Transition from interleukin 1 beta (IL-1 beta) to IL-1 alpha production during maturation of inflammatory macrophages in vivo.

In situ production of interleukin 1 alpha (IL-1 alpha) and IL-1 beta was investigated in Peyer's patches (PP) of mice undergoing an acute bacterial infection with Yersinia enterocolitica O8. Synthesis of IL-1 beta, as determined by immunohistochemistry, was found primarily in monocytes migrating into the inflamed PP. In comparison, synthesis of IL-1 alpha was temporarily delayed by at least 24 h and was only found in mature macrophages, which did not produce detectable levels of IL-1 beta. This indicates a transition from IL-1 beta to IL-1 alpha production during maturation of monocytes into inflammatory macrophages, and further emphasizes a dichotomy between IL-1 alpha and IL-1 beta.