Biomedical subjects

R N Germain

Publications and source records attributed to R N Germain.

At least 127 records · Page 7Linked to original sources

PubMed1988

Processing of a minimal antigenic peptide alters its interaction with MHC molecules.

Before their recognition by T lymphocytes, protein antigens generally require processing by antigen-presenting cells. In a poorly understood series of events, the protein antigen is internalized, transformed and re-expressed on the surface of the antigen-presenting cell in association with gene products of the major histocompatibility complex (MHC). Small peptides derived from the native protein can be recognized in the absence of antigen processing, suggesting that processing involves proteolytic degradation. These peptides are thought to mimic the naturally produced peptide fragment. We describe here a synthetic peptide antigen of this type which does not require processing but which is nevertheless further processed by splenic antigen-presenting cells. Interestingly, this processing event specifically alters the interaction of the peptide with the class II MHC (Ia) molecule, markedly affecting both its potency as an antigen in vitro and its immunogenicity in vivo (IR gene control).

Animals↗

PubMed1988

Activation properties of T cell receptor-gamma delta hybridomas expressing diversity in both gamma- and delta-chains.

To elucidate the structure, diversity, and activation properties of the murine T3-associated gamma delta-receptor, examination was made of the gamma delta and T3 components, T cell receptor (TCR) gene transcription, activation properties, and lymphokine production in a panel of four cloned T cell hybridomas expressing a TCR-gamma delta. Biochemical analysis of the gamma and delta proteins expressed on these hybridomas reveals new gamma and delta species not observed in whole populations of dLy-1 Lyt-2-L3T4-thymocytes from which these hybridomas were derived. Thus, analysis of expression of the TCR-gamma delta complex at the clonal level indicates that both gamma and delta appear to be expressed as multiple distinct gene products within a homozygous inbred mouse strain. Northern blot analysis reveals that, whereas all gamma delta hybridomas had mature 1.5-kb TCR-alpha-chain and mature TCR-gamma-chain transcripts, none had mature 1.3-kb TCR-beta-chain transcripts, thus indicating that the type of TCR heterodimer expressed reflects of the state of TCR gene transcription in these hybridomas. Our results also reveal striking similarities between TCR-gamma delta and TCR-alpha beta cells with respect to their activation properties. First, all five of the T3 components associated with the gamma delta-complex are of the same size and have the same glycosylation patterns as those associated with alpha beta-heterodimers. Second, induction of function in these gamma delta cells (assayed by lymphokine production) can be achieved with a variety of stimuli known to elicit activation signals in alpha beta cells as well: direct receptor-engagement (i.e., through anti-Thy-1), and phorbol 12-myristate 13-acetate-plus-ionomycin-mediated. Collectively, these findings suggest that gamma delta T cells express a receptor of at least limited diversity and use T3-mediated activation pathways very similar to those employed by TCR-alpha beta-bearing T cells.

Animals↗

PubMed1988

Mitogenic activation of EL-4 cells does not require surface Thy-1 expression.

The ability of monoclonal anti-Thy-1 antibodies to stimulate IL-2 production and T-cell proliferation has raised the possibility that Thy-1 may play an important role in T-cell activation. To examine this postulated role we have produced Thy-1-negative variants of the murine T lymphoma EL-4 by mutagenesis with ethyl methanesulfonate (EMS) and subsequent negative selection with anti-Thy-1 monoclonal antibodies (mAbs) and complement. Although the parental EL-4 cell line produced interleukin-2 (IL-2) in response to concanavalin A (Con A), phytohemagglutinin, anti-Thy-1 mAbs, and an anti-T3 mAb, as well as after exposure to phorbol myristate acetate (PMA), only PMA was capable of inducing IL-2 production by several Thy-1-negative cell lines. The loss of responsiveness to cell surface stimulatory ligands appeared to be correlated with loss of Thy-1 expression because mutagenized cells selected for high levels of Thy-1 expression all responded normally to Con A. However, when Thy-1 expression was reconstituted in the "nonresponder" (Thy-1-negative) cell lines either by transfection of a Thy-1.2 gene or by 5-azadeoxycytidine treatment, the revertant cell lines were still unable to produce IL-2 when stimulated with Con A, anti-Thy-1, or anti-T3. Furthermore, several other independently derived Thy-1-negative EL-4 cell lines responded normally to mitogens and mitogenic mAbs. Taken together, these results suggest that Thy-1 expression is not required for the T-cell activation process and that the EMS mutagenesis procedure resulted in an additional mutation(s) responsible for the inability of certain Thy-1-negative cell lines to be triggered by mitogens and mitogenic mAbs. These cell lines may prove to be valuable tools for further biochemical and molecular studies of the sequence of events associated with T-cell activation.

