An updated model of cell-mediated immunity--listeriosis: clinical and research aspects.

Listeria monocytogenes causes sepsis and meningitis in immunocompromised hosts and a devastating maternal/fetal infection in pregnant women. In recent years a more benign gastroenteritis in normal hosts has been described. Listeria has been increasingly identified as a food-borne pathogen, and large-scale contamination of processed foods with resulting outbreaks has occurred in recent years, possibly as a result of consolidation of the food industry. Experimental listeriosis in mice has proven to be an extraordinarily useful model for analyzing cell-mediated immune host defenses. Contrary to original concepts, we found that neutrophils, not macrophages, are the prime effectors during early infection. CD8+ T cells are then responsible for lysing infected hepatocytes through perforin-related (early primary and secondary infection) or Fas-L/Fas mechanism (late primary). Of interest, non-classical MHC class Ib restricted recognition mechanisms exist early, whereas MHC class Ia mechanisms can be detected throughout infection.