The immune response against the intracellular bacterium Listeria monocytogenes involves both CD4(+) and CD8(+) T cells. We used the MHC class II-presented peptide listeriolysin(189-201) to characterize the organ-specific CD4(+) T cell response during infection. Systemic listeriosis resulted in a strong peptide-specific CD4(+) T cell response with frequencies of 1/100 and 1/30 CD4(+) splenocytes at the peak of primary and secondary response, respectively. This response was not restricted to lymphoid organs, because we detected specific CD4(+) T cells in all tissues analyzed. However, the tissue distribution of the T cell response was dependent on the route of infection. After i.v. infection, the strongest CD4(+) T cell response and the highest levels of memory cells were observed in spleen and liver, the major sites of L. monocytogenes replication. After oral infection, we detected a strong response in the liver, the lamina propria, and the intestinal epithelium. These tissues also harbored the highest frequencies of listeriolysin(189-201)-specific CD4(+) memory T cells 5-8 wk post oral infection. Our results show that kinetics and magnitude of the CD4(+) T cell response and the accumulation of CD4(+) memory T cells depend on the route of infection and are regulated in a tissue-specific way.