Animals↗

PubMed1988

An immunodominant epitope of the human immunodeficiency virus envelope glycoprotein gp160 recognized by class I major histocompatibility complex molecule-restricted murine cytotoxic T lymphocytes.

Because cytotoxic T lymphocytes (CTL) may be important for preventing direct cell-to-cell transmission of human immunodeficiency virus (HIV), the agent responsible for acquired immunodeficiency syndrome, we have begun to investigate the epitope specificity and immune response (Ir) gene control of anti-HIV CTL responses in experimental animals. Mice were infected with a recombinant vaccinia virus expressing the HIV gp160 envelope gene, and the primed lymphocytes were restimulated in vitro with a transfected histocompatible cell line expressing the same gene. Our results show that H-2d mice are CTL high responders and H-2k mice are low responders to the HIV gp160 envelope protein under these conditions. Moreover, the H-2d mice respond predominantly to a single immunodominant site represented by a 15-residue synthetic peptide conforming to the amphipathic alpha-helix model of T-cell epitopes and seen by CD4- CD8+ CTL in association with the Dd class I major histocompatibility complex (MHC) molecules. The facts that CTL responses were detected in the context of only one of four class I MHC molecules tested and that the response was limited predominantly to a single epitope indicate that the CTL repertoire elicited by the HIV envelope protein in association with murine class I MHC molecules may be very limited. In addition, this epitope occurs in a highly variable segment of the envelope protein. This puts constraints on the use of a single peptide sequence from this region in a vaccine, as such a vaccine would have to be polyvalent. Nevertheless, this same variability suggests that this region may be under selective pressure from human CTL, and therefore that this site may be immunodominant in humans as well as mice and so of clinical importance in vaccine development.

Acquired Immunodeficiency Syndrome↗

PubMed1988

The generation and selection of the T cell repertoire: insights from studies of the molecular basis of T cell recognition.

The molecular basis of T cell corecognition of antigen and products of the major histocompatibility complex (MHC) was examined using the technique of DNA-mediated gene transfer. Introduction of the genes encoding the alpha and beta chains of the clonotypic molecule (Ti) of the pigeon cytochrome c-specific, I-Ek-restricted murine T cell hybridoma 2B4 into the human leukemic T cell Jurkat or its T3- variants led to the surface expression of various dimeric combinations of human and mouse Ti chains. All alpha beta dimers were associated in a 1:1 ratio with the chains of the T3 complex and all Ti-T3 complexes could transmit effective transmembrane signals for IL2 gene activation following binding and cross-linking by anti-T3 or anti-clonotypic antibodies. However, only the reconstituted mouse 2B4 alpha beta dimer mediated functional responses to antigen-presenting cells bearing the appropriate combination of antigen and Ia molecules. The fine specificity of the antigen-MHC molecule responses precisely matched that of the 2B4 T cell gene donor, establishing that the alpha beta clonotypic molecule is both necessary and sufficient to fully define the dual specificity of a T cell. This result, together with similar data from other laboratories, provides direct evidence in favor of the "single receptor" model of T cell recognition. Analysis of past experiments looking for independent recognition of antigen vs. MHC molecules led us to conclude that limitations on either formation of mixed receptor dimers or of appropriate antigen peptide-Ia molecule pairs may have limited the utility of these studies in providing an answer to this question. Therefore, additional gene transfer experiments were carried out to investigate the role of the two chains of the alpha beta heterodimer in controlling antigen vs. MHC molecule specificity. Our results showed that under conditions in which it was assured that antigen-Ia complexes formed, one could produce a receptor molecule composed of the alpha chain of one T cell hybridoma (2H10) and the beta chain of a second hybridoma (2B4) with a mixed antigen and MHC molecule specificity that could be predicted based on the specificities of the parent T cells. We discuss at length the implication of this result for the issue of single- vs. dual-site recognition models of T cell receptor function. In addition to these results looking directly at specificity of receptor molecules, we have also analyzed expression of various combinations of Ti chains. For alpha and beta, clear asymmetries in the efficiency of surface receptor expression were observed for certain pairs of chains.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

The molecular basis of MHC-restricted antigen recognition by T cells.

