Expression of intracellular IFN-gamma in HSV-1-specific CD8(+) T cells identifies distinct responding subpopulations during the primary response to infection

Cutaneous infection in the footpads of C57BL/6 mice with HSV-1 results in a n accumulation of activated (CD44(high) CD25(+)) CD8(+) T cells within the draining popliteal lymph node (PLN), These studies were undertaken to evalu ate the frequency and phenotype of the CD8(+) T cell population within the PLN, recognizing the single immunodominant HSV-1 epitope derived from the v iral envelope glycoprotein, glycoprotein B (gB), using an intracellular IFN -gamma-staining assay. It revealed that similar to 6% of the CD8(+) T cells were specific for the gB epitope, Phenotypic analysis of the IFN-gamma-pro ducing gB-specific CD8(+) T cells generated in the PLN during the course of the acute infection expressed the CD44(high) CD25(+) phenotype on days 3-5 postinfection. Surprisingly, IFN-gamma-producing CD8(+) T cells expressed the CD44(high) CD25(-) phenotype on days 5-8 postinfection, in contrast to expectations for a CD8(+) effector T cell. IFN-gamma-producing CD25(-) CD8( +) T cells were detected in the PLN on day 21 postinfection, long after inf ectious virus had been cleared. Throughout the response, the spleen was fou nd to be the major reservoir of gB-specific CD8(+) T cells, even during the peak of the response. In contrast to the gB-specific CD8(+) T cell populat ion within the PLN, the entire gB-specific CD8(+) T cell population within the spleen was CD25(-). Collectively, these results suggest the generation of subpopulations of virus-specific CD8(+) T cells, distinguished by the ex pression of CD25, during the acute phase of the primary response to a local ized viral infection.