CD4 and viral infectious disease: The CD4+IL-4+ cytokine response following KOS virus infection was elevated on day 14 PI, compared to D22 (ICP22 null) virus infection (21.6% vs. 6.9%, P < 0.001), but differences between these groups were not significant on day 28 PI (3.9% vs. 10%, P > 0.05; Fig. 5B).