Presentation of viral antigens to T cells does not require uptake by ‘professional’ antigen-presenting cells. Viruses have specialized to enter the cells in which they replicate. Virus entry, uncoating and new viral protein synthesis can load both the cytosolic and the endosomal pathway of antigen processing, resulting in viral peptide presentation to CD8 and CD4 T cells by MHC class I and 11 molecules, respectively. Although a role of CD8 T cells in the control of viral infection has been well documented, current research interest centers on the contribution of the different CD4 T-cell subsets.