Characterisation of the CD4+ T cell response to Epstein-Barr virus during primary and persistent infection

The CD8(+) T cell response to Epstein-Barr virus (EBV) is well characterized. Much less is known about the evolution of the CD4(+) T cell response. Here we show that EBV stimulates a primary burst of effector CD4(+) T cells and this is followed by a period of down-regulation. A small population of EBV-specific effector CD4(+) T cells survives during the lifelong persistent phase of infection. The EBV-specific effector CD4(+) T cells accumulate within a CD27(+) CD28(+) differentiation compartment during primary infection and remain enriched within this compartment throughout the persistent phase of infection. Analysis of CD4(+) T cell responses to individual epitopes from EBV latent and lyric cycle proteins confirms the observation that the majority of the effector cells express both CD27 and CD28, although CD4(+) T cells specific for lyric cycle antigens have a greater tendency to express CD45RA than those specific for the latent antigens. In clear contrast, effector CD4(+) T cells specific for cytomegalovirus (CMV) accumulate within the CD27(-) CD28(+) and CD27(-) CD28(-) compartments. There are striking parallels in terms of the differentiation of CD8(+) T cells specific for EBV and CMV. The results challenge current ideas on the definition of memory subsets.