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J K Russell

Publications and source records attributed to J K Russell.

At least 19 recordsLinked to original sources
PubMed1992

Evidence for the alpha-helicity of class II MHC molecular binding sites for the superantigen, staphylococcal enterotoxin A.

Circular dichroism (CD) spectra of class II MHC peptides revealed the alpha-helical conformation of superantigen-binding peptides I-A beta b(60-90), I-A beta b(65-85), and I-A alpha b(51-80), but not the nonbinding peptide I-A beta b(80-100). These CD spectra provide biophysical evidence for the alpha-helicity of class II MHC molecular binding sites for the superantigen, staphylococcal enterotoxin A (SEA). Alanine-substituted analogs of the SEA binding-site peptide, I-A beta b(65-85), were used to implicate beta-chain residues 72 and 80 in class II MHC-SEA binding. The data support SEA binding away from the class II antigen binding cleft along the faces of the alpha-helices.

Amino Acid Sequence↗
PubMed1991

Both alpha-helices along the major histocompatibility complex binding cleft are required for staphylococcal enterotoxin A function.

The superantigen staphylococcal enterotoxin A (SEA) requires interaction with class II major histocompatibility complex (MHC) molecules to activate T cells. We have previously used the synthetic peptide approach to establish one side of the hypothetical class II foreign-antigen binding cleft, alpha-helical region 65-85 of the beta chain, as a binding site involved in accessory cell presentation of SEA to T cells. To further characterize the structural basis for MHC-SEA interaction we have examined the role of the alpha-helical regions of the class II alpha and beta chains in SEA function. Using the synthetic peptide approach, we have found that both alpha-helical regions are required for SEA-induced proliferation. Their corresponding peptides directly bound SEA. Although the beta-chain peptides were able to inhibit SEA binding to human and mouse cells, the alpha-chain peptides were not. The data suggest that the alpha-helices along both sides of the hypothetical class II MHC molecule binding cleft are required for SEA-induced function, whereas the beta-chain alpha-helix is sufficient for SEA binding. A model of superantigen presentation is proposed wherein the MHC beta chain, possibly region 70-80, interacts with SEA region 1-45, whereas another region of SEA binds region 51-80 of the alpha chain.

Binding Sites↗
PubMed1991

Structural basis for differential binding of staphylococcal enterotoxin A and toxic shock syndrome toxin 1 to class II major histocompatibility molecules.

The related staphylococcal toxins staphylococcal enterotoxin A (SEA) and toxic shock syndrome toxin 1 (TSST-1) are microbial superantigens. They require interaction with class II major histocompatibility complex (MHC) molecules to activate T cells. We have previously identified a binding site on SEA, the N-terminal 45 amino acids, as well as its corresponding receptor on the MHC antigen, residues 65-85 of the beta chain. To further characterize the structural basis for SEA binding to class II MHC molecules we have examined its relationship to TSST-1 binding. Both toxins bound similarly to murine A20 cells, but blockage of binding was observed only with the homologous toxin, which suggests that the binding sites for the two toxins on A20 cells are distinct. In contrast, specific binding of SEA was greater than that of TSST-1 on human Raji cells. Further, SEA was a better inhibitor of TSST-1 binding than was TSST-1 itself at low concentrations, but TSST-1 only minimally inhibited SEA binding. The data suggest that TSST-1 interacts with Raji cells at an SEA binding site, but with a lower affinity. The peptides SEA-(1-45) and I-A beta b-(65-85) were capable of blocking SEA binding on both A20 and Raji cells, but blockage was more effective on A20 cells. Neither peptide was capable of blocking TSST-1 binding on either cell line. The data are compatible with a model in which SEA has a binding site on A20 cells involving SEA-(1-45) and I-A beta b-(65-85) which is distinct from that which binds TSST-1, while at least two binding sites are present on Raji cells. One site involves predominantly the residue 1-45 region on SEA and the 65-85 region of the MHC beta chain, while the other site involves both a different region on the SEA molecule and a different site on the class II MHC molecule to which it binds. This latter site also binds TSST-1.

Animals↗
PubMed1991

Staphylococcal enterotoxin microbial superantigens.

