MICROBIAL SUPERANTIGENS AS ETIOPATHOGENIC AGENTS IN AUTOIMMUNITY

Superantigen influence in conjunction with cytokine polymorphism potentiates autoimmunity in systemic lupus erythematosus patients

Risk posed by microbial superantigens in triggering or exacerbating SLE in genetically predisposed individuals, thereby altering the response to its treatment strategies, has not been studied. Using streptococcal pyrogenic exotoxin A and staphylococcal enterotoxin B as prototype superantigens, we have demonstrated that they profoundly affect the magnitude of polyclonal T cell response, particularly CD4(+) T cells and expression of CD45RA and CD45RO, and cytokine secretion in vitro in SLE patient PBMCs. Also, reduced proportions of FoxP3 expressing CD4(+)CD25(+) T cells were detected in SLE as compared to healthy control PBMCs. Furthermore, polymorphism in IL-10 and TGF-β showed significant association with SLE in our study population. These results indicate that accumulation of superantigen-reactive T cells and cytokine polymorphism may cause disease exacerbation, relapse, or therapeutic resistance in SLE patients. Attempts to contain colonizing and/or superantigen-producing microbial agents in SLE patients in addition to careful monitoring of their therapy may be worthwhile in decreasing disease severity or preventing frequent relapses. The study suggests that superantigen interference in conjunction with cytokine polymorphism may play a role in immune dysregulation, thereby contributing to autoimmunity in SLE. Therefore, changes in T cell phenotypes and cytokine secretion might be good indicators of therapeutic efficacy in these patients.

Staphylococcal enterotoxins in the etiopathogenesis of mucosal autoimmunity within the gastrointestinal tract

The staphylococcal enterotoxins (SEs) are the products of Staphylococcus aureus and are recognized as the causative agents of classical food poisoning in humans following the consumption of contaminated food. While illness evoked by ingestion of the SE or its producer organism in tainted food are often self-limited, our current understanding regarding the evolution of S. aureus provokes the utmost concern. The organism and its associated toxins, has been implicated in a wide variety of disease states including infections of the skin, heart, sinuses, inflammatory gastrointestinal disease, toxic shock, and Sudden Infant Death Syndrome. The intricate relationship between the various subsets of immunocompetent T cells and accessory cells and the ingested material found within the gastrointestinal tract present daunting challenges to the maintenance of immunologic homeostasis. Dysregulation of the intricate balances within this environment has the potential for extreme consequences within the host, some of which are long-lived. The focus of this review is to evaluate the relevance of staphylococcal enterotoxin in the context of mucosal immunity, and the underlying mechanisms that contribute to the pathogenesis of gastrointestinal autoimmune disease.

Peripheral CD25 positive T lymphocytes with biased T cell receptor Vbeta gene usage in autoimmune endogenous posterior uveitis

Aims-To determine T cell receptor (TCR) Vbeta gene usage in peripheral blood T lymphocytes of patients with endogenous posterior uveitis (EPU). If biased TCR variable (V) gene usage occurs in this autoimmune disease, it should be detectable in immune activated peripheral blood T cells in vivo.Methods-Relative proportions of each Vbeta gene family expressed in total peripheral blood lymphocytes (PBL) and in vivo activated (CD25+) T cells from patients with EPU and controls were determined using the anchored polymerase chain reaction (anchored PCR) in conjunction with a novel hybridisation assay. The TCR Vbeta repertoires seen in these cell populations were then compared.Results-Vbeta1 usage within the CD25+ lymphocytes of patients with EPU was substantially elevated (mean +/- SD 15 +/-9%) compared with control CD25+ cells (3.3 +/-2.4%).Conclusions-By contrasting the repertoires of these cell populations, biased TCR Vbeta gene usage was detected in patients with EPU, namely increased usage of Vbeta1 in CD25+ T cells from peripheral blood of these patients. This approach of directly analysing the activated T cells in blood, using bulk PBL as an internal control, has wide applicability where specific T cell subpopulations are thought to play an important aetiopathological role.

