TNF and infection: The sequential characterization of cytokine responses during the first seven days following infection with Ab4 WT virus shows that increases in pro-inflammatory (IL-1, IFN-α, TNF-α), T-helper 1 associated (IFN-γ,) and regulatory cytokines (TGF-β and IL-10) coincide with the biphasic increases in body temperature and the onset of respiratory disease and viremia respectively.