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The MHC class II molecule DQ0602 confers strong susceptibility to narcolepsy but dominant protection against type 1 diabetes. The crystal structure of DQ0602 reveals the molecular features underlying these contrasting genetic properties. Structural comparisons to homologous DQ molecules with differential disease associations highlight a previously unrecognized interplay between the volume of the P6 pocket and the specificity of the P9 pocket, which implies that presentation of an expanded peptide repertoire is critical for dominant protection against type 1 diabetes. In narcolepsy, the volume of the P4 pocket appears central to the susceptibility, suggesting that the presentation of a specific peptide population plays a major role.

β2integrin molecules are involved in a multitude of cellular events, including adhesion, migration, and cellular activation. Here, we studied the influence of β2integrins on interleukin-2 (IL-2)-mediated signal transduction in human CD4+T cell lines obtained from healthy donors and a leukocyte adhesion deficiency (LAD) patient. We show that IL-2 induces tyrosine phosphorylation of a 125-kDa protein and homotypic adhesion in β2integrin (CD18)-positive but not in β2-integrin-negative T cells. EDTA, an inhibitor of integrin adhesion, blocks IL-2-induced tyrosine phosphorylation of the 125-kDa protein but not other proteins in β2-integrin-positive T cells. Likewise, a β2integrin (CD18) antibody selectively inhibits induction of the 125-kDa phosphotyrosine protein, whereas cytokine-mediated tyrosine phosphorylation of other proteins is largely unaffected. Immunoprecipitation experiments indicate that the IL-2-induced 125-kDa phosphotyrosine protein is the focal adhesion kinase-related protein B (fakB). Thus, IL-2 induces strong tyrosine phosphorylation of fakB in β2-integrin-positive but not in β2-integrin-negative T cells, and CD18 mAb selectively blocks IL-2-induced fakB-tyrosine phosphorylation in β2-integrin-positive T cells. In parallel experiments, IL-2 does not induce or augment tyrosine phosphorylation of p125FAK. In conclusion, our data indicate that IL-2 induces β2-integrin-dependent signal transduction events involving the tyrosine kinase substrate fakB.

Mycosis fungoides (MF) is a low-grade cutaneous T cell lymphoma of unknown etiology. In this report, the Jak/Stat (Janus kinase/signal transducer and activator of transcription) signaling pathway was investigated in tumor cell lines established from skin biopsy specimens from a patient with MF. Jaks link cytokine receptors to Stats, and abnormal Jak/Stat signaling has been observed in some hemopoietic cancers. In MF tumor cells, a slowly migrating isoform of Stat3, Stat3 sm , was found to be constitutively activated, i.e., ( i ) Stat3 sm was constitutively phosphorylated on tyrosine residues, and tyrosine phosphorylation was not enhanced by growth factor stimulation; ( ii ) band shift assays and immunoprecipitations of DNA/Stat complexes showed constitutive DNA-binding properties of Stat3 sm ; and ( iii ) Stat3 sm was constitutively associated with Jak3. The abnormal activation of Stat3 sm was highly specific. Thus, neither the fast migrating isoform of Stat3 (Stat3 fm ) nor other Stats (Stat1, Stat2, and Stat4 through Stat6) were constitutively activated. The Jak kinase inhibitor, tyrphostin AG490, blocked the constitutive activation of Stat3 sm and inhibited spontaneous as well as interleukin 2-induced growth of MF tumor cells. In conclusion, we have provided evidence for an abnormal Jak/Stat signaling and growth regulation in tumor cells obtained from affected skin of an MF patient.

A cytotoxic T lymphocyte (CTL) clone generatedin vitrofrom the peripheral blood of a healthy HLA-A2-positive individual against a synthetic p53 protein-derived wild-type peptide (L9V) was shown to kill squamous carcinoma cell lines derived from two head and neck carcinomas, which expressed mutant p53 genes, in a L9V/HLA-A2 specific and restricted fashion. Thus, the normal tolerance against endogenously processed p53 protein-derived self-epitopes can be broken by peptide-specificin vitropriming. p53 protein-derived wild-type peptides might thus represent tumor associated target molecules for immunotherapeutical approaches.

