CD4 and mumps infectious disease: To be able to detect measurable numbers of specific T cells, peripheral blood mononuclear cells (PBMCs) of eight mumps cases, of which one was homozygous and three were heterozygous for HLA-DRB1*04, were stimulated with the GTYR peptide in the presence of IL-2, and CD4+ T cell responses, as well as their cytotoxic phenotypes, were characterized after a 12-day expansion.