Self-tolerance and autoimmunity

COVID-19 as a trigger of Guillain-Barré syndrome: A review of the molecular mechanism

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a pandemic with serious complications. After coronavirus disease 2019 (COVID-19), several post-acute COVID-19 syndromes (PACSs) and long-COVID sequels were reported. PACSs involve many organs, including the nervous, gustatory, and immune systems. One of the PACSs after SARS-CoV-2 infection and vaccination is Guillain-Barré syndrome (GBS). The incidence rate of GBS after SARS-CoV-2 infection or vaccination is low. However, the high prevalence of COVID-19 and severe complications of GBS, for example, autonomic dysfunction and respiratory failure, highlight the importance of post-COVID-19 GBS. It is while patients with simultaneous COVID-19 and GBS seem to have higher admission rates to the intensive care unit, and demyelination is more aggressive in post-COVID-19 GBS patients. SARS-CoV-2 can trigger GBS via several pathways like direct neurotropism and neurovirulence, microvascular dysfunction and oxidative stress, immune system disruption, molecular mimicry, and autoantibody production. Although there are few molecular studies on the molecular and cellular mechanisms of GBS occurrence after SARS-CoV-2 infection and vaccination, we aimed to discuss the possible pathomechanism of post-COVID-19 GBS by gathering the most recent molecular evidence.

Prospects for the potential of RNA interference in the treatment of autoimmune diseases: Small interfering RNAs in the spotlight

The identification of RNA interference (RNAi) has caused a growing interest in harnessing its potential in the treatment of different diseases. Modulation of dysregulated genes through targeting by RNAi represents a potential approach with which to alter the biological pathways at a post-transcriptional level, especially as it pertains to autoimmunity and malignancy. Short hairpin RNAs (shRNA), short interfering RNAs (siRNA), and microRNAs (miRNA) are mainly involved as effector mechanisms in the targeting of RNAi biological pathways. The manipulation and delivery of these molecules in an efficient way promotes the specificity and stability of RNAi-based systems, while minimizing the unwanted adverse reactions by the immune system and reducing cytotoxicity and off-target effects. Advances made to date in identifying the etiopathogenesis of autoimmune diseases has prompted the utilization of RNAi-based systems in vitro and in vivo. Future investigations aimed at deciphering the molecular basis of RNAi and optimizing the delivery of RNAi-based targeting systems will hopefully promote the applicability of such regulatory mechanisms and, ultimately, transfer the acquired knowledge from bench-to-bedside to ameliorate human diseases. In this review, we seek to clarify the potential of RNAi, with a focus on siRNAs, in designing therapeutics for potential treatment of human autoimmune disorders.

CRISPR: a new principle of genome engineering linked to conceptual shifts in evolutionary biology

The CRISPR-Cas systems of bacterial and archaeal adaptive immunity have become a household name among biologists and even the general public thanks to the unprecedented success of the new generation of genome editing tools utilizing Cas proteins. However, the fundamental biological features of CRISPR-Cas are of no lesser interest and have major impacts on our understanding of the evolution of antivirus defense, host-parasite coevolution, self versus non-self discrimination and mechanisms of adaptation. CRISPR-Cas systems present the best known case in point for Lamarckian evolution, i.e. generation of heritable, adaptive genomic changes in response to encounters with external factors, in this case, foreign nucleic acids. CRISPR-Cas systems employ multiple mechanisms of self versus non-self discrimination but, as is the case with immune systems in general, are nevertheless costly because autoimmunity cannot be eliminated completely. In addition to the autoimmunity, the fitness cost of CRISPR-Cas systems appears to be determined by their inhibitory effect on horizontal gene transfer, curtailing evolutionary innovation. Hence the dynamic evolution of CRISPR-Cas loci that are frequently lost and (re)acquired by archaea and bacteria. Another fundamental biological feature of CRISPR-Cas is its intimate connection with programmed cell death and dormancy induction in microbes. In this and, possibly, other immune systems, active immune response appears to be coupled to a different form of defense, namely, "altruistic" shutdown of cellular functions resulting in protection of neighboring cells. Finally, analysis of the evolutionary connections of Cas proteins reveals multiple contributions of mobile genetic elements (MGE) to the origin of various components of CRISPR-Cas systems, furthermore, different biological systems that function by genome manipulation appear to have evolved convergently from unrelated MGE. The shared features of adaptive defense systems and MGE, namely the ability to recognize and cleave unique sites in genomes, make them ideal candidates for genome editing and engineering tools.

