It is important to gain a better understanding of IL-1-mediated signaling events in mycobacterial infection. In order to clarify the role of IL-1 receptor type 1 (IL-1 R1) in IL-1 R1, knockout (KO) mice were infected with either Mycobacterium tuberculosis H37Rv or Kurono strain by the respiratory route, and their ability to control mycobacterial growth, pulmonary granuloma formation, and cytokine mRNA expression was investigated. IL-1 R1 KO mice developed significantly larger (P< 0.01) granulomatous lesions with neutrophil infiltration in their lungs than wild-type mice did after infection with the M. tuberculosis Kurono strain. The number of mycobacterial colonies in lungs and spleen increased from five weeks post-infection. Interferon-y production by spleen cells was low in IL-1 R1 KO mice. It is concluded that the IL-1 R1 is essential for IL-1-mediated signaling events in mycobacterial infection.