Neuroendocrine peptide hormone regulation of immunity.
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Animals↗
Biomedical subjects
H M Johnson
Publications and source records attributed to H M Johnson.
HIV encodes for its own CD4 T-cell superantigen mitogen.
Previously we reported that Nef protein from human immunodeficiency virus (HIV) induces proliferation of human peripheral blood mononuclear cells (PBMC). Herein, we show that HIV replicates in cells activated by Nef. PBMC proliferated in response to Nef and were capable of producing significant amounts of infectious virus upon infection. Polyclonal antibodies to Nef synthetic peptides blocked proliferation and neutralized infection. Characteristic of superantigens, T-cell proliferation in response to Nef required antigen-presenting cells and showed CD4 Vb preferences as previously shown. These findings suggest that Nef is a virally encoded T-cell superantigen and, as such, may be vital in the establishment of HIV infection in a new host and in subsequent disease pathogenesis.
Adult↗
Characterization of Nef-induced CD4 T cell proliferation.
Studies on Nef, a regulatory protein encoded by human immunodeficiency virus (HIV), suggest it plays an important role in HIV pathogenesis. Previously, we reported that Nef binds to class II MHC antigens and induces proliferation of human peripheral blood mononuclear cells (PBMC). Herein, we further characterize PBMC responses to Nef. Polyclonal antisera generated against Nef synthetic peptides blocked proliferation. Responses were T cell-specific and required antigen-presenting cells (APC). T cells responded in the presence of paraformaldehyde-inactivated APC, suggesting that Nef is presented in an unprocessed form. Nef-stimulated cells produced IL 2 and IFN gamma, products of T helper-1 cells. Thus, Nef has superantigen properties in that it binds to MHC class II antigens, does not need processing to be presented by APC, and activates T cells, causing proliferation and production of the T helper 1 cytokines, IL 2 and IFN gamma. The identification of an HIV protein that activates T cells is of considerable interest, given that HIV replicates in T cell blasts but not in quiescent cells.
Adult↗
A neutralizing epitope of the superantigen SEA has agonist activity on T cells.
We have previously shown that sequence 121-149 of the staphylococcal enterotoxin superantigen SEA plays an important role in superantigen function. A synthetic peptide of this region, SEA(121-149), blocks SEA binding to class II MHC molecules and induces interleukin-1 and tumor necrosis factor production in monocytes. In this study, we further emphasize the structural and functional significance of this region of SEA by showing that the SEA(121-149) peptide induces T cell proliferation in a manner similar to that of SEA. SEA(121-149) reacted with antibodies produced to SEA, and the SEA(121-149) specific antibodies neutralized SEA mitogenic activity. A tetrameric form of SEA(121-149) showed increased binding to antibodies and enhanced T cell activation, consistent with the greater avidity associated with increased valency. These data suggest that the internal domain of SEA corresponding to residues 121-149 plays an important role in superantigen activity.
Adult↗
Structural requirements for agonist activity of a murine interferon-gamma peptide.
We have demonstrated previously that murine interferon-gamma (MuIFN-gamma) binds to the extracellular domain of the receptor alpha chain through its N-terminus and subsequently to the cytoplasmic domain of the receptor via its C-terminus. Binding of the C-terminus to the cytoplasmic domain of the receptor is thought to occur following endocytosis of the IFN-gamma-receptor complex. In fact, the MuIFN-gamma C-terminus peptide, MuIFN-gamma (95-133), has full agonist activity on macrophages where it is internalized through pinocytosis. Here we examine the structural elements required for the agonist activity of MuIFN-gamma (95-133). Disruption of the alpha helical structure of the peptide by proline substitutions or truncation of the helix resulted in significant loss of binding or loss of antiviral activity or both and induction of MHC class II molecules. Further, removal of the polycationic sequence RKRKR in the tail beyond the helical structure also resulted in loss of agonist activity. Thus, we have isolated the functional site on MuIFN-gamma to the C-terminus and have shown that its helical structure and polycationic tail are required for binding to the cytoplasmic domain of the receptor and induction of biologic activity.
Adjuvants, Immunologic↗
Replication of HIV-1 in human peripheral blood mononuclear cells activated by exogenous Nef.
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Cells, Cultured↗
Superantigens: structure and relevance to human disease.
Superantigens are a class of immunostimulatory molecules produced by bacteria and viruses. Their potent immune effects are due to their unique ability to bind to the major histocompatibility complex (MHC) outside the antigen-binding cleft and to stimulate T cells in a T-cell receptor (TCR) Vbeta-specific manner. Structural studies have revealed the binding sites involved in the MHC/superantigen/TCR complex. The bacterial superantigens are responsible for a number of syndromes, including food poisoning and toxic shock syndrome, but their effects may be not only acute but also chronic and complex. Recent evidence suggests that superantigens may be relevant to the pathogenesis of autoimmune and immunodeficiency disorders. To illustrate the detrimental effects of superantigens on disease outcome, evidence demonstrating the modulation of experimental allergic encephalomyelitis, an animal model for multiple sclerosis, by superantigen, as well as the potential role of superantigens in HIV pathogenesis of AIDS, will be presented. The information presented may provide valuable insight into the role of superantigens in autoimmunity and HIV infection.
