Differences in specificity of "DPw2-specific" cytotoxic T cell clones revealed with HLA-mutant lines: evidence that non-DP HLA genes influence recognition by some clones

Evidence for discoordinate regulation of the HLA-DPB1 gene

Characterization of cell lines derived from patients with type II bare lymphocyte syndrome, a pathological state in which the constitutive and inducible expression of HLA class II antigens is lacking, has permitted the identification of several trans-acting factors involved in the coordinated regulation of HLA class II genes. Although an increasing body of evidence has pointed to the existence of a discoordinate regulation of HLA class II loci, the mechanisms underlying such regulation are essentially unknown. In the present study, 45.EM2, a mutant lymphoblastoid cell line with a new pattern of HLA discoordinate expression is characterized. 45.EM2 expresses HLA-DR and -DQ but fails to express HLA-DP. The absence of HLA-DP expression in 45.EM2 is the result of a transcriptional defect, leading to a lack of DPB1 mRNA. By contrast, DPA1 transcription in this LCL is not impaired. The characteristics of 45.EM2 described here suggest the existence of a specific trans-acting factor involved in the control of DPB1 gene expression.

T-Cell epitopes and human leukocyte antigen restriction elements of an immunodominant antigen of Blastomyces dermatitidis

Humans infected with the dimorphic fungus Blastomyces dermatitidis develop strong T-lymphocyte responses to WI-1, an immunodominant antigen that has been shown to elicit protective immunity in mice. In the present study, the T-cell epitopes of WI-1 and human leukocyte antigen (HLA) restricting elements that display them were investigated. Peripheral blood mononuclear cells (PBMC) from 37 patients with a confirmed history of blastomycosis were tested for a response to WI-1 in primary proliferation assays; PBMC from 35 (95%) responded. Six patients whose PBMC proliferated strongly in response to WI-1 (defined as a stimulation index greater than 50) were tested further for responses to subcloned, recombinant fragments of the antigen. These patients responded chiefly to sequences within the N terminus and the 25-amino-acid tandem repeat. Cloned CD4(+) T cells from an infected individual were used to delineate more precisely the peptide epitopes in the fragments and HLA restricting elements that present them. A majority of the T-cell clones recognized an epitope spanning amino acids 149 to 172 within the N terminus, displayed by HLA-DR 15. A minority of the clones, which have been shown to perform a cytolytic function in vitro, recognized an epitope in the tandem repeat displayed by HLA-DPw4, an uncommon restricting element. Tandem repeat epitopes required display by the beta chain of DPw4 heterodimers. Thus, human T cells with different functions in vitro also recognize distinct regions of WI-1, raising the possibility that HLA restricting elements that present them could modulate immunity during blastomycosis by selection and display of WI-1 peptides.

HLA-DPbeta residue 69 plays a crucial role in allorecognition

To investigate the contribution to allorecognition of the individual polymorphic positions Glu 69 and Val 36 from the DPB1*02012 allele, DPB1*02012 cDNA was subjected to site-directed mutagenesis and alleles expressing Lys at 69 and Ala at 36 were generated. The lymphoblastoid cell line (LCL) 45.EM1, a previously generated mutant B-LCL which expresses normal levels of DPA mRNA but is not able to transcribe DPB, was transfected with wild-type or mutant DPB1*02012 cDNAs. The ability of two HLA-DPw2 alloreactive CD4+ cytotoxic T-lymphocyte (CTL) clones to lyse the panel of DPB1*02012 wild-type and site-directed mutant B-cell lines was tested. Both CTL clones (8.3 and 8.9) lysed the B-LCL 45.1, which is haploid for HLA and expresses wild-type DPB1*02012, and transfectants expressing Ala at 36 instead of Val, indicating that this polymorphic residue is not critical for T-cell recognition. However, the change of Glu to Lys at 69 prevented recognition by clones 8.3 and 8.9. These data demonstrate that the residue at peptide-binding position 69 is crucial for T-cell receptor recognition and suggest the requirement for a negatively charged residue at this position for allostimulation of these T-cell clones. The side chain of DPbeta-69 is predicted to point into the peptide-binding groove, and the existence of positive(Lys) or negative (Glu) residues probably leads to substantial differences in the allo- or auto-DP-bound peptides or to differences in the conformation of the peptide-MHC complex, which would therefore be responsible for specific DPw2 allorecognition. The binding of a panel of monomorphic and polymorphic anti-HLA-DP monoclonal antibodies (mAbs) to these transfectants was also tested by flow cytometry. The changes at Glu 69 and Val 36 did not affect recognition by any of the monomorphic antibodies tested. However, the binding pattern of some of the polymorphic mAbs was clearly modified. Therefore, even though it is not crucial for T-cell allorecognition, polymorphic residue 36 must be involved in epitopes recognized by some polymorphic anti-DP antibodies, while residue 69 of the DPB molecule is crucial both for T-cell allorecognition and recognition by some mAbs.

Human cytotoxic T lymphocytes and activated peripheral blood lymphocytes enhance cytochalasin B-induced DNA fragmentation of indicator bystander cells

The cytochalasins are known to have multiple effects on cellular function. Not only do they induce secretion from granule compartments but they can induce DNA fragmentation in numerous cells. Evidence is presented which shows that treatment of human cytotoxic T lymphocytes and activated peripheral blood lymphocytes with cytochalasin B induces release of a factor capable of enhancing DNA fragmentation in cytochalasin-susceptible target cells. This activity can be transferred in the supernatants of cytochalasin B-activated CTL.