An essential function of the innate immune system is to directly trigger antimicrobial mechanisms to defend against invading pathogens. In humans, one such pathway involves activation by TLR2/1L leading to the vitamin D-dependent induction of antimicrobial peptides. In this study, we found that TLR2/1-induced IL-15 was required for induction of CYP27b1, the VDR and the downstream antimicrobial peptide cathelicidin. Although both IL-15 and IL-4 triggered macrophage differentiation, only IL-15 was sufficient by itself to induce CYP27b1 and subsequent bioconversion of 25-hydroxyvitamin D3 (25D3) into bioactive 1,25D3, leading to VDR activation and induction of cathelicidin. Finally, IL-15-differentiated macrophages could be triggered by 25D3 to induce an antimicrobial activity against intracellular Mycobacterium tuberculosis. Therefore, IL-15 links TLR2/1-induced macrophage differentiation to the vitamin D-dependent antimicrobial pathway.