Animals↗
Differential recognition of the type I interferon receptor by interferons tau and alpha is responsible for their disparate cytotoxicities.
Interferon tau (IFN tau), originally identified as a pregnancy recognition hormone, is a type I interferon that is related to the various IFN alpha species (IFN alpha s). Ovine IFN tau has antiviral activity similar to that of human IFN alpha A on the Madin-Darby bovine kidney (MDBK) cell line and is equally effective in inhibiting cell proliferation. In this study, IFN tau was found to differ from IFN alpha A in that is was > 30-fold less toxic to MDBK cells at high concentrations. Excess IFN tau did not block the cytotoxicity of IFN alpha A on MDBK cells, suggesting that these two type I IFNs recognize the type I IFN receptor differently on these cells. In direct binding studies, 125I-IFN tau had a Kd of 3.90 x 10(-10) M for receptor on MDBK cells, whereas that of 125I-IFN alpha A was 4.45 x 10(-11) M. Consistent with the higher binding affinity, IFN alpha A was severalfold more effective than IFN tau in competitive binding against 125I-IFN tau to receptor on MDBK cells. Paradoxically, the two IFNs had similar specific antiviral activities on MDBK cells. However, maximal IFN antiviral activity required only fractional occupancy of receptors, whereas toxicity was associated with maximal receptor occupancy. Hence, IFN alpha A, with the higher binding affinity, was more toxic than IFN tau. The IFNs were similar in inducing the specific phosphorylation of the type I receptor-associated tyrosine kinase Tyk2, and the transcription factors Stat1 alpha and Stat2, suggesting that phosphorylation of these signal transduction proteins is not involved in the cellular toxicity associated with type I IFNs. Experiments using synthetic peptides suggest that differences in the interaction at the N terminal of IFN tau and IFN alpha with the type I receptor complex contribute significantly to differences in high-affinity equilibrium binding of these molecules. It is postulated that such a differential recognition of the receptor is responsible for the similar antiviral but different cytotoxic effects of these IFNs. Moreover, these data imply that receptors are "spare'' with respect to certain biological properties, and we speculate that IFNs may induce a concentration-dependent selective association of receptor subunits.
Animals↗
Identification of IFN-gamma receptor binding sites for JAK2 and enhancement of binding by IFN-gamma and its C-terminal peptide IFN-gamma(95-133).
The tyrosine kinase JAK2 is an integral part of the signal transduction pathways of a number of cytokines and growth factors, including IFN-gamma. Previously, we identified a species-nonspecific binding site for the C terminus of IFN-gamma, encompassed by IFN-gamma peptide IFN-gamma(95-133), on the membrane proximal region of the cytoplasmic domain of the IFN-gamma R alpha-chain. Using both a radioligand binding assay and coimmunoprecipitation with antireceptor antiserum, we were able to demonstrate specific interaction of JAK2 with the murine IFN-gamma R(MIR) alpha-chain. Furthermore, this interaction is increased by the addition of murine IFN-gamma or its C-terminal peptide, muIFN-gamma(95-133). We also identified two regions of the cytoplasmic domain of the receptor that interact with JAK2 using synthetic peptides of the MIR alpha-chain in receptor competition studies. These regions are encompassed by receptor peptide MIR(283-309), which is adjacent to the membrane proximal region at which the C terminus of IFN-gamma binds, and receptor peptide MIR(404-432), which lies near the C terminus of the receptor, encompassing a potentially important phosphorylation site. These data show site-specific interaction between JAK2 and IFN-gamma with the IFN-gamma R and have broader implications for the role of the IFN-gamma ligand in the IFN-gamma signal transduction pathway. Furthermore, the data support previous studies that demonstrated that intracellular IFN-gamma plays a role in cell activation.
Amino Acid Sequence↗
The IFN pregnancy recognition hormone IFN-tau blocks both development and superantigen reactivation of experimental allergic encephalomyelitis without associated toxicity.