In order to determine the contribution of the clonotypic T cell receptor (Ti) alpha beta heterodimer to the antigen/MHC specificity of mature T cells, we have transfected cloned Ti alpha and/or beta genes into either human or mouse T cells, and analyzed the transfectants for Ti-T3 expression and responses to antigen and Ia molecules. Our analysis establishes that a single receptor structure (the Ti alpha beta heterodimer) is necessary and sufficient to define the dual specificity of T cell antigen recognition and suggests that in at least certain instances Ti beta chains play a predominant role in MHC restriction specificity, raising the possibility of a "one receptor, two sites" model of T cell recognition.

Animals↗

PubMed1988

The molecular basis of antigen presentation.

We have used a multifactorial approach to investigate the relationship between the structure of class II major histocompatibility complex (MHC)-encoded cell surface molecules (Ia) and the recognition of Ia-bound peptide antigens by clonally distributed alpha beta heterodimeric T cell receptors (TCR). Four distinct parameters of Ia structure-function--1) control of Ia assembly and transport to the surface membrane; 2) serological reactivity with panels of monoclonal antibodies; 3) ability to present peptide antigens to T cells for functional activation; and 4) differential peptide binding independent of the TCR--have been measured. This has allowed assignment of allelically polymorphic subregions or individual residues to locations in a model class II molecular structure and attribution to these subregions and residues of specific functions such as control of alpha beta chain interaction and protein folding, antigenic peptide binding, or TCR binding. The results of these analyses have provided an internally consistent picture of the class II molecule that fits well with a hypothetical model for Ia derived by analogy from the recently solved HLA class I crystal structure. They have also given us the first clear definition of specific peptide binding residues within the general peptide binding region of Ia and have revealed an unexpected asymmetry in the structure-function relationships of the putative alpha and beta chain helical regions. Overall, the results of these studies indicate the critical importance of multi-parameter analysis in creating useful molecular models using non-chemical techniques. They also suggest that hypotheses about TCR-Ia interaction may have to take into account a significant asymmetry in the function of the two major polymorphic regions of histocompatibility molecules.

Animals↗

PubMed1987

Cell surface T3 expression requires the presence of both alpha- and beta-chains of the T cell receptor.

We have identified a surface T3- Jurkat variant which has a defective alpha-chain but which possesses an intact beta-chain. The transfection of a functional mouse alpha-chain into this human T cell induces the expression of surface T3 molecules associated with mouse alpha-human beta-heterodimers detected by anticlonotypic antibodies. Treatment of the transfectant with anti-T3, anti-mouse Ti-alpha, or anti-human Ti-beta antibodies clears all Ti-T3 complexes from the surface. These results demonstrate that functional alpha- and beta-chains are both required for expression of T3 on the cell membrane, and that the Ti heterodimers present and associated with T3 on Jurkat cells involve only alpha- and beta-chains.

Antibodies, Monoclonal↗

PubMed1987

Structure-function analysis of the Abm12 beta mutation using site-directed mutagenesis and DNA-mediated gene transfer.

The B6.C-H-2bm12 (bm12) mouse possesses a naturally occurring mutation in its class II MHC A beta gene. The three amino acid substitutions at positions 67, 70, and 71 that comprise this mutation lead to changes in both Ia expression and immune recognition of the resultant A beta A alpha molecule. The experiments reported here utilize a combination of oligonucleotide-mediated site-directed mutagenesis and DNA-mediated gene transfer to explore the roles played by each of the three mutant residues in these various phenotypic changes. A beta genes comprising all permutations of the residues distinguishing Ab beta from Abm12 beta were created and were individually co-transfected with Ab beta into mouse L cells. Sublines expressing high levels of membrane Ia were selected by preparative flow cytometry and were studied for reactivity with a panel of monoclonal anti-Ia antibodies, or for their ability to act as antigen-presenting cells (APC) for the stimulation of T cell hybridomas. During the generation of these transfectant lines, it was noted that expression of a high level of Abm12 beta Ab alpha was more difficult to achieve than a similar level of Ab beta Ab alpha. Northern blot analysis of specific A beta and A alpha mRNA levels in these various lines indicated that more class II mRNA, and presumably more A beta and A alpha chains, were required to achieve expression of Abm12 beta Ab alpha equal to that of Ab beta Ab alpha, suggesting that the previously noted reduction of Ia expression on cells from bm12 mice reflects a decreased ability of Abm12 beta Ab alpha chains to pair, or to reach the membrane. Staining of the panel of transfectants with monoclonal antibodies revealed that antibodies which did not distinguish Ab beta Ab alpha from Abm12 beta Ab alpha also reacted equally well with all molecules involving in vitro mutant A beta chains. Monoclonal antibodies reactive with Ab beta Ab alpha but not Abm12 beta Ab alpha were specific for an epitope primarily determined by the presence or absence of Arg 70 in Ab beta. In striking contrast, all three mutant positions were found to play crucial roles in T cell recognition, because all substitutions led to significant or complete loss of antigen-presenting function with all but one of the T hybridomas tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

