CD4 and viral infectious disease: In contrast, while CD4+IFN-γ+ responses were greater following KOS infection than D22 (ICP22 null) virus infection on day 14 PI (61.7% vs. 23.2%, P < 0.001), the differences between these viruses were not statistically significant on day 28 PI (35.6% vs. 27.5%, P > 0.05; Fig. 5C).