The V beta-specific superantigen staphylococcal enterotoxin B: stimulation of mature T cells and clonal deletion in neonatal mice

TCR expression and clonality analysis in peripheral blood and lymph nodes of HIV-infected patients

We compared the T cell receptor (TCR) V beta gene family repertoire in peripheral blood mononuclear cells (PBMC) and lymph node (LN) cells from 7 human immunodeficiency virus (HIV)-infected patients and 3 seronegative healthy controls. Virtually all the V beta family specificities were represented in patient PBMC and LN cells, and mean values for each specificity were comparable to figures in seronegative controls. In 4 patients, however, some V beta gene segment transcripts were overrepresented in the LN compartment, compared to the peripheral blood counterpart. To ascertain whether this phenomenon was due to polyclonal or oligoclonal expansion of T cells bearing the relevant V beta gene product, we sequenced the entire CDR3 region of a panel of 238 PCR clones corresponding to the V beta transcripts expanded in LN; as control, the same regions were cloned and sequenced in patient's PBMC, and in PBMC and LN cells from seronegative individuals. This analysis disclosed preferential usage of J beta 2 genes in PBMC and LN cells from both seropositive patients and controls, regardless of the V beta gene segment considered, thus indicating that this skewness in the V beta-J beta repertoire could be a consistent feature of at least a part of the V beta repertoire in different lymphoid compartments, regardless of the pathologic conditions. In addition, in LN from HIV seropositive patients we found the presence of recurrent TCR rearrangements, accounting for 8-23% of the generated clones, in each of the 4 V beta specificities analyzed; recurrent sequences were not found in PBMC from patients nor in PBMC and LN cells from seronegative controls. These findings suggest that antigen-driven oligoclonal T cell expansions may occur in vivo in lymphoid organs of HIV seropositive patients.

A human endogenous retroviral superantigen as candidate autoimmune gene in type I diabetes

Microbial superantigens (SAGs) have been implicated in the pathogenesis of human autoimmune diseases. Preferential expansion of the Vveta7 T cell receptor positive T cell subset in patients suffering from acute-onset type I diabetes has indicated the presence of a surface membrane-bound SAG. Here, we have isolated a novel mouse mammary tumor virus-related human endogenous retrovirus. We further show that the N-terminal moiety of the envelope gene encodes an MHC class II-dependent SAG. We propose that expression of this SAG, induced in extrapancreatic and professional antigen-presenting cells, leads to beta-cell destruction via the systemic activation of autoreactive T cells. The SAG encoded by this novel retrovirus thus constitutes a candidate autoimmune gene in type I diabetes.

A structural and functional comparison of staphylococcal enterotoxins A and C2 reveals remarkable similarity and dissimilarity

Staphylococcal enterotoxins and toxic shock syndrome toxin-1 are known as superantigens due to their ability to activate a large number of T-cells by crosslinking the major histocompatibility complex class II molecules with the T-cell receptor. Although superantigens seem to act by a common mechanism, they vary in many of their specific interactions and biological properties. A structural comparison of staphylococcal enterotoxins A and C2, members of the staphylococcal superantigens, has shown large conformational differences at the putative TcR interaction site (loops between alphaN-alpha2, alpha4-beta9 and beta10-alpha5 in staphylococcal enterotoxin A) that could explain the variability in their T-cell receptor specificity. A common Zn2(+)-binding site was identified in both staphylococcal enterotoxin A and C2 that is superimposable but differs somewhat in its coordination geometry between the two molecules.

Influence of the NH2-terminal amino acid of the T cell receptor alpha chain on major histocompatibility complex (MHC) class II + peptide recognition

The alpha/beta T cell receptor (TCR) recognizes peptide fragments bound in the groove of major histocompatibility complex (MHC) molecules. We modified the TCR alpha chain from a mouse T cell hybridoma and tested its ability to reconstitute TCR expression and function in an alpha chain-deficient variant of the hybridoma. The modified alpha chain differed from wild type only in its leader peptide and mature NH2-terminal amino acid. Reconstituted cell surface TCR complexes reacted normally with anti-TCR and anti-CD3 antibodies. Although cross-linking of this TCR with an antibody to the TCR idiotype elicited vigorous T cell hybridoma activation, stimulation with its natural MHC + peptide ligand did not. We demonstrated that this phenotype could be reproduced simply by substituting the glutamic acid (E) at the mature NH2 terminus of the wild type TCR alpha chain with aspartic acid (D). The substitution also dramatically reduced the affinity of soluble alpha/beta-TCR heterodimers for soluble MHC + peptide molecules in a cell-free system, suggesting that it did not exert its effect simply by disrupting TCR interactions with accessory molecules on the hybridoma. These results demonstrate for the first time that amino acids which are not in the canonical TCR complementarity determining regions can be critical in determining how the TCR engages MHC + peptide.

Expression of bacterial superantigen genes in mice induces localized mononuclear cell inflammatory responses

Bacterial superantigens are potent T cell activators, and superantigen proteins have been injected into mice and other animals to study T cell responses in vivo. When superantigen proteins are injected, however, the T cell stimulatory effects cannot be confined to specific tissues. Therefore, to target superantigen expression to specific tissues, we used gene transfer techniques to express bacterial superantigen genes in mammalian cells in vitro and in tissues in vivo. Murine, human, and canine cells transfected with superantigen genes in vitro all produced superantigen proteins both intracellularly and extracellularly, as assessed by bioassay, immunocytochemistry, and antigen ELISA. Superantigens produced by transfected eukaryotic cells retained their biologic specificity for T cell receptor binding. Intramuscular injection of superantigen plasmid DNA in vivo induced an intense intramuscular mononuclear cell infiltrate, an effect that could not be reproduced by intramuscular injection of superantigen protein. Intradermal and intravenous injection of superantigen DNA induced cutaneous and intrapulmonary mononuclear cell inflammatory responses, respectively. Thus, superantigen genes can be expressed by mammalian cells in vivo. Superantigen gene therapy represents a novel method of targeting localized T cell inflammatory reactions, with potential application to treatment of cancer and certain infectious diseases.