CNS immune responses following experimental stroke

BACKGROUND AND PURPOSE

Animals subjected to an inflammatory insult with lipopolysaccharide (LPS) at the time of stroke are predisposed to develop a detrimental autoimmune response to myelin basic protein (MBP). In this study, we sought to determine whether other inflammatory stimuli could similarly invoke central nervous system (CNS) autoimmunity and whether these detrimental autoimmune responses occurred to antigens other than MBP.

METHODS

Male Lewis rats underwent 3 h middle cerebral artery occlusion (MCAO) and received intraperitoneal injections of LPS, staphylococcal enterotoxin B (SEB), lipoteichoic acid (LTA) or saline at the time of reperfusion. Behavioral tests were performed at set time intervals after MCAO and animals were sacrificed at 1 month to analyze the immune response to MBP, neuron specific enolase (NSE) and proteolipid protein (PLP).

RESULTS

Lymphocytes from SEB treated animals were highly reactive to all tested CNS antigens, but treatment with LPS was most likely to lead to a TH: 1(+) response. A TH: 1(+) response to MBP, NSE or PLP in spleen was associated with worse outcome, although the response to NSE was most predictive of poor outcome. Animals with a cell mediated autoimmune response to either MBP or NSE in spleen had a concomitant humoral response to these antigens.

CONCLUSIONS

These data show that LPS, but not other inflammatory stimuli, increase the likelihood of developing a detrimental autoimmune response to an array of brain antigens.

Structure-based preliminary analysis of immunity and virulence of SARS coronavirus

The research on SARS-associated coronavirus (SARS-CoV) has not stopped since its discovery, but the pathogenesis of SARS is still unclear. To explore the possible molecular mechanisms of the invasion and virulence of SARS-CoV, we investigated the structural basis of the viral proteins using computational biology. Forty-five motifs relating to superantigens, toxins and other bioactive molecules were detected in the proteins of SARS-CoV. The results showed that the distribution of the motifs varied in different proteins. Enzyme-like motifs were located in the R protein, while ICAM- 1-like and toxin-like molecules were located in the spike, envelop, nucleocapsid, PUP1, PUP 2 and PUP 4 proteins. Comparison of SARS-CoV with other viruses (OC43, PEDV, HRSV, HHerpV and HAdenoV) showed that each group of motifs was different for each type of virus. Data suggest that the proteins of SARS-CoV with toxic motifs might play crucial roles in targeting host cells and interfering with the immune system. This study provides new information for drug and vaccine design, as well as therapeutic strategies against SARS.

Superantigens: structure-function relationships

Superantigens are a class of highly potent immuno-stimulatory molecules produced by Staphylococcus aureus and Streptococcus pyogenes. These toxins possess the unique ability to interact simultaneously with MHC class II molecules and T-cell receptors, forming a trimolecular complex that induces profound T-cell proliferation. The resultant massive cytokine release causes epithelial damage and leads to capillary leak and hypotension. The staphylococcal superantigens are designated staphylococcal enterotoxins A, B, C (and antigenic variants), D, E, and the recently discovered enterotoxins G to Q, and toxic shock syndrome toxin-1. The streptococcal superantigens include the pyrogenic exotoxins A (and antigenic variants), C, G-J, SMEZ, and SSA. Superantigens are implicated in several diseases including toxic shock syndrome, scarlet fever and food poisoning; and their function appears primarily to debilitate the host sufficiently to permit the causation of disease. Structural studies over the last 10 years have provided a great deal of information regarding the complex interactions of these molecules with their receptors. This, combined with the wealth of new information from genomics initiatives, have shown that, despite their common molecular architecture, superantigens are able to crosslink MHC class II molecules and T-cell receptors by a variety of subtly different ways through the use of various structural regions within each toxin.

Antinuclear antibody seropositivity in patients with cutaneous T-cell lymphoma

BACKGROUND

We attempted to determine the frequency and clinical relevance of antinuclear antibody (ANA) testing and positive ANA test results in patients with cutaneous T-cell lymphoma (CTCL).

METHODS

A retrospective chart and computer record review was conducted to determine the frequency of ANA testing in CTCL patients and the rate of seropositivity. Patients with a positive ANA were further examined to define possible explanations of the positive test.