PubMed1987

Induction of macrophage Ia antigen expression by rIFN-gamma and down-regulation by IFN-alpha/beta and dexamethasone are mediated by changes in steady-state levels of Ia mRNA.

In previous studies, the induction of Ia antigens on murine peritoneal exudate macrophages by recombinant IFN-gamma (rIFN-gamma) and the antagonism of rIFN-gamma-induced Ia expression by the inhibitors IFN-alpha/beta and glucocorticoids have been examined. In this report, these findings have been extended to an analysis of total or cytoplasmic mRNA from macrophage cultures treated with rIFN-gamma in the absence or presence of these two inhibitors. Recombinant IFN-gamma induced a 5.7- to 6.5-fold increase in steady-state levels of Ia (A alpha-specific) mRNA. Coordinate increases in steady-state mRNA for A beta, and E alpha were observed in response to rIFN-gamma. Maximum induction occurred 24 hr post-treatment and required the continued presence of rIFN-gamma. Induction of A alpha-specific mRNA was sensitive to the protein synthesis inhibitor cycloheximide. Simultaneous treatment of macrophage cultures with rIFN-gamma and IFN-alpha/beta or the glucocorticoid dexamethasone (DEX) resulted in a significant decrease in steady-state, A alpha-specific mRNA levels compared with treatment with rIFN-gamma alone. This analysis suggests that both the induction of Ia expression by rIFN-gamma, and the antagonism of rIFN-gamma-induced Ia gene expression by IFN-alpha/beta and DEX, are regulated by cognate changes in Ia mRNA.

Animals↗

PubMed1987

Early genetic events in T cell development analyzed by in situ hybridization.

In situ hybridization was used to investigate the expression of T cell receptor (TCR) alpha, beta, and gamma mRNAs in developing fetal and adult precursor thymocytes. gamma transcription was observed at the earliest time tested (day 12), followed by beta 12 h later, and TCR alpha on day 16. The early beta transcripts appeared to be from unrearranged or incompletely rearranged (D-J-C) beta loci. V beta region transcription was first detectable on day 14 and transcription of different V beta genes was induced at different times. These results delineate a schedule sequence of TCR gene activation, which begins within 1 d after entry of stem cells into the fetal thymus.

Animals↗

PubMed1987

Predominant role of amino-terminal sequences in dictating efficiency of class II major histocompatibility complex alpha beta dimer expression.

Cell surface expression of class II major histocompatibility complex-encoded (Ia) molecules depends on association of the component alpha and beta chains into a stable heterodimer. In the mouse, two isotypes of class II molecules have been identified, A beta A alpha and E beta E alpha. However, experiments from this laboratory have shown that, following DNA-mediated gene transfer into murine L cells, an A beta E alpha-mixed-isotype molecule can be assembled and expressed at the cell surface. In the present study, we have investigated the structural features of the beta chain that control the extent of association and level of membrane expression of A beta E alpha interisotypic pairs. The use of intact allelic A beta genes demonstrated that only A beta d chains, but not A beta b or A beta k chains, can be coexpressed on the surface membrane with E alpha chains. Transfection of recombinant A beta genes that encode all or half of the beta 1 domain from one allele and the rest of the chain from another allele revealed that the 5-7 polymorphic residues in the amino-terminal 50 residues of the A beta chain completely controlled this variation in expression with E alpha. Isotypically mixed beta genes encoding the A beta 1 domain of either A beta d or A beta k chains and the beta 2, transmembrane, and intracytoplasmic portions of E beta chains were used to assess the role of isotypically conserved structures in alpha beta pairing and expression. In marked contrast to the major alterations in expression accompanying changes in the amino-terminal polymorphic residues, exchange of these carboxyl-terminal isotypic segments had no detectable influence on the efficiency of expression with either A alpha or E alpha chains. These results argue strongly that variations in the efficiency with which distinct Ia alpha beta dimers assemble and are transported to the membrane is determined almost exclusively by a critical chain interaction involving the amino-terminal domains of the molecules.

