Substantial in vivo proliferation of CD4+ and CD8+ T lymphocytes during secondary Listeria monocytogenes infection

In mice Listeria monocytogenes infection induces a strong T cell response. In an attempt to quantitatively analyze the magnitude and kinetics of the CD4+ and CD8+ T cell response during L. monocytogenes infection in vivo we used a T cell transfer system that is independent of in vitro cell culture techniques and information about the identity of immunogenic T cell epitopes. Our results demonstrate substantial expansion of the in vivo primed and transferred T cell populations in response to L. monocytogenes. At the peak of response, transferred T cells represented more than one third of the total CD4+ and CD8+ T cell populations in blood and spleen of recipient mice. After stimulation in vitro, 40 % of these CD4+ T cells responded to heat‐killed listeriae with the production of IFN‐γ. Thus, our results reveal that in addition to the large CD8+ T cell population an almost equally large population of Listeria‐reactive CD4+ T cells is generated in response to L. monocytogenes infection.