The role of polymorphic I-Ak beta chain residues in presentation of a peptide from myelin basic protein.

Allelic differences in major histocompatibility complex (MHC)-encoded class II molecules affect both the binding of immunogenic peptides to class II molecules and the recognition ofMHC molecule-peptide complexes by T cells. As yet, there has been no extensive mapping of these functions to the rme structure of human class II molecules. To determine sites on the HLA-DR3 molecule involved in antigen presentation to T cells, we used monoclonal antibodies specific for HLA-DR3 to immunoselect mutants of a B-lymphoblastoid line. We located the sites of single amino acid substitutions in the HLA-DR3 molecule and correlated these structural changes with patterns of recognition by HLA-DR3-restricted, antigenspecific T cells, allospecific T cells, and allospecific anti-DR3 monoclonal antibodies. We analyzed seven mutations. One mutation, at position 74 in domain 1 of the DR j3 chain, affected recognition by all T cells tested, whereas others, at positions 9, 45, 73, 151, and 204 of the DR P chain and position 115 of the DR a chain, altered recognition by some T cells, but not others. Each of the substitutions resulted in a unique pattern of T-cell stimulation. In addition, each T-cell clone recognized a different subset of the mutants. These results indicate that different residues of the DR3 molecule are involved in presentation of antigen to different DR3-restricted T cells. These studies further show that substitutions which most likely affect peptide binding alter recognition of DR3 molecules by an alloreactive T-cell clone and some allospeciflic antibodies.Major histocompatibility complex (MHC) molecules are highly polymorphic cell surface glycoproteins whose most evident and best understood function is to present immunogenic peptide antigens to T lymphocytes (1, 2). In addition, allelic variation in MHC class II molecules is associated with susceptibility or resistance to autoimmune diseases (3). The essential relationship between the polymorphism of MHC molecules and their function is well documented (4) and suggests that the locations of the hypervariable regions of MHC class II molecules are likely to identify functional domains (5, 6). However, only a few studies have examined the particular contribution of individual class II residues to antigen presentation, in murine (7-9) or human (10) systems.Brown et al. (11) have proposed a structural model of the class II binding domain for antigen, based on the crystal structure of an MHC class I molecule. This model identifies amino acid residues that are involved in peptide binding or in T-cell interactions based on their locations and the orientation of their side chains. One experimental approach for determining the function of individual amino acid residues, and thus testing the model's predictions, is to generate somatic cell mutants with single amino acid substitutions in class II molecules, to map their mutations, and to characterize their functional defects. Using a B-lymphoblastoid cell line (B-LCL) as progenitor, we have immunoselected mutants with sin...

Section: Discussionmentioning

confidence: 88%

mentioning

confidence: 99%

Point mutations define positions in HLA-DR3 molecules that affect antigen presentation.

Mellins

Arp

Singh

et al. 1990

“…Thus, it has been possible to develop successful immunotherapy of experimental autoimmune encephalitis (3,4) and type II collagen and collagen-induced arthritis. In many of these models, administration of the immunodominant epitope of, for example, myelin basic protein, has been successful in preventing or stopping the progression of neurological symptoms in animals already developing the illness, even after immunization with whole spinal cord emulsified in CFA.…”

Section: Studies In Animal Modelsmentioning

confidence: 99%

“…For the most part, these strategies have attempted to address autoimmune diseases in which the primary pathogenic mechanism and the principal effector mechanism seem to be the result of activated T cells inducing inflammation and damage in a variety of tissues (2). Much of this experimentation has dealt with experimental models of multiple sclerosis (MS) (experimental autoimmune encephalitis) (3,4), rheumatoid arthritis (for which one experimental model is type 2 collagen-induced arthritis), and type 1 diabetes (T1DM) (5), in which the spontaneous disease in nonobese diabetic (NOD) mice is the primary model. Although in antibody-mediated diseases the target of the autoantibodies is frequently well defined, less effort has been directed toward developing specific antigen vaccination to treat the T cells activating these diseases.…”

mentioning

confidence: 99%

Specific antigen vaccination to treat autoimmune disease

McDevitt

2004

Specific antigen vaccination by administration of the target antigen in aqueous solution has resulted in significant decreases of disease severity in animal models of experimental allergic encephalomyelitis, type I diabetes, and several forms of antigen-induced arthritis, even if administered after the initiation of symptoms. However, in experimental autoimmune encephalomyelitis (EAE) and type I diabetes in nonobese diabetic (NOD) mice, repeated administration of peptide fragments of target antigens in incomplete Freund's adjuvant has resulted in severe anaphylactic reactions. Although these methods of administration are known to potentiate CD4 T helper 2 (Th2) responses, which is the goal of specific antigen vaccination, the risk of anaphylaxis raises a red flag concerning use of this therapy for diseases such as type I diabetes, where the survival time after onset is quite long. It is clear that specific antigen vaccination is effective in preventing several animal models of autoimmune disease, and in treating these diseases once the symptoms are overt. However, the risks of this therapy require serious consideration of alternative methods for down-regulation of the autoimmune process.

“…Exceptions are nifA itself and the reiteratedfix region (10,11). Recent evidence has suggested that in R. meliloti, nifA transcription is controlled primarily by oxygen availability (11).…”

mentioning

confidence: 99%

Common regulatory elements control symbiotic and microaerobic induction of nifA in Rhizobium meliloti.

Virts¹,

Stanfield²,

Helinski³

et al. 1988

We have previously demonstrated that the nifA promoter (nifAp) of Rhizobium melioti is inducible under microaerobic conditions in the absence of alfalfa. Here we show that microaerobic activation of nifAp involves both cisand trans-acting regulatory controls identical to those used symbiotically. The start site for nifA mRNA synthesis was found to be the same during symbiosis and microaerobiosis, and a deletion analysis of nifAp demonstrated that DNA between positions -62 and -45 is essential for induction. Mutants isolated as being unable to induce nifA microaerobically also were found to be defective in symbiotic nitrogen fixation with alfalfa. Such mutants form nodules that are equivalent cytologically to those induced by nifA::TnS mutants. Genetic and structural studies have localized the mutations to a cluster of fix genes 200 kilobases distant from the nod-nif region on the pSym megaplasmid [Renalier,