Itch^−/− αβ T cells are required for elevated IgM and autoimmune antibodies but dispensable for hyper-IgE. (A) No production of antinuclear antibodies was detected by ELISA in sera of TCRa^−/− or TCRa^−/−Itch^−/− mice. Mice are divided in 2 age groups: 1 to 3 and 4 to 7 months of age. (B) Analysis of total Igs by ELISA from preimmune TCRa^−/− WT, TCRa^−/−Itch^−/+, and TCRa^−/−Itch^−/− mice shows no significant difference among the groups for most of the isotypes. (C) However, IgE is substantially elevated in Itch^−/− mice. (D) Ag-specific Igs in TCRa^−/− WT, TCRa^−/−Itch^+/−, and TCRa^−/−Itch^−/− mice immunized with TNP-Ficoll were equivalent. (E) The average (± SD) numbers of total peritoneal B-cell subpopulations from TCRa^−/− WT (□; n = 8), TCRa^−/−Itch^+/− (; n = 8), and TCRa^−/−Itch^−/− (■; n = 18) mice are shown. Subpopulations were identified by flow cytometry as follows: B2 = IgD^hiIgM^lo; B1 = IgM^hiIgD^lo; B1a = Mac1⁺CD5⁺; and B1b = Mac1⁺CD5⁻.