Pathogenesis of an infectious mononucleosis-like disease induced by a murine gamma-herpesvirus: role for a viral superantigen?

The murine gamma-herpesvirus 68 has many similarities to EBV, and induces a syndrome comparable to infectious mononucleosis (IM). The frequency of activated CD8+ T cells (CD62L(lo)) in the peripheral blood increased greater than fourfold by 21 d after infection of C57BL/6J (H-2(b)) mice, and remained high for at least a further month. The spectrum of T cell receptor usage was greatly skewed, with as many as 75% of the CD8+ T cells in the blood expressing a Vbeta4+ phenotype. Interestingly, the Vbeta4 dominance was also seen, to varying extents, in H-2(k), H-2(d), H-2(u), and H-2(q) strains of mice. In addition, although CD4 depletion from day 11 had no effect on the Vbeta4 bias of the T cells, the Vbeta4+CD8+ expansion was absent in H-2IA(b)-deficient congenic mice. However, the numbers of cycling cells in the CD4 antibody-depleted mice and mice that are CD4 deficient as a consequence of the deletion of MHC class II, were generally lower. The findings suggest that the IM-like disease is driven both by cytokines provided by CD4+ T cells and by a viral superantigen presented by MHC class II glycoproteins to Vbeta4+CD8+ T cells.

Transcytosis of staphylococcal superantigen toxins

Staphylococcus aureus produces a set of proteins (e.g., staphylococcal enterotoxin A [SEA], SEB, toxic shock syndrome toxin 1 [TSST-1]) which act both as superantigens (SAgs) and toxins. Although their mode of action as SAgs is well understood, little is known about how they enter the body via the intestine and cause food poisoning. To examine this problem we used an in vitro culture system to study the capacity of class II MHC-negative human intestinal epithelial cells (Caco-2) to transcytose several staphylococcal toxins. We found that Caco-2 cells are capable of dose-dependent, facilitated transcytosis of SEB and TSST-1, but not SEA. We extended these studies in vivo in mice by showing that ingested SEB appears in the blood more efficiently than SEA. Our data suggest that these toxins can cross the epithelium in an immunologically intact form. These results may have important implications for the pathogenesis of food poisoning.

Clinical role for a superantigen in Yersinia pseudotuberculosis infection

Yersinia pseudotuberculosis is an enteric pathogen that causes a variety of clinical symptoms in the human. Recently, we reported the production of a superantigen (Y. pseudotuberculosis-derived mitogen, YPM) by this organism and characterized the gene structure of ypm. To further study the potential pathogenic role of YPM in Y. pseudotuberculosis infection, we assayed IgG anti-YPM antibodies and T cell antigen receptor-Vbeta expression of the T cells in peripheral blood and in mesenteric lymph node in patients acutely infected with Y. pseudotuberculosis. 20 out of 33 patients (61%) had an elevated antibody titer compared with healthy controls (P = 0.0001). Patients with systemic symptoms such as lymphadenopathy, transient renal dysfunction, and arthritis had significantly higher titers of anti-YPM than patients with gastrointestinal tract symptoms alone. T cells bearing the Vbeta3 gene segment were significantly increased (P = 0.009) among acute phase patients compared with healthy children. During the convalescence phase of the illness, there was a reduction in the abnormal level of Vbeta3 T cells. Moreover, in the mesenteric lymph node, an elevated level of Vbeta3 T cells compared with peripheral blood and a sequence diversity in the junctional region of the T cell antigen receptor beta-chain containing Vbeta3 element was observed in one patient. Together, these findings suggest that YPM was produced in vivo and played an important role in the pathogenesis of Y. pseudotuberculosis infection.

Molecular mechanisms and selective influences that shape the kappa gene repertoire of IgM+ B cells

To analyze the human kappa chain repertoire and the influences that shape it, a single cell PCR technique was used that amplified Vkappa Jkappa rearrangements from genomic DNA of individual human B cells. More than 350 productive and 250 nonproductive Vkappa Jkappa rearrangements were sequenced. Nearly every functional Vkappa gene segment was used in rearrangements, although six Vkappa gene segments, A27, L2, L6, L12a, A17, and O12/O2 were used preferentially. Of these, A27, L2, L6, and L12a showed evidence of positive selection based on the variable region and not CDR3, whereas A17 was overrepresented because of a rearrangement bias based on molecular mechanisms. Utilization of Jkappa segments was also nonrandom, with Jkappa1 and Jkappa2 being overrepresented and Jkappa3 and Jkappa5 underrepresented in the nonproductive repertoire, implying a molecular basis for the bias. In B cells with two Vkappa Jkappa rearrangements, marked differences were noted in the Vkappa segments used for the initial and subsequent rearrangements, whereas Jkappa segments were used comparably. Junctional diversity was generated by n-nucleotide addition in 60% and by exonuclease trimming in 75% of the Vkappa Jkappa rearrangements analyzed. Despite this large degree of diversity, a strict CDR3 length was maintained in both productive and nonproductive rearrangements. More than 23% of the productive rearrangements, but only 7% of the nonproductive rearrangements contained somatic hypermutations. Mutations were significantly more frequent in Vkappa sequences derived from CD5- as compared with CD5+ B cells. These results document that the gene segment utilization within the Vkappa repertoire is biased by both intrinsic molecular processes as well as selection after light chain expression. Moreover, IgM+ memory cells with highly mutated kappa genes reside within the CD5- but not the CD5+ B cell compartment.

