Depression of cell-mediated immune reactions during viral infection has been a repeatedly confirmed phenomenon since the original observation of von Pirquet (20). Reports have included depression of tuberculin activity in man following viral infection or vaccination (2,3,12,16,19) as well as prolongation of allograft survival in virus-infected mice (14). Numerous investigations have indicated that virus-induced Type I interferons can modulate cell-mediated immune responses. These also include inhibition of the development of delayed-type hypersensitivity to tuberculin and sheep red blood cells (6,7) and prolongation of skin allograft survival in mice (13).