Alleles↗

PubMed1987

Thy-1+ dendritic epidermal cells belong to the T-cell lineage.

The murine epidermis contains a population of dendritic, Thy-1+ cells (Thy-1+ DEC). Although it is now clear that these cells are of bone marrow origin, extensive morphological, histochemical, and cell-membrane marker studies have not definitively placed them in any known hematopoietic differentiation pathway. Based on the observation that Thy-1+ DEC can be propagated in vitro with Con A and interleukin 2, we have established three cell lines (Tehy 184, Tehy 245, and Yety 245) that can be continuously grown in medium with lectin-lymphokine-rich culture supernatants of rat spleen cells. With the exception of the loss of reactivity with anti-asialo-GM1 antibodies (Tehy 184 and Tehy 245) and the gain of interleukin 2 receptor expression, the cultured cell lines bear the same surface characteristics as freshly isolated Thy-1+ DEC: Thy-1+, Ly-5+, Lyt-1-, Lyt-2-, L3T4-, Ia-, sIg-. Using Southern and RNA gel blot analysis, we now demonstrate that these Thy-1+ DEC-derived cell lines exhibit various patterns of rearrangements in the gene complexes encoding the T-cell receptor (related) beta and gamma chains and contain mature and/or incomplete transcripts from the T-cell receptor alpha- and beta-chain genes, as well as transcripts from the receptor-related gamma-chain genes. Tehy 184 cells, the only cells containing both mature alpha- and beta-chain transcripts, react positively with the F23.1 monoclonal antibody, which recognizes the product of a subset of T-cell receptor beta-chain variable region gene segments. This antibody precipitates a surface protein of 84-88 kDa from these cells that after reduction separates into two 40- to 44-kDa chains, characteristic of Ti alpha/beta heterodimers. These data strongly suggest that Thy-1+ DEC belong to the T-cell lineage and point to the epidermis as a site either of immature thymocyte migration or of extrathymic T-cell differentiation.

Animals↗

PubMed1987

Allele-specific control of Ia molecule surface expression and conformation: implications for a general model of Ia structure-function relationships.

Sequence polymorphism of class II major histocompatibility complex-encoded molecules (Ia) not only accounts for the allelic variability in Ia structure relevant to T-lymphocyte responses but also seems to result in differential quantitative expression of particular Ia heterodimers. The contributions of different allelically variable regions of Ia molecules to both of these processes were analyzed by transfection of L cells with various A beta and A alpha gene pairs. The results show that, with regard to quantitative and qualitative aspects of Ia expression, the polymorphisms in the A beta chain segregate into two groups. Those in the NH2-terminal half of A beta 1 have a consistent role in controlling beta-alpha chain interactions, efficiency of dimer expression, and Ia conformation and probably are in the interior of the Ia molecule at the site of beta-alpha domain interaction. Polymorphisms in the COOH-terminal half of A beta 1 contribute to those structures that directly interact with antibodies, antigen, and/or T-cell receptors, consistent with their presence on the surface of the Ia heterodimer. This analysis provides a model for understanding both overall class II molecular structure and the relationship between this structure and immune recognition. It also suggests an explanation for the evolution of certain features of class II genes.

Alleles↗

PubMed1986

Characterization of T cell receptor gamma chain expression in a subset of murine thymocytes.

While much information exists about the structure and function of the clonally distributed T cell receptor (TCR) alpha beta heterodimer, little is known about the gamma protein, the product of a third rearranging TCR gene. An antiserum to a carboxyl-terminal peptide common to several of the murine gamma chain constant regions and a monoclonal antibody to the murine T3 complex were used to identify products of this TCR gene family in a subpopulation of Lyt2-, L3T4- thymocytes. This subpopulation does not express TCR alpha or full-length TCR beta messenger RNA. The gamma chain is a 35-kilodalton (kD) protein that is disulfide-bonded to a 45-kD partner and is associated with the T3 complex. Analysis of the glycosylation pattern of this thymic gamma chain revealed that the major variable region gamma (V gamma) gene transcribed in activated peripheral T cells is absent from this subpopulation. The cells that bear this second T cell receptor may therefore represent a distinct lineage differentiating within the thymus.