Superantigen and endotoxin synergize in the induction of lethal shock

Endotoxin (lipopolysaccharide; LPS) and superantigens (exotoxins) have been identified as potent inducers of lethal shock. While endotoxin primarily interacts with CD14 receptors on macrophages, superantigens like the staphylococcal enterotoxin B (SEB) preferentially activate T cells. Both cell types are triggered to release pro-inflammatory cytokines that in turn induce lethal shock. We analyzed whether endotoxin and superantigen interact during the induction phase of lethal shock. We report that LPS and SEB operate synergistically. Lethal doses of both inducers were reduced 100-fold when given in combination. The induced serum levels of tumor necrosis factor, interleukin-6, and interferon-gamma (IFN-gamma) were elevated and remained high for a prolonged period. Moreover, synergistic action of LPS and SEB induced lethal toxic shock even without presensitization of mice with D-galactosamine (D-GalN). Opposed to D-GalN-pretreated mice, mice injected with LPS and SEB showed less liver damage, but rather apoptosis of epithelial cells in the bowel. Cyclosporin A and treatment with anti-IFN-gamma monoclonal antibody blocked the synergistic action of LPS and SEB, indicating that T cell-derived IFN-gamma is the mediator of the observed synergism. Concomitant injection of LPS and SEB had no influence on SEB-induced T cell deletion and anergy induction. Since Gram-positive and Gram-negative bacteria can be recovered from septic blood samples, the synergistic action of endotoxin and superantigens might be relevant during lethal septicemia.

The agonist-antagonist balance in positive selection

Peptide antigens expressed in the thymus, in combination with self major histocompatibility complex molecules play a crucial role in thymocyte selection and shaping of the mature T-cell repertoire. Here, it is proposed that a single thymocyte may be exposed to numerous different peptide ligands as it matures, such that its fate is determined by the sum of signals produced by these interactions.

Characteristics and maintenance of CD8+ T-cell clones found in old mice

Old mice, like old human beings, contain large clones of CD8+ T-cells. These cells grow poorly in tissue culture, therefore it is difficult to maintain the cells in vitro. The cells can be grown after transfer to sublethally irradiated mice. This technique will be useful in further studies on the properties of the cells. Based on observations from such transfer experiments, we conclude that: (1) expansion of the T-cell clones in recipients is dramatic but slow; (2) chance events caused by endogenous antigens or gene mutations rather than exogenous antigens may account for the expansion of these clones; and (3) the expanded T-cell clones are benign and do not cause malignancies.

Superantigen-induced stromelysin production from rheumatoid synovial cells

Superantigens activate a large number of T cells in a V beta-restricted manner after binding to MHC class II molecules on the antigen presenting cells (APC). Superantigens also activate APC directly by interacting with their ligands, MHC class II molecules. In the present study, we examined the effects of superantigens on matrix metalloproteinases (MMPs) secretion from rheumatoid synovial fibroblasts. We demonstrated that stimulation of interferon (IFN)-gamma-treated synovial fibroblasts with staphylococcal enterotoxin A (SEA) selectively induced the secretion of stromelysin, a neutral MMP, from synovial fibroblasts. Pretreatment of synovial fibroblasts with cycloheximide, an inhibitor of protein synthesis, prevented MMP-3 secretion from rheumatoid synovial cells suggesting that protein synthesis was required for SEA-induced MMP-3 secretion after SEA binding to MHC class II molecules. Our data suggest that in the synovium, bacterial superantigens are potent inducers of stromelysin which plays a critical role in articular destruction observed in inflammatory joint disease.

V beta 8+CD4-CD8- subpopulation induced by staphylococcal enterotoxin B

Injection of staphylococcal enterotoxin B (SEB) into BALB/c mice induced the depletion of V beta 8+ T-cells which were either V beta 8+CD4+ or V beta 8+CD8+ cells. The CD8 molecule on V beta 8+CD8+ cells was found to decrease at 72 h after SEB treatment while the V beta 8 molecule on V beta 8+ cells or CD4 molecule on V beta 8+CD4+ cells was not affected. Furthermore, a subpopulation of V beta 8+CD4-CD8- T-cells was also induced after SEB-priming. This subpopulation can be found in spleen or lymph nodes. It was small in size and constituted the major part of V beta 8+ cells in lymph nodes at 72 h after SEB-priming. Some of the V beta 8+CD4-CD8- T-cells might be autoreactive because they could be stimulated to proliferative by syngenic mitomycin C-treated splenocytes.

Shared promoter elements between a viral superantigen and the major histocompatibility complex class II-associated invariant chain

Superantigens have the ability to stimulate subsets of T lymphocytes bearing particular T-cell receptor Vbeta chains. The best-known viral superantigen is Mls, a product of the murine mammary tumor virus (MMTV) sag gene. The MMTV superantigen is not displayed by the virus itself; however, after infection of B lymphocytes, the superantigen is expressed. The resulting immune stimulation is essential for viral transmission. We have analyzed the transcriptional elements which control Mls-1 expression. Here we present evidence that a region at the 3' end of Mtv-7 env, Penv2, controls B-cell-specific expression of sag. Penv2 has elements homologous with promoters of immunoglobulin H chain, the invariant chain, and major histocompatibility complex class II, suggesting a coordinate regulation of expression of these various B-cell-specific genes and indicating a possible eukaryotic origin of MMTV sag. We have determined that both an IgH heptamer element and a Y box are essential for Penv2 promoter activity and that tandem octamer motifs in the U3 region of the 3' MMTV long terminal repeat function as enhancers. We propose that Penv2 controls constitutive Mls expression in B lymphocytes.

Loss of T cell receptor Vbeta repertoires in HIV type 1-infected SCID-hu mice

Late-stage HIV-1 disease in humans has been associated with perturbations of the T cell receptor (TCR) Vbeta repertoire. It is not known if the observed loss of certain Vbeta families is attributable directly to HIV-1 infection or whether this is a consequence of multiple opportunistic infections. Putative HIV-1-associated superantigens have been postulated to be the cause of the perturbed TCR Vbeta repertoire and the subsequent CD4+ T cell depletion in HIV-1-infected humans. In this study, we examined the human TCR Vbeta repertoire in SCID-hu mice, housed in a pathogen-free environment and infected with a molecularly cloned virus strain, to ascertain directly the effect of HIV-1 on the human TCR Vbeta repertoire in the absence of other infectious agents. We demonstrate that mock-infected human thymus/liver (Thy/Liv) implants in SCID-hu mice have complete TCR Vbeta repertoires, reflective of a normal human thymus. However, HIV-1-infected implants in SCID-hu mice had depleted TCR Vbeta repertoires, corresponding with thymocyte depletion. These results indicate that HIV-1-specific mechanisms are the cause of the TCR Vbeta repertoire depletion in infected implants. However, these thymocyte depletions were not restricted to specific TCR Vbeta subsets. These results are not consistent with the hypothesis that HIV-1 acts as a superantigen in vivo. The disruption of the TCR Vbeta repertoire in the human Thy/Liv implants of the SCID-hu mice suggests that HIV-1 infection may be influencing T cell development in the thymus, contributing to both the overall CD4+ T cell depletion in AIDS and limited TCR repertoire diversity.

