B cells are the major MHC-II–expressing APCs in the blood presenting inulin peptides.(A) Blood leukocytes were obtained from 4-wk-old female NOD mice, and the MHC-II (I-A^g7)–bearing cells were analyzed by flow cytometry. Data show representative FACS plots depicting the gating strategy for identifying different APCs in the blood, including the MHC-II⁺ B cells, monocytes, pDCs, and conventional DCs. (B) Percentage of the MHC-II⁺ B cells, monocytes, pDCs, and conventional DCs, as described in A, among the total CD45⁺ leukocytes in the blood of 4-wk-old female NOD mice. (C) Responses of the InsB:13-21– and InsB:12-20–specific CD4 T cells to equal numbers of B cells or non–B cell APCs (regardless of MHC-II expression) isolated from NOD mice given glucose. (D) Responses of the InsB:13-21– and InsB:12-20–specific CD4 T cells to equal numbers of B cells or non–B cell APCs isolated from NOD mice (regardless of MHC-II expression) without glucose challenge upon pulse with exogenous InsB:9-23 (10 µM). Data (mean ± SEM) summarize results pooled from two (B–D) independent experiments; each point represents one biological replicate including three or four mice. *, P < 0.05; Mann–Whitney test. CPM, counts per minute.