Natural and vaccine-induced virus infections often are associated with depression of delayed-type hypersensitivity (DTH),' T-helper cell function, and the in vitro proliferative response of lymphocytes to antigens and phytohemagglutinin (1-3). The underlying mechanisms are complex and have not yet been fully elucidated. However, in certain myxoand paramyxovirus infections, unresponsiveness seem...