Identification of antigenic sites on staphylococcal enterotoxin B and toxoid

The staphylococcal enterotoxins (SEs) are capable of causing both food poisoning and a toxic shock-like illness in man. In addition, SEs are known to act as superantigens, stimulating T-cells according to their T-cell receptor Vbeta type. Relatively little is known of their antigenic determinants and how these may relate to the structure and function of the toxins. As a step in the study of these relationships, the entire molecule of SEB was synthesized in duplicate as a series of octapeptides overlapping by seven residues. This series thus represented all the potential linear epitopes of eight residues or less. The reactivity of the octapeptide series with antisera raised to purified SEB and to formaldehyde-inactivated SEB has been used to locate several antigenic sites on native SEB and to identify antigenic differences in the toxoid. Three antigenic peptides identified from the antigenic profile were synthesized and characterized. These represented amino acids 21-32, 93-107 and 202-217 of SEB. None of these peptides affected SEB-induced T-cell proliferation. However, the occurrence or absence of cross-reactivity of these peptides with antibodies to native SEB corresponds to the degree of exposure and/or the rigidity of these regions within SEB.

B cell superantigens in HIV-1 infection

HIV-I infection affects many of the cellular components vital for the maintenance of immune homeostasis. Similar to the T cell superantigen effect on T cell expansion and depletion in AIDS. HIV components with B cell superantigenic properties could be responsible for the observed B cell activation and skewing of VH family usage. Current data on possible B cell superantigen properties of HIV proteins (gp120) are mostly based on studies describing the clonality and VH family usage of immunoglobulins in HIV infection. Various laboratories reported independently an unusual skewing of the VH-repertoire of antibodies that appears not to be random. According to these observations, an enrichment of VH1 and VH4 family-paralleled a depletion of VH3 family-utilizing anti-HIV-1 gp120 and p24 antibodies in HIV-1 infected individuals and a loss of total VH3+ Ig in patients with late stages of AIDS. Polyclonal and monoclonal (VH1, VH4, and VH5) anti-p24 and gp120 antibodies share a crossreactive idiotype (IF7). IF7 like antibodies were found in the serum of HIV-1 infected individuals, persisting in the course of infection, perhaps contributing to the depletion of VH3 Ig. Furthermore a restriction of clonal heterogeneity of anti-p24 and anti-gp120 antibodies was detected by isoelectric focusing and indicated by skewed kappa/lambda light chain isotype ratios, indicating clonal dominance of certain sets of anti-HIV-1 antibodies during infection. Taken these findings together, a strong case for the involvement of a B cell superantigen can be made, although the mechanism of B cell depletion is not fully understood.

B-cell superantigens: molecular and cellular implications

B cell superantigens are proteins that are capable of immunoglobulin variable region mediated binding interactions with the naive B cell repertoire at frequencies that are orders of magnitude greater than occur for conventional antigens. Within this review we discuss recent observations regarding the molecular basis of these interactions and the distribution of superantigen binding capacities in different human B cell populations. These findings and current predictions regarding the relevance of these proteins to the physiologic development of immune repertoires are also discussed.

Identification of murine T cells reactive with the bacterial superantigen Yersinia pseudotuberculosis-derived mitogen (YPM) and factors involved in YPM-induced toxicity in mice

We previously reported that Yersinia pseudotuberculosis-derived mitogen (YPM) acts as a superantigen to human T cells. In this study, we assessed the superantigenicity and toxicity of YPM using murine experimental models. YPM activated T cells to produce interleukin-2 in a major histocompatibility complex class II molecule-dependent manner. The T-cell blasts induced by YPM expressed T-cell receptor (TCR) beta-chain variable region (Vbeta)7, Vbeta8.1, Vbeta8.2 and Vbeta8.3. The injection of YPM into mice pre-sensitized with D-galactosamine induced lethal shock. This shock was blocked by the injection of monoclonal antibodies (mAbs) to CD4, TCR Vbeta7 plus Vbeta8, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), but not by injection to CD8 or unrelated Vbeta. These results indicate that YPM-induced shock requires the presence of CD4+ T cells bearing TCR Vbeta7 and Vbeta8, and that endogenous TNF-alpha and IFN-gamma mediate the lethal effects.

Staphylococcal protein A binding to VH3 encoded immunoglobulins

Staphylococcal protein A (SPA) is a B-cell superantigen which binds specifically to the variable region of human VH3 encoded antibodies. We undertook to identify the VH3 regions involved in the interaction with SPA by producing mutant antibodies in the baculovirus expression system. We had previously shown that a single amino acid change at position 57 in the CDR2 of a human SPA nonbinding VH3 encoded rheumatoid factor converted it to an SPA binder, implicating CDR2 in SPA binding. When regions of the mutated binder were exchanged with those from a mouse nonbinding antibody, the pattern of SPA binding indicated that residues in FR1, CDR2 and FR3 are involved in the interaction between VH3 encoded antibodies and SPA. In addition, all three regions are simultaneously required for SPA binding to occur. When any one of the three regions was altered, SPA binding was severely disrupted.

TCR V beta gene expression in lesional T lymphocyte cell lines in oral lichen planus

To study V beta gene expression in oral lichen planus (OLP) lesional T lymphocytes cell lines.

MATERIALS AND METHODS

Lesional T lymphocytes were isolated from eight OLP patients and cell lines established. The total RNA was extracted from these lymphocyte cell lines and reverse transcribed. cDNA was amplified by the polymerase chain reaction (PCR) using a panel of 26 V beta-specific oligonucleotide primers followed by qualitative analysis of the electrophoresed reaction products.

