of overcoming these gaps in adaptive immunity is unknown. Here we report that two innate immune galectins specifically recognize and kill human blood group B antigen-expressing E. coli, while failing to alter viability of other E. coli strains or other gram-negative or gram-positive organisms. Killing by both galectin-4 and galectin-8 resides entirely within their Cterminal domains and occurs independent of complement, providing specific innate immunity against blood group B positive pathogens regardless of an individual’s blood group status. These results demonstrate that specific innate defense lectins exist that can provide immunity against pathogens that display blood group selfantigens on their surface.