Long-lasting tumor immunity requires functional mobilization of CD8+ and CD4+ T lymphocytes. CD4+ T cell activation is enhanced by presentation of shed tumor antigens by professional antigen-presenting cells (APCs), coupled with display of similar antigenic epitopes by major histocompatibility complex class II on malignant cells. APCs readily processed and presented several self-antigens, yet T cell responses to these proteins were absent or reduced in the context of class II+ melanomas. T cell recognition of select exogenous and endogenous epitopes was dependent on tumor cell expression of γ-interferon–inducible lysosomal thiol reductase (GILT). The absence of GILT in melanomas altered antigen processing and the hierarchy of immunodominant epitope presentation. Mass spectral analysis also revealed GILT's ability to reduce cysteinylated epitopes. Such disparities in the profile of antigenic epitopes displayed by tumors and bystander APCs may contribute to tumor cell survival in the face of immunological defenses.

We have reported that lung allograft rejection involves an immune response to a native protein in the lung, type V collagen (col(V)), and that col(V)-induced oral tolerance prevented acute and chronic rejection. In support of these findings col(V) fragments were detected in allografts during rejection, but not in normal lungs. The purpose of the current study was to isolate and characterize col(V)-specific allograft-infiltrating T cells and to determine their contribution to the rejection response in vivo. Two col(V)-specific T cell lines, LT1 and LT3, were isolated from F344 (RT1lv1) rat lung allografts during rejection that occurred after transplantation into WKY (RT1l) recipients. Both cell lines, but not normal lung lymphocytes, proliferated in response to col(V). Neither LT1 nor LT3 proliferated in response to alloantigens. LT1 and LT3 were CD4+CD25− and produced IFN-γ in response to col(V). Compared with normal CD4+ T cells, both cell lines expressed a limited V-β TCR repertoire. Each cell strongly expressed V-β 9 and 16, but differed in expression of other V-βs. Adoptive transfer of each cell line did not induce pathology in lungs of normal WKY rats. In contrast, adoptive transfer of LT1, but not LT3, caused marked peribronchiolar and perivascular inflammation in isograft (WKY) lungs and abrogated col(V)-induced oral tolerance to allograft (F344) lungs. Collectively, these data show that lung allograft rejection involves both allo- and autoimmune responses, and graft destruction that occurs during the rejection response may expose allograft-infiltrating T cells to potentially antigenic epitopes in col(V).

Peptides bind cell surface MHC class II proteins to yield complexes capable of activating CD4+ T cells. By contrast, protein Ags require internalization and processing by APC before functional presentation. Here, T cell recognition of a short peptide in the context of class II proteins occurred only after delivery of this ligand to mature endosomal/lysosomal compartments within APC. Functional and biochemical studies revealed that a central cysteine within the peptide was cysteinylated, perturbing T cell recognition of this epitope. Internalization and processing of the modified epitope by APC, was required to restore T cell recognition. Peptide cysteinylation and reduction could occur rapidly and reversibly before MHC binding. Cysteinylation did not disrupt peptide binding to class II molecules, rather the modified peptide displayed an enhanced affinity for MHC at neutral pH. However, once the peptide was bound to class II proteins, oxidation or reduction of cysteine residues was severely limited. Cysteinylation has been shown to radically influence T cell responses to MHC class I ligands. The ability of professional APC to reductively cleave this peptide modification presumably evolved to circumvent a similar problem in MHC class II ligand recognition.

In this paper, we have tested the efficacy of a recently developed nonperturbative open-shell formalism in generating such difference energies as ionization potential (I. P.), electron affinity (E. A.) and excitation energy (E. E.). In the formalism, the difference energies come out directly as eigenvalues of a non-Hermitian eigenproblem. Two different kinds of cluster expansion about multideterminant ‘‘model’’ wave functions have been considered: (a) an ordinary Ursell–Mayer type exponential form of cluster expansion; and (b) a normally ordered exponetial cluster ansatz. The key theoretical concept underlying our development is a generalization of the ‘‘core-valence separability’’ concept of the open-shell manybody perturbation theory which we have termed the ‘‘subsystem embedding condition’’ (SEC). SEC allows us to start with the zero valence problem and offers an unambiguous way of building up the successive one, two, ..., n-valence problems hierarchically furnishing the difference energies. I. P., E. A., and E. E. of a selection of nitrogen heterocycles under the π-electron approximation have been calculated and the performance of the methods has been assessed against the ‘‘model exact’’ full CI results. The trend of the results has been found to be encouraging.

