T cell reactivity to Listeria monocytogenes amongst us

In the last two decades, listeriosis, caused by the intracellular pathogen Listeria monocytogenes, became one of the most concerning food-born infections. Although it had been known before as an infectious disease of limited importance, listeriosis was brought into attention of scientists due to the frequent outbreaks recently reported. Despite the major progress made towards understanding the mechanisms of virulence of L. monocytogenes, our current knowledge into the process of Listeria-associated pathogenesis and virulence is still partial and fragmentary. In this study we demonstrate that T lymphocytes with reactivity to L. monocytogenes are frequently present in healthy individuals (73%), most probably as a consequence of subclinical infections. Host resistance to infection by L. monocytogenes involves a series of interactions between cells of the immune system, of which the antigen presenting cell/T lymphocyte partnership is essential. The ability of memory T cells to respond when exposed to their target antigen is traditionally assessed by measuring uptake of [3H] - thymidine. Our study has been carried out by means of an alternative methodology based on flow-cytometry, an approach which has several advantages on [3H] - thymidine incorporation technique: allows targeted analysis of particular cell types, simultaneous assessment of various cellular markers, and circumvents handling of radioisotopes.