RESULTS

V beta 1, 2, 3, 5.1, 6.1-3, 7, 8, 9, 22, 23, and 24 were represented consistently in all of the OLP samples, V beta 11, 12, and 17 were consistently negative, while the other V beta families (V beta 4, 5.2-3, 10, 13.1, 13.2, 14, 15, 16, 18, 19, 20, and 21) were variable. V beta 22 and 23 were the most strongly expressed in all patients.

CONCLUSIONS

A limited T cell receptor (TCR) gene usage indicates a degree of oligoclonality within these lesional T lymphocyte cell lines from OLP. This implies that OLP may be an antigen-specific disease or linked to a limited number of superantigens.

T cell selection and autoimmunity: flexibility and tuning

Peptide-MHC interactions govern the fate of T cells in the thymus and the peripheral T cell repertoire. Recent progress has involved investigating how different peptides influence T cell selection and mature T cell function and the subsequent implications for tolerance and autoimmunity.

Prior exposure to superantigen can inhibit or exacerbate autoimmune encephalomyelitis: T-cell repertoire engaged by the autoantigen determines clinical outcome

Experimental allergic encephalomyelitis (EAE) is inducible in experimental animals immunized with myelin basic protein (MBP), proteolipid protein (PLP) or their peptides. We compared T-cell responses to encephalitogenic epitopes of PLP(43-64) and MBP(Ac1-11) in a single mouse strain, (PL/J x SJL)F1. MBP(1-11)-specific T-cell hybridomas expressed predominantly TCR V beta 8 or V beta 4, while PLP(43-64)-specific hybridomas expressed a diverse TCR repertoire. To analyze the biologic significance of the TCR repertoire (limited vs. diverse) to disease susceptibility, we pretreated mice with a superantigen (SEB), and then induced disease with these autoantigens. Mice injected with SEB and immunized with MBP(Ac1-11) showed significant inhibition of EAE, whereas SEB-pretreated mice immunized with PLP(43-64) had an increased severity of EAE and developed a chronic disease. These data demonstrate that prior exposure to microbial superantigens can significantly alter the autoimmune disease course depending upon the TCR repertoire used by the autoantigen.

Defective depletion of CD45-null thymocytes by the Staphylococcus aureus enterotoxin B superantigen

The development of a normal T-cell repertoire is critically dependent on the negative and positive selection events which occur at the CD4+CD8+ (double positive, DP) stage of thymic development. Depending on the avidity of the T-cell antigen receptor (TCR) for peptides presented within the thymus, DP thymocytes are either positively selected for maturation to CD4+/CD8+ single positive cells or are depleted by apoptosis. The addition of superantigen to thymocytes within foetal thymic organ culture (FTOC) mimics the negative selection signal of potentially autoreactive thymocytes and induces the responding population of thymocytes to apoptose. Here we present evidence that the transmembrane phosphotyrosine phosphatase CD45 critically regulates TCR-induced signals in thymic differentiation and present data to show defective depletion of CD45-null transgenic TCR-Vbeta8 DP thymocytes in FTOC by the Staphylococcus aureus Enterotoxin B (SEB) superantigen.

Immunogenicity and efficacy against lethal aerosol staphylococcal enterotoxin B challenge in monkeys by intramuscular and respiratory delivery of proteosome-toxoid vaccines

Staphylococcal enterotoxin B (SEB), a primary cause of food poisoning, is also a superantigen that can cause toxic shock after traumatic or surgical staphylococcal wound [correction of would] infections or viral influenza-associated staphylococcal superinfections or when aerosolized for use as a potential biologic warfare threat agent. Intranasal or intramuscular (i.m.) immunization with formalinized SEB toxoid formulated with meningococcal outer membrane protein proteosomes has previously been shown to be immunogenic and protective against lethal respiratory or parenteral SEB challenge in murine models of SEB intoxication. Here, it is demonstrated that immunization of nonhuman primates with the proteosome-SEB toxoid vaccine is safe, immunogenic, and protective against lethal aerosol challenge with 15 50% lethal doses of SEB. Monkeys (10 per group) were primed i.m. and given booster injections by either the i.m. or intratracheal route without adverse side effects. Anamnestic anti-SEB serum immunoglobulin G (IgG) responses were elicited in all monkeys, but strong IgA responses in sera and bronchial secretions were elicited both pre- and post-SEB challenge only in monkeys given booster injections intratracheally. The proteosome-SEB toxoid vaccine was efficacious by both routes in protecting 100% of monkeys against severe symptomatology and death from aerosolized-SEB intoxication. These data confirm the safety, immunogenicity, and efficacy in monkeys of parenteral and respiratory vaccination with the proteosome-SEB toxoid, thereby supporting clinical trials of this vaccine in humans. The safety and enhancement of both bronchial and systemic IgA and IgG responses by the proteosome vaccine delivered by a respiratory route are also encouraging for the development of mucosally delivered proteosome vaccines to protect against SEB and other toxic or infectious respiratory pathogens.

Expression of T-cell receptor V beta 2 and type 1 helper T-cell-related cytokine mRNA in streptococcal pyrogenic exotoxin-C-activated human peripheral blood mononuclear cells

Streptococcal pyrogenic exotoxin type C (SPE C) is a member of the bacterial superantigens that are potent stimulants of T cells. We expressed SPE C in Escherichia coli and characterized its selective stimulation properties on human T cells bearing specific V beta chains of T-cell receptors (TCRs). Cytokine profiles induced by SPE C were also examined. Recombinant SPE C significantly enhanced proliferation of human peripheral blood mononuclear cells (PBMCs) at concentrations as low as 10(-12)-10(-14)M. Reverse transcription of RNA, from SPE-C-stimulated PBMCs followed by polymerase chain reaction, revealed selective induction of TCR V beta 2 chain expression. SPE C raised the mRNA level of type 1 helper T cell (TH1) related cytokines, such as interferon gamma (IFN-gamma), interleukin 2 (IL-2), and tumor necrosis factor beta (TNF beta). The expression of TNF alpha was also increased. In contrast, the increase in mRNA levels of the p35 small fragment of IL-12 and type 2 helper T cell (TH2) related cytokines (i.e., IL-4 and IL-10) was not significantly affected by SPE C. The mRNA level of proinflammatory cytokine IL-6 was increased marginally. Consistent with the mRNA accumulation, protein concentrations of IFN gamma, IL-2, and TNF were increased in SPE-C-stimulated PBMCs, but IL-4 was not. From these results, we conclude that the stimuli of SPE C preferentially causes the TH1 responses in human T cells bearing TCR V beta 2.