RESULTS

Of 381 patients with CTCL, 66 (17%) had ANA tests; 8 of these (12.1%) were found to have an ANA titer greater than or equal to 1:40. Of patients with a positive ANA test, one was found to have chronic cutaneous lupus erythematosus histologically and clinically mimicking CTCL. Others were found to have a comorbid connective tissue disorder, some had apparent drug-induced antinuclear antibodies, and some had no identifiable reason for a positive ANA test.

CONCLUSION

ANA seropositivity does not appear to be increased in CTCL patients, and the ANA test remains a useful screening tool for differentiating between CTCL and connective tissue disorders.

In vitro assay of Staphylococcus aureus enterotoxin A activity in food

Staphylococcus aureus enterotoxin A (SEA) is a leading cause of food poisoning. The current test for functional activity of SEA requires monkeys or kittens. The major drawbacks of animal assays are lack of quantitation, poor reproducibility, low sensitivity, and high cost. In this report we describe and evaluate an alternative assay using T-cell proliferation to measure SEA activity in food. Human and rat lymphocytes proliferate in response to concentrations of SEA as low as 1 pg/ml, well below the pathogenic dose of 100 ng. This proliferation assay is highly sensitive, quantitative, and simple. Nonradioactive assays of T-cell proliferation were also suitable for detecting and measuring SEA, although with a 10-fold lower sensitivity. To evaluate the utility of this assay for food testing, four different food samples were mixed with SEA. In each sample, SEA was detected at a concentration of 1 ng/ml. Heat-inactivated SEA produced no detectable proliferation. These results demonstrate that an in vitro cell proliferation assay is an advantageous alternative to existing animal assays for measuring SEA activity in food.

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.

Experimental autoimmune uveitis: molecular mimicry and oral tolerance

Intraocular inflammatory disease or uveitis, which affects the uveal tract and the retina of the eyes in human, is the major cause of visual impairment. Experimental autoimmune uveitis (EAU) is a T-cell-mediated autoimmune disease directed against retinal proteins and has been studied in several mammalian species including subhuman primates as a model for human posterior uveitis. Autoimmune responses provoked by molecular mimicry occur when the nonself and host determinants are similar enough to cross-react yet different enough to break immunological tolerance, and is one of the proposed mechanisms for induction of autoimmune diseases. Therapeutic immunomodulatory strategies have been used to induce antigen-specific peripheral immune tolerance in animal models of T-cell-mediated autoimmune diseases by oral administration of autoantigens. Oral tolerance leads to unique mechanisms of tissue and disease-specific immunosuppression, which would circumvent the immunotherapeutic problem of multiple target tissue autoreactivity. Several groups have investigated the effects of delivering autoantigens across gastric mucosal surfaces. This review briefly discusses molecular mimicry and the mechanism of induction of oral tolerance with respect to immunopathogenesis of T-cell-mediated autoimmune disease in general and EAU in particular.

Fas expression and apoptosis in human B cells

Mechanisms of B cell apoptosis are critical in reducing aberrant B cell proliferations such as those that arise in autoimmune disease and in B cell malignancies. The physiologic interaction of CD4+ helper T cells and B lymphocytes has been extensively studied over the past two decades. Although CD4+ T cells are considered primarily to offer positive costimulatory signals for B cell differentiation into active immunoglobulin-secreting cells, recent studies have shown that CD4+ T cells are crucial in downregulating the humoral immune response. In the course of cognate interaction between CD40 ligand (CD40L)-bearing CD4+ T cells and CD40-expressing germinal center B cells, CD40 ligation results in augmented Fas expression at the B cell surface. Like CD40L, Fas ligand is expressed on activated CD4+ Th1 cells and when bound to Fas receptor on the B cell surface, initiates an apoptotic signal in that cell. Thus, CD4+ T cells limit the growth of autologous germinal center B cells by first inducing Fas expression and then instigating a death signal via Fas ligand. In this work, we will consider these observations about CD4+ T-cell-induced, Fas-mediated B cell death in the context of other factors that affect apoptosis in B cells, normal and malignant.