Isolation, Synthesis, and Antimicrobial Activities of Naturally Occurring θ-Defensin Isoforms from Baboon Leukocytes▿

θ-Defensins are macrocyclic antimicrobial peptides that were previously isolated from leukocytes of a single species, the rhesus macaque. We now report the characterization of baboon θ-defensins (BTDs) expressed in bone marrow and peripheral blood leukocytes. Four cDNAs encoding θ-defensin precursors were characterized, allowing for the prediction of 10 theoretical θ-defensins (BTD-1 to BTD-10) produced by binary, head-to-tail splicing of nonapeptides excised from paired precursors. Five of the predicted θ-defensins were purified from baboon leukocytes, and synthetic versions of each were prepared. Anti-θ-defensin antibody localized the peptides in circulating neutrophils and monocytes and in immature and mature myeloid elements in bone marrow. Each of the BTDs possessed antimicrobial activity against bacterial and fungal test organisms in vitro. Peptide activities varied markedly despite a high degree of sequence conservation among the θ-defensins tested. Thus, baboons express numerous θ-defensins which appear to differentially contribute to host defense against diverse pathogens