The CD8+ T-cell phenotype and functional capacity in β3−/− mice is partly reminiscent of exhausted T-cells in chronic viral infection as shown by the activated phenotype, impaired proliferative capacity and diminished cytokine production, although the cardinal marker for exhaustion PD-1 is not upregulated in β3−/− CD8+ T-cells (42, 43, 46). Here, CD8A is linked to viral infectious disease.