GAPDH and infection: RNA was isolated at multiple time points post-infection and the following RNAs were quantified: glyceraldehyde-3-phosphate dehydrogenase (GAPDH), as a control gene used for normalization, Tat, to correct for possible differences in infectivity, and a subset of ISG that includes IP-10, TRAIL, MCP-2, and HuMig that were observed modulated in the microarray expression analysis.