Amino Acid Sequence↗

PubMed1986

Efficient cell surface expression of class II MHC molecules in the absence of associated invariant chain.

The intracytoplasmic forms of class II (or Ia) major histocompatibility complex heterodimers are associated with a third glycoprotein, termed the invariant chain (Ii). This specific interaction has led to the view that Ii plays a necessary role in the assembly, intracellular transport, and/or membrane insertion of Ia molecules. To test this hypothesis directly, we have transfected complementary DNA clones that encode murine class II alpha and beta chains into cells that do not express any endogenous Ii messenger RNA (mRNA) (COS-7 and BALB/c 3T3 cells). After DNA-mediated gene transfer, significant cell surface expression of Ia was observed in transient expression assays using COS-7 cells and a stable expression system using BALB/c 3T3 cells. Furthermore, the total levels of class II alpha and beta mRNA were similar in Ii- cells (transfected BALB/c 3T3) and in Ii+ cells (B cell hybridoma) that expressed nearly identical amounts of surface Ia, suggesting that the efficiency of Ia expression was equivalent in the two cell types and, therefore, independent of Ii. These results indicate that the physiologic role for Ii is not simply to mediate membrane expression of Ia molecules, and that alternative hypotheses concerning the true function of this molecule need to be considered.

Antigens, Differentiation, B-Lymphocyte↗

PubMed1986

Transfected human B lymphoblastoid cells express the mouse Ad beta-chain in association with DR alpha.

The human EBV-transformed cell line TOM was transfected with plasmid DNA containing a complete genomic copy of the murine class II Ad beta gene. Drug resistant transfectant clones showed cell surface expression of the Ad beta gene product, as detected by flow microfluorimetry when using a mouse monoclonal antibody (MKD6) specific for Ad beta. Immunoprecipitation and two-dimensional gel electrophoretic analysis of the Ad beta-containing molecules from the transfected cells revealed that the mouse beta-chain was expressed in noncovalent association with the human DR alpha-chain rather than with DQ alpha, the human A alpha homologue. The implications of this unexpected pairing for our understanding of the processes controlling the association of class II alpha and beta gene products and of the roles of Ia molecules in normal and pathologic immune function are discussed.

Animals↗

PubMed1986

I-A-restricted T cell antigen recognition. Analysis of the roles of A alpha and A beta using DNA-mediated gene transfer.

The contributions of A alpha and A beta chains, and of subregions of A beta, to Ia-restricted recognition of antigen by Th lymphocytes were analyzed using a panel of L cells transfected with various pairs of A alpha b,d, or k genes and recombinant or wild-type A beta b,d, or k genes. The A beta genes included all possible exchanges of the whole NH2-terminal (beta 1) domain or halves of the beta 1 domain among these three allelic A beta genes. The Ia+ L cells derived from such transfections were used as antigen-presenting cells with a 21 member panel of responding Ia-restricted T hybridoma cells of differing nominal antigen specificity and Ia-restriction. Special care was taken to account for quantitative variation in levels of Ia expression throughout the experiments. The results of this analysis reveal that (a) only 2 of the 21 Th cells recognized Ia molecules involving either a nonparental A alpha or a nonparental A beta chain, and in both cases the degeneracy extended to only one of the two other alleles tested. This suggests that allele specific contributions from both A alpha and A beta chains are important in restricted recognition for most, if not all I-A-restricted Th cells. (b) In no case did substitution of the A beta 2 domain from either of the alternative haplotypes lead to any functionally detectable effects, demonstrating that polymorphisms in the A beta 1 domain can entirely account for the restriction imposed on Th cell responses by the entire A beta chain. (c) For 90% of the cells tested, replacement of the NH2-terminal portion of the beta 1 domain with an allogeneic segment led to Ia molecules unable to elicit Th responses. Furthermore, of all the cells permissive of the substitution of one or other half of the beta 1 domain, only two permitted the substitution of sequence from both alternative haplotypes. Taken together, these data strongly suggest that antigen recognition by most, if not all, I-A-restricted Th cells involves contributions from both halves of the A beta 1 domain. These data suggest that the role of I-A molecules in restricted Th cell recognition of antigen depends on conformational determinants unique to a particular combination of polymorphic alpha and beta chains, and that multiple such sites exist on a single Ia molecule.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