The peak of CD4+IL-2+ responses following KOS infection on day 14 PI was greater than responses to D22 (ICP22 null) virus infection (79.4% vs. 64.5%, P < 0.01) and was reduced on day 28 PI (60.5% vs. 36.2%, P < 0.001; Fig. 5A). Here, CD4 is linked to infection.