Figure 1. Immunodominant mouse collagen type II peptide mCII_707–721 is CD1d restricted and activates CD4⁺TCRαβ⁺ NKT cells.

(A) Significant proliferative response was observed after in vitro peptide stimulation of LNCs from mCII_707–721–immunized mice (WT B10.Q). Controls are medium or control peptide mCI_707–721. Proliferation index (PI) was calculated by normalizing all cpm values to media control as 1. (B) PI in response to mCII_707–721 in KO mice, all B10.Q background. Proliferation was significantly reduced compared with WT littermates in Tcrab^–/–, CD4^–/–, and CD1d^–/– mice, indicating that the mCII_707–721 peptide response depends on CD1d-restricted CD4⁺TCRαβ⁺ T cells, but not classical MHC I/II presentation. (C) PI in response to mCII_707–721 in B10.Q LNCs. Blocking with anti–MHC II and anti–MHC I antibodies produced similar levels of PI compared with mCII_707–721 with control antibody. PI was calculated by normalizing all cpm values to media control as 1. (D) In vitro rechallenge response to mCII_707–721, abrogated by anti-CD1 (1B1, 10 μg/ml) or anti-NK1.1 (PK136, 10 μg/ml), indicating that CD1d-dependent NKT cells were operative in the response. PI was calculated by normalizing all cpm values to media control as 1. Data are mean ± SD, n = 6. **P ≤ 0.01; ***P ≤ 0.001.