Restoring self-tolerance in autoimmune diseases by enhancing regulatory T-cells

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

Curcumin and autoimmune disease

The immune system has evolved to protect the host from microbial infection; nevertheless, a breakdown in the immune system often results in infection, cancer, and autoimmune diseases. Multiple sclerosis, rheumatoid arthritis, type 1 diabetes, inflammatory bowel disease, myocarditis, thyroiditis, uveitis, systemic lupus erythromatosis, and myasthenia gravis are organ-specific autoimmune diseases that afflict more than 5% of the population worldwide. Although the etiology is not known and a cure is still wanting, the use of herbal and dietary supplements is on the rise in patients with autoimmune diseases, mainly because they are effective, inexpensive, and relatively safe. Curcumin is a polyphenolic compound isolated from the rhizome of the plant Curcuma longa that has traditionally been used for pain and wound-healing. Recent studies have shown that curcumin ameliorates multiple sclerosis, rheumatoid arthritis, psoriasis, and inflammatory bowel disease in human or animal models. Curcumin inhibits these autoimmune diseases by regulating inflammatory cytokines such as IL-1beta, IL-6, IL-12, TNF-alpha and IFN-gamma and associated JAK-STAT, AP-1, and NF-kappaB signaling pathways in immune cells. Although the beneficial effects of nutraceuticals are traditionally achieved through dietary consumption at low levels for long periods of time, the use of purified active compounds such as curcumin at higher doses for therapeutic purposes needs extreme caution. A precise understanding of effective dose, safe regiment, and mechanism of action is required for the use of curcumin in the treatment of human autoimmune diseases.

Periodontal manifestations of collagen vascular disorders

Chronic degeneration of connective tissue components can be produced by a variety of autoimmune mechanisms. The designations connective tissue disease and collagen-vascular disease are commonly used to describe such conditions when a patient exhibits chronic, immune-mediated deterioration of connective tissue structures in a systemic distribution. Recognized conditions that fit this definition include rheumatoid arthritis, lupus erythematosus, progressive systemic sclerosis, CREST syndrome, and mixed connective tissue disease. Several characteristic oral manifestations of these conditions are recognized. Xerostomia associated with any of these conditions in addition to dryness of the eyes is the definition of secondary Sjögren's syndrome. Fibrosis of facial skin and the resulting limited jaw opening are diagnostic features of progressive systemic sclerosis. Several periodontal manifestations are associated with these connective tissue disorders. Dramatic periodontal ligament space widening that is associated with some cases of progressive systemic sclerosis has been appreciated for more than five decades. However, it has been more recently reported that the majority of progressive systemic sclerosis patients exhibit at least subtle generalized periodontal ligament widening when intraoral radiographs are carefully evaluated. This finding is, however, of limited periodontal significance because the teeth are typically not mobile. Comparisons of periodontitis indices such as pocket depth between healthy subjects and patients with progressive systemic sclerosis do not reveal significant differences (21). In addition, recent evidence suggests a tendency for more severe or progressive manifestations of periodontitis as a consequence of xerostomia that may result from these diseases.

Treatment of an autoimmune disease with "classical" T cell veto: a proposal

Immune responses protect against infectious diseases and cancers. In normal circumstances, the immune system is tolerant to self. However, under certain conditions this tolerance is broken. The immune system attacks otherwise normal tissue. An autoimmune disease ensues. Strategies are now being sought that remove the pathogenic T cells without affecting other immune functions. "Classical" veto has been described as an immune suppressive mechanism able to remove T cells in a highly specific and effective manner. The present article briefly reviews the current knowledge on the development of autoreactive T cells and their regulation in the periphery. It describes "classical" veto, its mechanisms, and its novel applications. Finally, it argues that "classical" veto can be adapted to treat an autoimmune disease, such as type I diabetes mellitus.

Experimental Goodpasture's syndrome in Wistar-Kyoto rats immunized with alpha3 chain of type IV collagen

BACKGROUND

Glomerulonephritis and lung hemorrhage of autoimmune Goodpasture syndrome develop due to immune reactions against epitope(s) of the non-collagenous (NC1) domain of alpha3-chain of type IV collagen [alpha3(IV) NC1]. Whether thymic mechanisms have a role in the loss of tolerance to the Goodpasture epitope has not been established. We studied the renal and pulmonary effects of immunization with different forms (monomer, dimer, or hexamer) of alpha3(IV) NC1 collagen in Wistar-Kyoto (WKY) rats, and assessed whether the intrathymic inoculation of the antigen may protect against anti-GBM disease.