Staphylococcal enterotoxins are a family of structurally related proteins that are produced by Staphylococcus aureus. In addition to their role in the pathogenicity of food poisoning, these microbial superantigens have profound effects on the immune system, which makes them useful tools for understanding its mechanism of action. These molecules (24-30 kDa) are highly hydrophilic and exhibit low alpha helix and high beta pleated sheet content, suggesting a flexible, accessible structure. Staphylococcal enterotoxins are among the most potent activators of T lymphocytes known. The receptors for staphylococcal enterotoxins on antigen-presenting cells are major histocompatibility complex (MHC) class II molecules. Further, the alpha-helical regions of the class II molecule are essential for function and appear to interact directly with the NH2-terminal region of staphylococcal enterotoxins such as SEA. Recent studies have shown that a complex of staphylococcal enterotoxin and MHC class II molecules is required for binding to the V beta region of the T cell antigen receptor. Staphylococcal enterotoxin mitogenic activity is dependent on induction of interleukin 2, which may be intimately involved in the mechanism of toxicity. The mouse minor lymphocyte stimulating (M1s) "endogenous" self-superantigen has been shown to be a retroviral gene product, so this too is apparently a microbial superantigen. An understanding of the mechanisms of action of these microbial superantigens has implications for normal and pathological immune functions.

Animals↗
PubMed1991

Staphylococcal enterotoxin superantigens.

Staphylococcal enterotoxins (SE) are a family of structurally related proteins that are produced by Staphylococcus aureus. They play a role in the pathogenesis of food poisoning and are the most potent activators of T lymphocytes known. The receptors for SE on antigen-presenting cells are major histocompatibility complex class II molecules. Recent studies have shown that a complex of SE and major histocompatibility complex class II molecules is required for binding to the variable region of the T cell antigen receptor beta-chain. SE mitogenic activity is dependent on induction of interleukin 2, which may be intimately involved in the mechanism of SE toxicity. The minor lymphocyte-stimulating "endogenous" self-superantigen has recently been shown to be a retroviral gene product, so that this too is apparently a microbial superantigen. An understanding of the mechanism of action of these microbial superantigens has implications for normal and pathological immune functions.

Animals↗
PubMed1990

The I-A beta b region (65-85) is a binding site for the superantigen, staphylococcal enterotoxin A.

Ia antigen is a receptor for the superantigen staphylococcal enterotoxin A (SEA). Peptides I-A beta b(30-60), I-A beta b(50-70), I-A beta b(65-85), and I-A beta b(80-100) of the MHC class II antigen beta chain on mouse (H-2b) accessory cells were synthesized. Only I-A beta b(65-85) inhibited SEA binding to the mouse B-cell lymphoma line, A20 (H-2d) and the human Burkitt's lymphoma line, Raji (HLA-DR). The I-A beta b(65-85) sequence is a predicted alpha-helix along the hypothetical antigen binding cleft of the Ia molecule. I-A beta b(65-85) also directly and specifically bound both the intact SEA molecule and its Ia binding site, represented by the peptide SEA(1-45). The results suggest that I-A beta b region (65-85) is a necessary site for Ia molecular interaction with the superantigen SEA. Further, the data suggest that the same helical region of other Ia antigens binds SEA irrespective of haplotype and species.

Amino Acid Sequence↗
PubMed1990

Site of nonrestrictive binding of SEA to class II MHC antigens.

We have used the synthetic peptide approach to show that the N-terminal 45-amino acids of staphylococcal enterotoxin A (SEA), SEA(1-45), constitute an important part of its binding site on class II major histocompatibility complex (MHC) molecules. SEA(1-45) and to a lesser extent SEA(1-27) were able to displace SEA from HLA-DR on Raji cells as assessed by flow cytometry and to compete with radiolabeled SEA for interaction with HLA-DR in a direct binding assay. Specific binding of SEA to Ia on murine A-20 cells could be inhibited by the same peptides [i.e. SEA(1-45) greater than SEA(1-27)] that blocked binding to HLA-DR. Therefore, different class II MHC molecules associate with the same functional site on SEA. Further, an ELISA system was used to demonstrate that SEA(1-45) is able to directly bind to a mouse synthetic I-A beta b peptide, I-A beta b (65-85), which contains a binding site of the class II MHC molecule involved in SEA presentation to T cells. Thus, we have localized a site on SEA that is involved in selective surface association with class II MHC antigens and identified the region on the class II MHC antigen to which that site binds.

Animals↗
PubMed1989

Localization of an immune functional site on staphylococcal enterotoxin A using the synthetic peptide approach.