Multiple sclerosis (MS) is an inflammatory demyelinating autoimmune disease if the central nervous system (CNS). Recently, the type I IFN, IFN-beta-1b was demonstrated to be a useful immunotherapy for MS. During treatment with IFN-beta-1b, toxicity at higher doses has been observed. IFN-tau, discovered for its role in the reproductive cycle, possesses all of the functions normally ascribed to the type I IFNs but lacks the toxicity normally associate with IFN treatment in vitro. We have examined the effects of IFN-tau treatment on experimental allergic encephalomyelitis (EAE), an animal model useful for the study of MS. EAE is a model of Ag-induced autoimmunity that can be modulated by bacterial superantigen to resemble the relapsing-remitting pattern of autoimmune disease observed in MS. IFN-tau was able to prevent development of EAE as effectively as IFN-beta but without associated toxicity such as lymphocyte suppression and weight loss. In addition, IFN-tau was able to prevent superantigen reactivation of EAE akin to the reduction in disease exacerbations observed in IFN-beta-1b treated MS patients. Mechanisms by which IFN-tau may prevent EAE include reduced proliferation in response to the autoantigen myelin basic protein and reduced TNF-alpha production. Thus, IFN-tau may prove to be a promising new IFN therapy for MS in light of its ability to prevent EAE and the lack of toxicity exhibited by this novel IFN.
Animals↗
Accelerated induction of experimental allergic encephalomyelitis in PL/J mice by a non-V beta 8-specific superantigen.
Superantigens such as the staphylococcal enterotoxins can play an important role in exacerbation of autoimmune disorders such as experimental allergic encephalomyelitis (EAE) in mice. In fact, superantigens can reactivate EAE in PL/J mice that have been sensitized to rat myelin basic protein (MBP). The T-cell subset predominantly responsible for disease in PL/J mice bears the V beta 8+ T-cell antigen receptor (TCR). The question arises as to whether T cells bearing other V beta specificities are involved in induction or reactivation of EAE with superantigen. Thus, we have investigated the ability of a non-V beta 8-specific superantigen, staphylococcal enterotoxin A (SEA) (V beta specificities 1, 3, 10, 11, and 17), to induce EAE in PL/J mice that have been previously protected from disease by anergy and deletion of V beta 8+ T cells. PL/J mice were first pretreated with the V beta 8-specific superantigen staphylococcal enterotoxin B (SEB) and then immunized with MBP. These mice exhibited V beta 8-specific anergy and depletion and did not develop EAE, even when further treated with SEB. However, administration of SEA to these same mice induced an initial episode of EAE which was characterized by severe hindleg paralysis and accelerated onset of disease. In contrast to SEB pretreatment, PL/J mice pretreated with SEA did develop EAE when immunized with MBP, and after resolution of clinical signs of disease these mice were susceptible to relapse of EAE induced by SEB but not by SEA. Thus, superantigens can activate encephalitogenic MBP-specific non-V beta 8+ T cells to cause EAE in PL/J mice. These data suggest that superantigens can play a central role in autoimmune disorders and that they introduce a profound complexity to autoimmune diseases such as EAE, akin to the complexity seen in multiple sclerosis.
Animals↗
Type I interferon inhibition of superantigen stimulation: implications for treatment of superantigen-associated disease.
The interferons (IFNs) are a family of secretory glycoproteins possessing potent antiviral, antiproliferative, antimicrobial, and immunomodulatory activities. It has been shown that the IFNs and superantigens have an important effect on the course of certain autoimmune disorders, and thus we have examined the effect of the type I and type II IFNs on superantigen-induced stimulation. The type I IFNs, alpha, beta, and tau, inhibited induction of T cell proliferation by several staphylococcal enterotoxin superantigens; the type II IFN, gamma, was without effect. The type I IFNs inhibited T cell proliferation to the same extent, approximately 50% at 10(3) units of IFN/ml, and in a dose-dependent manner. Consistent with inhibition of proliferation, the type I IFNs also inhibited IL-2 production as well as levels of IL-2 receptor expression. Inhibition was not increased by using the IFNs in combination, suggesting that they inhibited proliferation by the same mechanism. IFNs alpha and beta, but not IFN-tau, were toxic to cells at high concentrations (> or = 10(4) units/ml). Thus, the mechanism by which type I IFNs inhibit cell proliferation differs from that associated with their toxic effects. A partial reduction of V beta-specific superantigen-induced T cell expansion by type I IFNs was also demonstrated using flow cytometry. We recently showed that superantigens play an important role in the reactivation of experimental allergic encephalomyelitis. The potent antiproliferative activities of the type I IFNs strongly suggest the further study of their use as therapies for superantigen-associated diseases, such as multiple sclerosis and other autoimmune disorders, as well as toxic shock syndrome.
Autoimmune Diseases↗
Multiple binding sites on the superantigen, staphylococcal enterotoxin B, imparts versatility in binding to MHC class II molecules.