Regulatory T cells (Tregs) induced by oral tolerance may suppress immunity by production of TGF-β that could also enhance Treg activity. However, all cells that are phenotypically Tregs in rats (CD4+CD45RChigh-RChigh) may not have regulatory function. Because Smad7 expression in T cells is associated with inflammation and autoimmunity, then lack of Smad7 may identify those cells that function as Tregs. We reported that feeding type V collagen (col(V)) to WKY rats (RT1l) induces oral tolerance to lung allografts (F344-RT1lvl) by T cells that produce TGF-β. The purpose of the current study was to identify the Tregs that mediate col(V)-induced tolerance, and determine Smad7 expression in these cells. RChigh cells from tolerant rats were unresponsive to allogeneic stimulation and abrogated rejection after adoptive transfer. In contrast, CD4+CD45RClow (RClow) cells from tolerant rats and RChigh or RClow cells from normal rats or untreated allograft recipients proliferated vigorously in response to donor Ags, and did not suppress rejection after adoptive transfer. TGF-β enhanced proliferation in response to col(V) presented to tolerant RChigh, but not other cells. In contrast to other cells, only RChigh cells from tolerant rats did not express Smad7. Collectively, these data show that the Tregs that mediate col(V)-induced tolerance to lung allografts do not express SMAD7 and, therefore, are permissive to TGF-β-mediated signaling.

Knowledge of the events governing Ag processing and epitope selection within APC is key to the development of novel immunotherapeutic strategies for infectious diseases, cancer, and autoimmunity. The influence of disulfides and Ag reduction on the hierarchy of epitope presentation via MHC class II molecules was investigated through studies of a self Ag, IgG κ. HLA-DR4+ B cells preferentially present an immunodominant IgG-derived epitope, κI, relative to a subdominant κII peptide. κI contains a cysteine masked within the native Ag via an intrachain disulfide, the latter of which is reduced during Ag processing. Mutagenesis of this cysteine as well as others within κ minimally perturbed the abundance and overall conformation of IgG. Yet, disruptions in disulfide bonding within this Ag influenced the selective display of class II-restricted dominant and subdominant T cell epitopes. Presentation of the κI epitope from both native and variant IgG was dependent upon cellular expression of IFN-γ-inducible lysosomal thiol reductase. These studies indicate that disulfide bonds regulate Ag processing both locally and at distant sites, thus influencing epitope selection within the class II pathway.

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Oral administration of mycobacterial 65-kDa heat shock protein (HSP) given daily for 5 days prior to immunization with Mycobacterium tuberculosis (Mt) suppressed the development of adjuvant arthritis (AA) in rats. AA was significantly suppressed by 30 and 300 micrograms HSP, and variably by 0.3, 3 micrograms or 1 mg. Histological analysis of joint samples obtained from control and test rats confirmed the suppression of AA in the fed group. Feeding Mt or hen egg lysozyme (HEL) failed to affect AA, indicating that the suppression was HSP specific. The oral administration of 30 micrograms HSP decreased both delayed-type hypersensitivity (DTH) reactions and proliferative responses to HSP and Mt. In addition, the proliferation of lymph node cells (LNC) from Mt-sensitized rats was inhibited by the addition of spleen cells (SPC) from HSP-fed animals, possibly by the secretion of transforming growth factor (TGF)-beta. Spleen cells obtained from tolerized donors were capable of transferring the tolerance to naive recipients. These results demonstrate that feeding HSP is an effective way to suppress AA and that the suppression of AA may be mediated by regulatory T cells generated following oral administration of mycobacterial 65-kDa HSP.