Transporters Associated with Antigen Processing (TAP)-independent Presentation of Soluble Insulin to α/β T Cells by the Class Ib Gene Product, Qa-1b

Abstract

T cell hybridomas isolated from nonresponder H-2b mice immunized with pork insulin were stimulated by insulin in the presence of major histocompatibility complex (MHC)-unmatched antigen presenting cells. The restriction element used by these CD4− T cells was mapped to an oligomorphic MHC class Ib protein encoded in the T region and identified as Qa-1b using transfectants. The antigenic determinant was localized to the insulin B chain, and experiments with truncated peptides suggested that it is unexpectedly long, comprising most or all of the 30 amino acid B chain. The antigen processing pathway used to present insulin to the Qa-1b– restricted T cells does not require transporters associated with antigen processing (TAP), and it is inhibited by chloroquine. A wide variety of cell lines from different tissues efficiently present soluble insulin to Qa-1b–restricted T cells, and insulin presentation is not enhanced by phagocytic stimuli. Our results demonstrate that Qa-1b can function to present exogenous protein to T cells in a manner similar to MHC class II molecules. Therefore, this class Ib protein may have access to a novel antigen processing pathway that is not available to class Ia molecules.

Dendritic Cells Use Endocytic Pathway for Cross-Priming Class Ib MHC-Restricted CD8αα+TCRαβ+ T Cells with Regulatory Properties

“…Cytotoxicity mediated by T cells was tested using a standard 4-h 51 Crrelease assay with minor modifications. Target cells (Con A-activated blasts) were labeled with 51 Cr (MP Biomedicals) at 37°C for 45 min (in complete DMEM medium).…”

“…Target cells (Con A-activated blasts) were labeled with 51 Cr (MP Biomedicals) at 37°C for 45 min (in complete DMEM medium). A total of 10,000/well 51 Cr-labeled targets and 200 ng/well peptides were added to round-bottom, 96-well plates. Plates were then incubated at 37°C with 10% CO 2 for 1 h. Effector cells (splenocytes from immunized mice or the CD8␣␣ ϩ TCR␣␤ ϩ T cell line XT-14; Ref.…”

“…A total of 150 l/well scintillation liquid (OptiPhase SuperMix; PerkinElmer) was added, and the sample plates were read on a Trilux scintillation gamma counter. Spontaneous 51 Cr-release was measured in control wells containing target cells with medium alone. Maximum release values were obtained by lysis of target cells with 2.5% Triton X-100 (Sigma-Aldrich).…”

Suppression of autoimmune disease after vaccination with autoreactive T cells that express Qa-1 peptide complexes

“…Both selection and antigen-recognition depend on expression of the TCRα/β and do not require NKG2 receptors (46). CD8 cells that recognize Qa-1 associated with the insulin peptide efficiently kill Qa-1-expressing lymphoblastoid target cells in the presence of intact soluble insulin, that is following transporter associated with antigen presentation-independent (TAP-independent) processing and presentation of insulin-derived peptide by Qa-1 on activated target cells (47). Possibly, Qa-1-restricted inhibitory activity of CD8 cells ( Figure 6) may likewise reflect in vivo elimination of activated CD4 cells that display Qa-1-peptide complexes.…”

Peptide-Independent Folding and CD8αα Binding by the Nonclassical Class I Molecule, Thymic Leukemia Antigen

“…These CTL recognize TL expressed in TAP-deficient RMAS and insect cell lines (12), consistent with peptide-independent recognition or presentation of unconventional Ags loaded on TL through a TAPindependent pathway. The latter possibility has precedent because Qa-1 can present insulin to TCR␣␤ T cells through a TAP-independent endosomal pathway (25). Peptide elution experiments with TL isolated from a radiolabeled cell line demonstrated the apparent presence of TL-associated peptides but no sequence information was obtained by Edman degradation, possibly because of peptide N-terminal modifications (8).…”