Proteins in the cell wall and membrane of Cryptococcus neoformans stimulate lymphocytes from both adults and fetal cord blood to proliferate

Cryptococcus neoformans is an encapsulated yeast that infects patients who have defective cell-mediated immunity, including AIDS, but rarely infects individuals who have intact cell-mediated immunity. Studies of the immune response to C. neoformans have been hampered by a paucity of defined T-lymphocyte antigens, and hence, the understanding of the T-cell response is incomplete. The goal of this study was to separate C. neoformans into its component parts, determine whether those components stimulate lymphocyte proliferation, perform preliminary characterization of the proteins, and establish the potential mechanism of lymphocyte proliferation. The lymphocyte response to fungal culture medium, whole organisms, disrupted organisms, and the yeast intracellular fraction or cell wall and membrane was studied by determining thymidine incorporation and by determining the number of lymphocytes at various times after stimulation. The cell wall and membrane of C. neoformans stimulated lymphocyte proliferation, while the intracellular fraction and culture filtrate did not. The optimal response occurred on day 7 of incubation, with 4 x 10(5) peripheral blood mononuclear cells per well and with 13 microg of cryptococcal protein per ml. The number of lymphocytes increased with time in culture, indicating that thymidine incorporation was accompanied by proliferation. Proteinase K treatment of the cell wall and membrane abrogated lymphocyte proliferation, indicating that the molecule was a protein. [35S]methionine labeling, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and fluorography were performed to analyze the proteins contained in the cell wall and membrane, intracellular fraction, and culture filtrate. At least 18 discrete bands were resolved from the cell wall and membrane. Since a large percentage of healthy adults responded to the cryptococcal cell wall and membrane, a mitogenic effect was investigated by testing proliferation of fetal cord blood lymphocytes. The percentage of fetal samples that proliferated in response to the cell wall and membrane was similar to the percentage of fetal samples that proliferated in response to Staphylococcus enterotoxin B, a microbial mitogen. Thus, a protein in the cell wall and membrane of C. neoformans is a potent stimulant of lymphocyte proliferation and has mitogenic properties, which may have important implications for cell-mediated immunity to C. neoformans.

Definition of the mitogenic factor (MF) as a novel streptococcal superantigen that is different from streptococcal pyrogenic exotoxins A, B, and C

Human T cell activation by recombinant mitogenic factor (rMF) was investigated in comparison with that by recombinant streptococcal pyrogenic exotoxins (rSPE) A, B, and C. Recombinant MF, rSPEA, and rSPEC were mitogenic for peripheral blood mononuclear cells (PBMC), whereas rSPEB was not. Recombinant MF required only HLA-DR for the stimulation of PBMC, as determined using monoclonal antibodies (mAb) to HLA class II molecules and the mouse L cells transfected with HLA class II molecules. Recombinant SPEA and rSPEC required HLA-DR or HLA-DQ molecule. Recombinant MF selectively stimulated V beta 2, V beta 7, V beta 8, V beta 18 and V beta 21-bearing T cells, whereas rSPEA and rSPEC activated V beta 2 and V beta 6-bearing T cells as evaluated by the quantitative T cell receptor (TCR) analytical method. No clonality was observed in the nucleotide sequences of complementarity determining region 3 of TCR V beta in T cells responding to rMF. The profiles of cytokine production by PBMC in response to rMF, rSPEA, and rSPEC were quite similar. In summary, these results demonstrate that both HLA class II molecules and the TCR V beta required for rMF-mediated T cell activation are distinct from those required for rSPEA or rSPEC-mediated activation. Therefore, the MF is a novel streptococcal super-antigen which is different from SPEA, SPEB, and SPEC.

Functional activity of staphylococcal enterotoxin A requires interactions with both the alpha and beta chains of HLA-DR

The staphylococcal enterotoxins, SEA and SEE, bind one zinc atom per molecule of protein. The presence of this metal atom enhances the binding of the toxins to MHC class II molecules, presumably through an interaction with histidine 81 of the beta chain. L cell transfectants expressing HLA-DR1 and HLA-DR7 molecules, with mutations in either the alpha1 or beta1 domains, were tested for their ability to bind SEA and present it to T cells. Cells expressing DR1 molecules with alanine at positions 77, 78, 80, 83, 84 and 85, or serine at position 79 could all bind SEA and present it to either polyclonal or monoclonal T cells. Most point mutations within the alpha-helical portion of the DR7 beta chain had no effect on binding and presentation. However, substitution of histidine 81 with alanine, glutamate, or aspartate, abrogated SEA binding as well as T cell stimulation by the superantigen. This effect was also observed when the non-polymorphic aspartate, at position 76 was changed to alanine. Mutation of the asparagine at position 82 had an intermediate effect. Point mutations of the DR alpha chain had little effect on binding of SEA as determined by a flow cytometric assay. However, mutation of lysine at position 39 of the alpha chain and, to a lesser extent methionine at position 36, markedly decreased the ability of SEA to stimulate toxin-responsive mouse T cell hybridomas. Finally, the monoclonal antibody, L243 binds to the alpha chain of HLA-DR, and was able to block T cell activation by SEA without blocking SEA binding. These data support the model whereby HLA-DR has two binding sites for SEA. A low affinity site, present on the alpha chain, is required for T cell stimulation by the superantigen, but is insufficient to mediate toxin binding. High affinity binding of HLA-DR to SEA occurs solely through residues on the beta chain, including both histidine 81 and aspartate 76.