Using the synthetic peptide approach, we have identified a part of the staphylococcal enterotoxin A (SEA) molecule that is responsible for stimulation of T cell proliferation and induction of the lymphokine IFN-gamma. Peptides were synthesized corresponding to amino acids 1 to 27, SEA(1-27), and 28 to 45, SEA(28-45). Both peptides were tested for direct competition with SEA for blockage of SEA induced proliferation and production of IFN-gamma by T cells. Further, antibodies were produced to the peptides and tested for their ability to bind to SEA and block SEA function. SEA (1-27), but not SEA (28-45), blocked proliferation of human peripheral T cells and induction of IFN-gamma by the T cell line, L12-R4. The inhibitory effects were specific, because SEA (1-27) did not inhibit the induction of T cell proliferation by the mitogen PHA. Consistent with the direct inhibition of function, antibodies to SEA (1-27), but not SEA (28-45), neutralized the mitogenic activity of SEA on human PBL. The data suggest that a functional site on SEA that is responsible for its modulation of T cell function involves the N-terminal 27 amino acids. Residues 1 to 27 of SEA could potentially interact at either the level of the TCR or may block the proposed binding of SEA to class II MHC Ag, based on recent data showing that these molecules are involved in SEA-induced proliferation.

Amino Acid Sequence↗
PubMed1989

Causal association of interferon-gamma with tumor regression.

Mouse interferon-gamma (MuIFN-gamma) can cause the rejection of malignant cells in vivo. The evidence presented here in support of this claim includes, first, that spontaneous regression of MSC sarcomas was associated with high intratumoral concentrations of endogenously-produced MuIFN-gamma. By contrast, progressively growing, lethal neoplasms of the same kind invariably contained very little IFN-gamma. Second, spontaneously regressing MSC sarcomas were converted into progressively growing, lethal neoplasms by injecting mice with a monoclonal antibody that neutralized the biological effects of endogenous IFN-gamma. Another monoclonal antibody that bound to, but did not neutralize, mouse IFN-gamma had no effect on the course of tumor regression. Together, these data causally relate MuIFN-gamma to the successful rejection of malignant cells in vivo. They also suggest that findings of poor therapeutic efficacy for IFN-gamma are probably attributable to problems other than an intrinsic lack in the biological activity of the lymphokine.

Animals↗
PubMed1989

A positive feedback loop for staphylococcal enterotoxin-A-stimulated IFN-gamma production requires macrophage immune-associated antigen upregulation.

The C57Bl/6-derived T cell line, L12-R4, produced murine interferon-gamma (IFN gamma) in response to mitogenic stimulation by phorbol myristate acetate (PMA) or concanavalin A (Con A), but not by staphylococcal enterotoxin A (SEA). Low levels of IFN gamma were produced by SEA stimulation of L12-R4 cells cocultured with C57Bl/6 bone marrow macrophages (BMM). Significantly increased yields of IFN gamma resulted from 48-hour pretreatment of the BMM with recombinant IFN gamma (100 U/ml) prior to coculture. Polyclonal anti-IFN gamma and anti-IFN alpha/beta were used to characterize the interferon as IFN gamma. Paraformaldehyde (0.1%) treatment of IFN gamma-pretreated BMM did not affect IFN gamma production, suggesting that processing of SEA was not required. IFN gamma treatment of BMM resulted in significantly increased expression of immune-associated (Ia) antigen as determined by flow cytometric analysis, suggesting that the accessory cell role of BMM involved Ia antigen. Polyclonal anti-Ia antibody selectively inhibited the production of IFN gamma by SEA-stimulated whole spleen cell cultures, consistent with the necessity of Ia antigen for BMM help in SEA induction of IFN gamma. More interestingly, induction of IFN gamma. These findings suggest that Ia antigen is necessary for BMM accessory function in SEA induction of IFN gamma. More interestingly, the results implicate class II molecules in a positive feedback loop for IFN gamma production by SEA.

Animals↗
PubMed1988

Use of synthetic peptides to identify an N-terminal epitope on mouse gamma interferon that may be involved in function.

