Acquired resistance to Listeria monocytogenes is mediated by Lyt-2+ T cells independently of the influx of monocytes into granulomatous lesions.

Facultative intracellular bacteria induce specific T cell responses of both the CD4+ and the CD8+ subsets. The immunohistological study of the tissue responses to Listeria monocytogenes in T cell subset-depleted, Listeria-primed mice revealed that CD4+ cells not only represent the predominant lymphocyte population in granulomatous lesions but mediate the attraction and accumulation of blood-borne monocytes into inflammatory foci. On the other hand, CD8+ T cells are able to mediate protection in the absence of CD4+ T cells, invading monocytes, and granulomatous inflammation, and therefore appear to activate resident macrophages for listericidal activity.