Cytotoxic T cells recognize mosaic structures consisting of target peptides embedded within self-major histocompatibility complex (MHC) class I molecules. This structure has been described in great detail for several peptide-MHC complexes. In contrast, how T-cell receptors recognize peptide-MHC complexes have been less well characterized. We have used a complete set of singly substituted analogs of a mouse MHC class I, Kk-restricted peptide, influenza hemagglutinin (Ha)255-262, to address the binding specificity of this MHC molecule. Using the same peptide-MHC complexes we determined the fine specificity of two Ha255-262-specific, Kk-restricted T cells, and of a unique antibody, pSAN, specific for the same peptide-MHC complex. Independently, a model of the Ha255-262-Kk complex was generated through homology modeling and molecular mechanics refinement. The functional data and the model corroborated each other showing that peptide residues 1, 3, 4, 6, and 7 were exposed on the MHC surface and recognized by the T cells. Thus, the majority, and perhaps all, of the side chains of the non-primary anchor residues may be available for T-cell recognition, and contribute to the stringent specificity of T cells. A striking similarity between the specificity of the T cells and that of the pSAN antibody was found and most of the peptide residues, which could be recognized by the T cells, could also be recognized by the antibody.

The tetrameric HLA antigens are composed of two heavier chains which carry the alloantigenic determinants and two lighter chains identified as beta2-microglobulin. Although at least 40 different antisera are required to define the varying HLA specificities, it appears that these antigens may be closely related to each other and to the immunoglobulins. Through the use of a new electrophoretic technique, which is able to compare simultaneously the tyrosine peptides produced from radioiodinated cell surface proteins, this report gives evidence that HLA antigens of the three chromosomal loci may have similar amino-acid sequences. Since the retention of homologous tyrosine residues and a tendency for sequence preservation surrounding these residues are features of immunoglobulin structure, this may indicate that similarly conservative evolutionary mechanisms have been operative in the HLA allelelic proteins or that immunoglobulins and HLA antigens may indeed have a common evolutionary origin.

Sequences of different sizes are generated when DNA from homozygous HLA-Dw/DR typing cells are digested with restriction endonuclease and analyzed by hybridization with a HLA-D region class II antigen beta-chain cDNA probe. The patterns of hybridization were highly polymorphic but one endonuclease, BamHI, defined sequences unique to all HLA-Dw/DR specificities 1-8 except HLA-Dw/DR 2 and 6; however, these two specificities were resolved with the enzyme EcoRI. Digestion with other endonucleases such as Pst I results in patterns of restriction fragments that differ between homozygous typing cells of the same HLA-Dw/DR specificity. HLA-D region beta-chain probes permit HLA-D region genotyping at the DNA level and may allow detection of genes controlling the association of HLA specificities with a wide variety of diseases.

The restriction fragment length polymorphism (RFLP) of the class II HLA-DP subregion of the major histocompatibility complex (MHC) of humans has been unraveled by Southern blotting using DP alpha and DP beta probes in a study of 46 unrelated individuals with known HLA-DP types. Contrary to earlier preliminary findings with a limited number of enzymes, the RFLP appears to be quite extensive both with the DP beta (14 different DNA markers defined by individual fragments or clusters thereof) and the DP alpha (8 markers) probes, especially when enzymes recognizing only four base pairs were used. A few markers were absolutely or strongly associated with individual DP antigens, whereas most were associated with two or more DP antigens as defined by primed lymphocyte typing. Thus, Southern blotting seems feasible for typing for most DP determinants by specific fragments or subtraction between the various more broadly reactive DNA markers, and the RFLP provides further information on the DP subregion in addition to that provided by primed lymphocyte typing. In two recombinant families, the DP beta and DP alpha DNA markers segregated with DP antigens, whereas the DR beta, DQ beta, DQ alpha, and DX alpha markers followed the DR and DQ antigens.