Rapid clearance of the bacterial superantigen staphylococcal enterotoxin B in vivo

Following bolus injection of the superantigen Staphylococcus enterotoxin B (SEB) into mice, ligand-reactive T cells are triggered to release toxic amounts of lymphokines. Subsequently, within 6 to 10 h ligand-reactive Vbeta8+ T cells become anergic and clonally expand and thereafter are deleted via apoptosis. Since the binding affinities of SEB to major histocompatibility complex (MHC) class II molecules are as low as 1.7 microM, the concentration of SEB in the fluid phase dictates the presentation via MHC class II molecules. Here, we study the pharmacokinetics of SEB in vivo and correlate pharmacokinetics with immunogenicity. We describe here how after a bolus injection of SEB, the superantigen becomes systemically distributed, with peak levels within 5 to 30 min in blood and in lymph nodes. Clearance occurs within 10 to 24 h, with the kidneys being a major route. To induce T-cell activation in vivo, SEB must be present in concentrations above 10(-4) microg/ml. These concentrations exist for only 15 h. Manifestation of functional outcomes such as anergy, clonal expansion, and clonal deletion begins after 24 h. We conclude that the SEB model system can be used to separate the phase of T-cell receptor ligation from the phase of manifestation of functional outcomes.

Immune response during tumor therapy with antibody-superantigen fusion proteins

To engineer superantigens (SAg) to express tumor reactivity, we genetically fused the Fab-part of the tumor-reactive MAb C215 and the bacterial SAg staphylococcal enterotoxin A (SEA). Treatment of mice carrying established lung micrometastases of the C215-transfected syngeneic B16 melanoma with 3-4 daily injections of C215Fab-SEA resulted in strong antitumor effects, while only moderate effects were seen when treatment was given every 4th day (intermittent treatment). High serum levels of IL-2, TNF-alpha, IFN-gamma and strong induction of CTLs (cytotoxic T lymphocytes) were noted after priming with the fusion protein. T cells responded well to 3 daily injections of C215Fab-SEA and then gradually entered a hyporesponsive state, characterized by a reduced ability to produce IL-2, TNF-alpha and IFN-gamma and failure to mediate cytotoxicity in vitro. Intermittent treatment was characterized by increased levels of IL-10, concomitant with accentuated loss of IL-2, TNF-alpha and IFN-gamma production. A 10-fold increase in SEA-reactive TCR V(beta)3+ CD4+ cells was observed in the spleen, while a loss of TCR V(beta)3+ CD8+ and V(beta)11+ CD8+ cells was noted. This is in striking contrast to injections of native SEA which induced a marked deletion of TCR V(beta)3+ CD4+ T cells, but not of CD8+ cells. Recovery of the TH1 cytokine profile occurred within 1-2 weeks, while restoration of cytotoxicity required several months and correlated with recovery of TCR V(beta)3+ CD8+ and TCR V(beta)11+ CD8+ T cells. These results show that the temporal relationship of SAg stimulations dictates the cytokine profile. Moreover, different mechanisms appear to regulate hyporesponsiveness in CD4+ and CD8+ T cells.

Restricted T-cell antigen receptor repertoire in bronchoalveolar T cells from normal humans

The repertoire of variable alpha (AV) and beta (BV) TCR genes was compared in the peripheral blood and BAL fluid of five healthy individuals. Rearranged TCR transcripts were amplified by a reverse transcription-polymerase chain reaction, using oligonucleotide primers specific for 22 AV and 24 BV gene families. Nearly all AV and BV gene families were expressed in BAL T cells at levels similar to those in blood T cells. The diversity of AV and BV gene repertoire was examined further, testing the distribution of nucleotide lengths of TCR junctional regions. Most V gene families had a normal distribution of junctional region lengths in both blood and BAL T cells. Some gene families, particularly AV21 and BV9 in BAL samples, had a skewed banding pattern, with fewer bands or predominance of several bands. The limited diversity in TCR junctional region lengths was more prominent in CD8+ T cells from BAL fluids than from blood. CD4+ T cells also contributed to the limited diversity in BAL T cells. The oligoclonal expansion of bronchoalveolar CD8+ T cells was confirmed by sequence analysis of AV21-constant alpha (AC) and BV9-BC junctional regions in the blood and BAL cells. The levels of V gene expression and the diversity of junctional region lengths were very similar in T cells obtained from three separate lobes of one donor. In general, skewed patterns of TCR junctional region lengths were not consistent over time two donors, over periods of 3 and 17 months. Together, these data show that the T-cell repertoire is diverse within the lungs of normal humans, except for an oligoclonal predominance of a few V gene families in both CD4+ and CD8+ T cells. The T-cell repertoire in the lungs changes over time, which may reflect environmental exposures.

Unopposed positive selection and autoreactivity in mice expressing class II MHC only on thymic cortex

The normal development of T cells in the thymus requires both positive and negative selection. During positive selection, thymocytes mature only if their T-cell receptors react with some specificity to host major histocompatibility complex (MHC) and host peptides. During negative selection, thymocytes die if their T-cell receptors react with too high an affinity to the presenting cell, self MHC, and peptides to which they are exposed. These two processes are important for the development of the T-cell repertoire and the acquisition of self-tolerance, but their precise location and temporal relationship are not known. We have used the keratin 14 (K14) promoter to re-express a class II MHC antigen (I-Ab) in class II-negative mice. The transgenic I-A molecule is expressed only on thymic cortical epithelium; thymic medullary epithelium and bone-marrow-derived cells are I-A negative. CD4+ cells are positively selected in K14 mice, but clonal deletion does not ocur in K14 mice or in relB-negative mice, which lack a thymic medulla. The K14 CD4 cells are autoreactive, as they proliferate extensively to and specifically lyse I-Ab-positive target cells. These autoreactive cells make up 5% of the peripheral CD4 T cells, providing and estimate of the minimal frequency of positively selected cells that must subsequently undergo negative selection for self-tolerance to be preserved. Thus positive and negative selection occur in anatomically distinct sites.