To determine MHC class II molecule binding regions of staphylococcal enterotoxin B (SEB), we employed a structurally based approach in which eight overlapping peptides of the entire SEB molecule were synthesized to encompass discrete secondary structures based on the SEB crystalline structure. SEB peptides encompassing amino acid residues 1-33, 31-64 and 179-212 successfully competed with [125I]SEB for binding to DR1 transfected L cells. In contrast, SEB peptides encompassing amino acid residues 1-33, 124-154, 150-183 and 179-212 successfully competed with [125I]SEB for binding to Raji cells (HLA-DR3, DRw10, DQw1 and DQw2). In addition, the SEB peptide (124-154) inhibited the mitogenic function of SEB. Thus, we have identified multiple regions, including the C-terminus, of SEB that are involved in binding to MHC class II and have shown that these interactions are complex and dependent on the haplotype of the MHC class II molecule.
Amino Acid Sequence↗
Binding of IFN gamma and its C-terminal peptide to a cytoplasmic domain of its receptor that is essential for function.
We have previously shown that murine interferon gamma (IFN gamma) binds to a soluble form of its receptor via both the N-terminus and C-terminus. The IFN gamma N-terminus binds extracellular receptor residues 95-120. Here we report that the C-terminus of IFN gamma binds to the membrane proximal region of the cytoplasmic domain of the receptor, residues 253-287. Peptide binding to fixed/permeabilized cells is specifically blocked by anti-(253-287) antibodies. These data suggest a novel mechanism by which IFN gamma binds to its receptor, involving both the extracellular and the intracellular receptor domains. Such a mechanism could have broader implications for the activation of signal transduction pathways by both IFN gamma and other cytokines whose receptors are members of the cytokine receptor superfamily.
Amino Acid Sequence↗
Identification of an HIV-1 Nef peptide that binds to HLA class II antigens.
Overlapping peptides corresponding to the entire Nef (HIVBRU) sequence were tested for their relative abilities to block binding of staphylococcal enterotoxins (SEs) to Raji cells. An internal sequence, Nef(123-160), blocked binding of two highly homologous SEs, SEA and SEE, while it was less effective against SEB and SEC1. Nef(123-160) bound directly class II DR antigens, as assessed by specific antibodies, and its binding was significantly inhibited by SEE, and also by SEA to a lesser degree. Purified Nef inhibited specific binding of SEA to Raji cells in a dose-dependent manner. Nef induced IL 2 production and proliferation by human mononuclear cells. Definitive expansion of specific V beta T cell populations was not observed, possibly due to lesser mitogenic activity of Nef relative to SEs. Thus, Nef may have mitogenic activity similar to that of superantigens.
Amino Acid Sequence↗
Complementary peptides as probes to explore neuropeptide receptors on lymphocytes.
Studies on neuroendocrine hormone receptor have been hampered by low numbers and concentrations of receptors found within and outside the neuroendocrine system. The complementary peptide approach is particularly useful for dealing with this problem and has been used to characterize lymphoid receptors for arginine vasopressin (AVP), corticotropin (ACTH), substance P, and opioid peptides. A nonapeptide derived by reading of the complementary DNA strand of the bovine AVP gene in the 3' to 5' direction specifically blocks the AVP helper signal for interferon-gamma production by mouse T lymphocytes. Antibodies to 3'-5' AVP-binding peptide bound to cells, and the binding was inhibited by excess AVP. Thus, binding of anti-3'-5'AVP-binding peptide antibodies to the AVP receptor was specific. The complementary peptide approach has also been used to produce antibodies specific for the ACTH receptor complex. Complementary peptides to ACTH derived by reading in either the 5' to 3' or 3' to 5' direction were able to bind to ACTH. Monospecific antibodies to the ACTH (1-24) complementary peptide caused an ACTH-like steroidogenic response of cultured mouse adrenal cells, presumably by binding to the ACTH receptor, and binding was specifically inhibited by ACTH. The ACTH receptor complex from solubilized adrenal cells was shown to consist of four subunits with M(r) 83,000, 64,000, 52,000, and 22,000. The 83,000 and 52,000 M(r) subunits are disulfide linked and noncovalently associated with the other subunits, with binding of labeled ACTH localized to the 83,000 M(r) subunit. Similarly, a complementary peptide was shown to bind directly to substance P in a saturable and dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Sequence↗
Can superantigens trigger sudden infant death?
A majority of sudden infant death syndrome (SIDS) victims have respiratory or gastrointestinal infections prior to death. This has led to an investigation of the role of pathogenic bacteria and the potentially lethal toxins they produce as triggers for sudden infant death. A small group of bacteria have been consistently identified in SIDS victims as compared to controls, and remarkably, three of these produce superantigenic toxins. Superantigens exert a powerful effect on the immune system, stimulating T-cells, which subsequently induces the formation of large amounts of cytokines. Generation of an overwhelming inflammatory response may lead to death by shock, or other, as yet unrecognized effects of the toxin on the respiratory or cardiac systems. A SIDS/superantigen model is proposed which may explain many of the pathological characteristics of SIDS and establish quantifiable markers for SIDS.
Bacterial Infections↗
How interferons fight disease.
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Animals↗