METHODS

WKY rats were immunized with bovine alpha3(IV) monomer, dimer, or hexamer, or with alpha3(IV) NC1 synthetic peptide. Renal function, kidney and lung immunohistology, and circulating and tissue bound antibodies to type IV collagen chains were analyzed. Effects of intrathymic inoculation of antigen on subsequent disease induction were analyzed in WKY rats given alpha3(IV) NC1 dimer or GBM preparation intrathymically 48 hours before immunization.

RESULTS

Proteinuria, linear IgG deposition in GBM, and crescentic glomerulonephritis developed in WKY rats immunized with alpha3(IV) NC1 dimer or hexamer. Lesions were dose-dependent upon injections of 10 to 100 microgram dimer. The alpha3(IV) NC1 monomer induced less severe proteinuria and no crescents. Pulmonary hemorrhage was detectable in 35% of rats immunized with 25 to 100 microgram alpha3(IV) NC1 dimer; alpha3(IV) synthetic peptide (36 carboxyl terminal) did not induce disease. Rats injected intrathymically with up to 100 microgram alpha3(IV) NC1 dimer or with GBM 48 hours before immunization were not protected against subsequent development of proteinuria and glomerulonephritis.

CONCLUSIONS

These findings document that glomerulonephritis and lung hemorrhage can be elicited in WKY rats by immunization with alpha3(IV) NC1. Failure of the intrathymic inoculation of antigen to prevent disease suggests that immunological tolerance cannot be achieved by this intervention, in contrast to other autoimmune conditions, and may imply independent roles for cellular and humoral nephritogenic pathways in anti-GBM nephritis.

Significantly increased occurrence of HLA-DQB1*0301 allele in patients with ocular cicatricial pemphigoid

To determine the immunogenetic characteristics of patients with immune-mediated subepithelial blistering diseases of mucous membranes, we performed HLA-typing for the class II MHC gene DQB1*0301 allele using a direct method. Genomic DNA extracted from Caucasian patients was amplified by polymerase chain reaction using primer pairs specific for the DQB loci followed by Southern blotting with a peroxidase-conjugated sequence-specific oligonucleotide probe. Seventy-six percent (16/21) of patients with ocular mucosal disease (with or without oral mucosal and skin diseases) carried the DQB1*0301 allele; by contrast, only 33% (14/42) of race-, age-, and geography-matched normal individuals carried the DQB1*0301 allele (p < 0.005). The relative risk for ocular disease if DQB1*0301 allele is present is 6.4, similar to the relative risk of 8 for patients with ocular but no oral disease (pure ocular cicatricial pemphigoid, p < 0.025). In patients with oral mucosal disease (with or without ocular mucosal and skin diseases), 68% (15/22) carried the DQB1*0301 allele (p < 0.025). When patients with ocular disease were excluded, however, the increased occurrence of the DQB1*0301 allele in patients with oral disease was not statistically significant (64%, 7/11, p < 0.25). In patients with subepidermal blistering skin disease but no oral or ocular disease, there was no increase in the occurrence of the DQB1*0301 allele (38%, 5/13, p > 0.5). The significantly increased occurrence of the DQB1*0301 allele in patients with ocular mucosal disease may point to a distinct immunogenetic factor that predisposes patients to develop an ocular scarring process.

Molecular, metabolic and immune evidence suggest that systemic autoimmune disease is antigen-mediated

Patients with systemic lupus erythematosus generate a sustained immune response against self. The tools of modern molecular biology have been applied to cell activities and elements/signals of the immune system, but a structural or regulatory defect has not been found. When deoxyribonucleic acids for autoantibodies were cloned and sequenced, they were like other autoantibody DNA sequences; when genetic materials for autoantibodies were inserted into transgenic mice, cells secreting the antibodies were subject to normal control mechanisms and eliminated. A failure to clear self-reactive antibody producing thymocytes has not been demonstrated in human systemic lupus erythematosus. Molecular analyses of the efferent side of the immune response have been largely normal in systemic lupus erythematosus. The structure of autoantibodies suggests that they have been generated by selection pressures and the presence of endogenous antigens. If the immune system attack on self was secondary, structural changes and metabolic reactions capable of generating antigens should be found in systemic lupus erythematosus cells. Structural changes have been found in deoxyribonucleic acid from phytohaemagglutinin-stimulated systemic lupus erythematosus lymphocytes in the form of S1 nuclease-sensitive deoxyribonucleic acid breaks. Altered cellular macromolecules could result from endogenous metabolic processes, particularly oxygen free radicals and arachidonic acid metabolites. Excess free-radical species, generating positive nitroblue tetrazolium-reacting material and positive chemiluminescence, have been found in most but not all phytohaemagglutinin-stimulated lupus lymphocyte samples. If endogenous metabolic processes act on endogenous deoxyribonucleic acid, endogenous cell DNA breakdown may lead to low molecular weight deoxyribonucleic acids and deoxyribonucleic acid/immune complexes in systemic lupus erythematosus sera that are potentially immunogenic. These combined findings suggest that the exaggerated immune responses of systemic lupus erythematosus may be a normal response to protect the host from a perceived antigenic threat.