We previously have assigned N-terminal specificity to three hamster monoclonal antibodies (mAbs I, II, and III) produced to mouse recombinant gamma interferon (IFN-gamma), based on the ability of the N-terminal peptide IFN-gamma-(1-39) to block binding of 125I-labeled IFN-gamma (125I-IFN-gamma) and on the ability of these antibodies to bind 125I-IFN-gamma-(1-39). Only mAb I blocked function and binding to the IFN-gamma receptor, suggesting that it may bind to a region of the molecule involved in interaction with the receptor. To further define the epitope specificities of the antibodies, a series of N-terminal peptides were synthesized and tested for their ability to block antibody binding of 125I-IFN-gamma. Peptides IFN-gamma-(1-39), IFN-gamma-(1-20), IFN-gamma-(3-20), and IFN-gamma-(5-20) inhibited binding of 125I-IFN-gamma by mAb I in order of decreasing effectiveness, while peptide IFN-gamma-(7-20) was without effect. Peptides IFN-gamma-(1-39), IFN-gamma-(1-20), and IFN-gamma-(3-20) also inhibited binding of 125I-IFN-gamma by mAb II but were less effective when compared with their inhibition of mAb I. IFN-gamma-(5-20) and IFN-gamma-(7-20) did not inhibit binding by mAb II. Peptides IFN-gamma-(1-10), IFN-gamma-(10-30), and IFN-gamma-(21-44) did not inhibit either mAb I or mAb II. While IFN-gamma-(1-39) and IFN-gamma-(10-30) inhibited binding by mAb III, neither IFN-gamma-(1-20) nor any of its truncated forms were inhibitory. All three antibodies had similar Kd values for 125I-IFN-gamma. A prediction of the secondary structure of the molecule and the peptide inhibition data suggest that the epitope (possible receptor binding region) for mAb I involves a loop in the area containing residues 12-20, with sequences N-terminal to these residues possibly stabilizing the loop conformation. Direct evidence that the N-terminal 1-39 region of IFN-gamma is important in receptor binding was the observation that IFN-gamma-(1-39), but not the C-terminal IFN-gamma-(95-133), competed with 125I-IFN-gamma for the receptor on mouse L cells. IFN-gamma-(1-39) also specifically blocked IFN-gamma antiviral activity at concentrations that blocked binding to the receptor. The fact that IFN-gamma-(1-39) was the only peptide that blocked both IFN-gamma binding to receptor and function is consistent with the antibody competition data, where it was the most effective peptide in blocking binding of 125I-IFN-gamma by the N-terminal-specific mAbs. The combination of peptide mapping of epitope specificities and receptor competition should further help define the structural basis for IFN-gamma action.

Animals↗
PubMed1986

Epitope and functional specificity of monoclonal antibodies to mouse interferon-gamma: the synthetic peptide approach.

Spleen cells from hamsters immunized with recombinant mouse interferon-gamma (IFN-gamma) were fused with mouse myeloma cells, resulting in the production of four anti-IFN-gamma monoclonal antibodies. Binding of 125I-IFN-gamma by these protein A-bound antibodies was specifically blocked by cold IFN-gamma. Binding by three of these antibodies was also blocked by a synthetic peptide corresponding to the N-terminal 1-39 amino acids of IFN-gamma, whereas a corresponding C-terminal (95-133) peptide had no effect on binding. The N-terminal specificity of these three antibodies was confirmed by their specific binding of 125I-N-terminal (1-39) peptide. One of the N-terminal specific monoclonal antibodies inhibited both antiviral and macrophage priming (for tumor cell killing) activities of IFN-gamma, whereas the other two had no effect on either biologic function. The selectivity of the inhibition of IFN-gamma function was not due to a differential ability of the N-terminal specific antibodies to bind IFN-gamma. Blocking experiments with cold IFN-gamma and N-terminal peptide suggest that the epitope specificities of the monoclonal antibodies could be determined by the conformational or topographic structure of IFN-gamma. An exact determination of the epitope specificity of the monoclonal antibody that inhibited IFN-gamma function could provide insight into the structural basis for the role of the N-terminal domain in the biologic function of IFN-gamma. Polyclonal antibodies to either the N-terminal or the C-terminal peptides also inhibited both the antiviral and the macrophage-priming activities of IFN-gamma. All of the antibodies that inhibited IFN-gamma function also blocked binding of IFN-gamma to membrane receptor on cells, whereas antibodies that did not block function also did not inhibit binding. The data suggest that both the N-terminal and the C-terminal domains of IFN-gamma play an important role in its antiviral and macrophage-priming functions, possibly in a cooperative manner.

Amino Acid Sequence↗
PubMed1978

The final test.

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Education, Medical, Undergraduate↗