Isolation of a new superantigen with potent mitogenic activity to murine T cells from Streptococcus pyogenes

A mitogenic substance on murine lymphocytes was detected in the culture supernate of Streptococcus pyogenes type 12 strain. This substance had a molecular weight of 28,000 and pI 9.2, and was designated as S. pyogenes mitogen (SPM). The proliferative response of C3H/HeN spleen cells began at 1 ng ml-1 and reached a maximal response at 100 ng ml-1 of SPM for 4 days culture. Anti-Thy 1.2 mAb and complement-treated spleen cells abrogated the proliferative response to any dose of SPM. Although the anti-major histocompatibility complex class 1 mAbs had no blocking effect on proliferation by SPM, this proliferation was substantially inhibited by the addition of either anti-I-A or anti-I-E mAb, and complete inhibition was produced by the addition of both mAbs. Fixed antigen-presenting cells still induced T cell proliferation by SPM. A significant expansion of T cells bearing V beta 13 T-cell receptor was observed up to 73% among the Thy 1.2+ cells in cultures stimulated with SPM, indicating expansion in a V beta-specific manner. Immunoblotting of IEF-separated proteins showed that anti-streptococcal pyrogenic exotoxin (SPE) C reacted with a protein of pI 6.9 and anti-SPEB did not show any reactivity. SPEA was reported to expand V beta 8.1 and 8.2 bearing murine T cells, and SPM did not. SPM also exhibited potent mitogenic activity on human T cells and V beta 21+ T cells were selectively expanded. These results lead to the conclusion that SPM was neither SPEA, B nor C, but a new protein belonging to a group of streptococcal superantigens with activity on not only human but also murine lymphocytes.

Potentiation of inhaled staphylococcal enterotoxin B-induced toxicity by lipopolysaccharide in mice

Nonhuman primates are the established model for evaluating toxic responses to staphylococcal enterotoxins (SEs), as they react similarly to humans. Rodents are generally considered unresponsive to SEs. Binding affinities and T-cell reactivity suggest that SE binds more efficiently to primate major histocompatability complex class II receptors than to mouse receptors. We investigated the potentiation of staphylococcal enterotoxin B (SEB) inhalation toxicity by lipopolysaccharide (LPS) in BALB/c mice. Lethality occurred only when SEB was potentiated by LPS. Neither SEB nor LPS produced lethal effects alone. Temporal responses of interleukin 1 alpha, tumor necrosis factor alpha, interleukin 2, and interferon-gamma evoked by inhaled SEB were enhanced by LPS. By 24 hr after intoxication, serum cytokines decreased to baseline levels, and consistent pulmonary perivascular leukocytic infiltrates were evident histologically. Histologic lesions induced by inhalation exposure to SEB by mice, with or without potentiation by LPS, were similar to those in the rhesus monkey. Predominant pulmonary lesions included severe, diffuse interstitial and alveolar pulmonary edema, leukocytic infiltrates, mild perivascular edema, and alveolar fibrin deposition. Although the mechanism of aerosolized SEB-induced toxicity has not been completely resolved, similarities in histologic lesions, cytokine responses, and acute dose-response suggest the LPS-potentiated mouse model may be a credible alternative to the nonhuman primate model.

Function of the p55 tumor necrosis factor receptor "death domain" mediated by phosphatidylcholine-specific phospholipase C

Tumor necrosis factor (TNF) is a pleiotropic mediator of inflammation that has been implicated in the pathogenesis of devastating clinical syndromes including septic shock. We have investigated the role of a TNF-responsive phosphatidylcholine-specific phospholipase C (PC-PLC) for the cytotoxic and proinflammatory activity of TNF. We show here that the cytotoxicity signaled for by the so-called "death domain" of the p55 TNF receptor is associated with the activation of PC-PLC. The xanthogenate tricyclodecan-9-yl (D609), a specific and selective inhibitor of PC-PLC, blocked the cytotoxic action of TNF on L929 and Wehi164 cells. In vivo, D609 prevented both adhesion molecule expression in the pulmonary vasculature and the accompanying leukocyte infiltration in TNF-treated mice. More strikingly, D609 protects BALB/c mice from lethal shock induced either by TNF, lipopolysaccharide, or staphylococcal enterotoxin B. Together these findings imply PC-PLC as an important mediator of the pathogenic action of TNF, suggesting that PC-PLC may serve as a novel target for anti-inflammatory TNF antagonists.

Activation by mitogens and superantigens of axolotl lymphocytes: functional characterization and ontogenic study

Urodele amphibians have weak and slow immune responses compared to mammals and anuran amphibians. Using new culture conditions, we tested the ability of lymphocytes of a well-studied salamander, the Mexican axolotl (Ambystoma mexicanum) to proliferate in vitro with diverse mitogenic agents. We demonstrated that the axolotl has a population of B lymphocytes that proliferate specifically and with a high stimulation index to the lipopolysaccharide (LPS) known as a B-cell mitogen in mammals. This proliferative capacity is observed without significant changes throughout ontogenesis. In the presence of LPS, axolotl B lymphocytes are able to synthesize and secrete both isotopes of immunoglobulin described in this species, IgM and IgY. Moreover, a distinct lymphocyte subpopulation is able to poliferate significantly in response to the mitogens usually known as T-cell specific in mammals, phytohaemagglutinin (PHA) and concanavalin A (Con A). The activated cells are T lymphocytes, as shown by depletion experiments performed in vitro with monoclonal antibodies, and in vivo by thymectomy. Splenic T lymphocytes of young axolotls (before 10 months) do not have this functional ability, which suggests maturation and/or migration phenomena during T-cell ontogenesis in this species. Axolotl lymphocytes are able to proliferate in vitro with a significant stimulation index to staphylococcal enterotoxins A and B (SEA and SEB). These products act on mammalian lymphocytes as superantigens: in combination with products of the major histocompatibility complex (MHC), they bind T-cell receptors with particular V beta elements. The fact that these superantigens are able to activate lymphocytes of a primitive vertebrate suggests a striking conservation of molecular structures implied in superantigen presentation and recognition.