Transplantation tolerance: fooling mother nature

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T-cell receptor expression in C57BL/6 mice that reject or are rendered tolerant to bm1 cardiac grafts

To study the molecular immunologic features of allograft rejection and tolerance induction by intrathymic pretreatment we developed a murine model of cardiac transplantation. In this model the transplant recipient was the C57BL/6 mouse with its major histocompatibility phenotype H-2b. Donors of cells for intrathymic pretreatment and of hearts for grafting were mice of the bm1 mutation. The bm1 mutation involves substitution of three amino acids in one of the alpha helixes of the class I H-2Kb molecule. Because of the discrete molecular configuration of the transplant antigen we hypothesized that there would be limited heterogeneity of receptor expression on C57BL/6 T cells responding to bm1 cardiac grafts and that intrathymic pretreatment would alter the T-cell repertoire of graft recipients by causing elimination of T cells responsible for graft rejection. Mice were given 0.3 ml of antilymphocyte serum intraperitoneally and had intrathymic injection of 25 x 10(6) bm1 splenocytes 12 to 21 days before transplantation with a bm1 cardiac graft. Flow cytometric analysis of lymph node and spleen cells was used to study the V beta T-cell repertoire of graft recipients. Cells were stained with monoclonal antibodies to CD3 and 13 V beta regions (n = 5, each group) of T cells in naive, sensitized, and tolerant animals. Untreated C57BL/6 mice (n = 9) rejected bm1 cardiac grafts a mean of 20.4 days after transplantation. Twelve mice pretreated with antilymphocyte serum and intrathymic bm1 cells had permanent graft survival (> 100 days, p < 0.0001). Animals treated with antilymphocyte serum alone (n = 5) or pretreated animals undergoing third-party BALB/c grafts (n = 4) rejected grafts in the normal time frame. There was significant alteration of percentage receptor expression of V beta 5.1, 7, 12, 13, and 17a in sensitized and tolerant mice. Of interest, V beta 7 expression was increased in the sensitized mice (3.8% to 8.3%,p = 0.005) and was virtually eliminated in tolerant mice (p = 0.005). In conclusion, these data suggest that V beta 7 is a critical receptor in the C57BL/6 response to subcutaneous bm1 cardiac grafts. Pretreatment of graft recipients with one dose of antilymphocyte serum and intrathymic bm1 cells appears to produce permanent tolerance to bm1 grafts with elimination of T cells expressing receptor chain V beta 7.

The effect of silicone-gel on the immune response

Silicone materials have been used in medical applications for at least 30 years. Despite this long history of use the question whether silicones can mediate an immunological reaction that may be detrimental to the host remains unanswered. Most studies on the biocompatability of silicones conclude that silicones are chemically stable compounds, which however are often capable of eliciting a benign chronic inflammatory response. Recently, our laboratory has conducted a series of animal experiments aimed at determining the immunological adjuvancy potential of silicone-gel taken from commercial breast implants. Our previous studies have indicated that silicone-gel is a potent humoral (antibody) adjuvant. Our present studies have found that silicone-gel is capable of eliciting auto-antibodies to rat thyroglobulin and bovine collagen II. However this immune response did not produce any histological evidence of thyroiditis or arthritis. Theories to explain why silicone-gel behaves as an adjuvant are discussed along with discussion of the hypothesis on the desirability of replacing silicone-gel with a more hydrophilic material in bioimplants.

Divergent evolution may link human immunodeficiency virus GP41 to human CD4

A local sequence similarity of HIV envelope proteins (gp120 and gp41) to immunoglobulins suggests that a mimicry phenomenon may form the basis of the HIV-cell membrane interaction and of HIV-induced autoimmune reaction. We explored the hypothesis of any deeper relationship between HIV env proteins and immunoglobulin family members. An overall DNA sequence similarity between gp41 coding region of env gene and the HIV-receptor CD4 gene was observed and a 14-base-long oligonucleotide, almost unique in the GenBank, was found in gp41 and CD4 genes. The alignment of env gene to CD4 gene and to 84 different sequences showed a significantly higher homology score and a nonrandom similarity in the CD4-env alignment. A significant similarity was also found between the env protein and the sequence encoded by an alternate reading frame of CD4 gene. Our observations suggest that gp41 coding region might have a different origin than the gp120 coding region of the env gene, and that a divergent evolution might link gp41 to CD4 or immunoglobulin family members. In this study the analysis of alternate-reading-frame products is also proposed as a novel approach to investigate evolutionary links and structure-function relationships.

Structural aspects of recognition motifs contributing to autoimmune responses

Sequence analysis of autoimmune-associated antibodies has suggested a structural relatedness between genes used to encode autoantibodies and those encoding unrelated antibodies without autoreactive specificities. Subsequently, the basis for cross-reactive idiotypes across germ-line lineages, as well as conserved interspecies cross-reactivities of autoantigens among serologically similar antibodies, may result from evolutionary duplication of particular types of recognition motifs. As a first step toward elucidating structural recognition principles underlying possible cross-reactive epitopes involved in autoimmune pathologies, structural features of selected motifs associated with native ligand binding are examined for their inherent occurrence in antibody and T-cell receptor repertoires. This analysis considers the putative recognition features representative of common motif subsets shared with loop structures in CDR2 and FR3 regions of antibodies such as charge-2x-charge-x-charge or hydrogen bond donor (acceptor)-2x-charge-x-hydrogen bond donor (acceptor) type motifs, where x is any residue that can participate in maintaining a loop conformation. Such tracts encoded in the CRD2 and FR3 regions of heavy chains of antibodies and T-cell receptors (TCRs) associated with autoimmune dysfunction, with non-autoreactive antibodies, and with native host proteins. Such evolutionarily conserved motifs may be targets for complementary interactions involving autoantibodies and receptors.

Autoimmunity, polyclonal B-cell activation and infection

It is widely believed that autoimmunity is an integral part of the immune system, and that genetic, immunologic, hormonal, environmental and other factors contribute to the pathogenesis of autoimmune disease. Thus, autoimmune disease may represent an abnormal expression of immune functions instead of loss of tolerance to self, and it can be organ specific or systemic in its manifestations. We review the various factors that contribute to the development of autoimmune disease; we also review the mechanisms of polyclonal B-cell activation, with emphasis on the role of infectious agents. We consider systemic lupus erythematosus in humans and in experimental animals as prototypic autoimmune disease, and we summarize data to indicate that polyclonal B-cell activation is central to the pathogenesis of systemic autoimmune disease. The effect of polyclonal B-cell activation, brought about by injections of a B-cell activator-lipopolysaccharide from Gram-negative bacteria-is sufficient to cause autoimmune disease in an immunologically normal host. In fact, autoimmune disease can be arrested if excessive polyclonal B-cell activation is suppressed; alternatively, autoimmune disease can be exacerbated if polyclonal B-cell activation is enhanced. We explore the mechanism of tissue injury when autoimmune disease is induced or exacerbated, and we consider the pathogenic roles of autoantibodies, immune complexes, complement, the blood cell carrier system, and the mononuclear phagocyte system. Although polyclonal B-cell activation may be the mechanism whereby various factors can cause or exacerbate systemic autoimmune disease, polyclonal B-cell activation may cause autoimmune disease on its own.

Autoimmunity to glutamic acid decarboxylase (GAD) in Stiff-Man syndrome and insulin-dependent diabetes mellitus

Stiff-Man syndrome (SMS) is a disorder of the CNS, characterized by rigidity of the body musculature, which has been hypothesized to result from an impairment of GABAergic neurotransmission. GABA is the main inhibitory neurotransmitter of the brain. It is also a putative signal molecule in the pancreas, where it is produced by beta cells (insulin-secreting cells)--the autoimmune target in insulin-dependent diabetes mellitus (IDDM). Autoantibodies to the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) have been found in SMS and in IDDM. This review summarizes evidence suggesting that SMS may be an autoimmune disease and discusses the possible significance of the autoimmune response to GAD in SMS and IDDM.