Positive selection for autoimmunity

The cliff edge model of the evolution of schizophrenia: Mathematical, epidemiological, and genetic evidence

How has schizophrenia, a condition that significantly reduces an individual's evolutionary fitness, remained common across generations and cultures? Numerous theories about the evolution of schizophrenia have been proposed, most of which are not consistent with modern epidemiological and genetic evidence. Here, we briefly review this evidence and explore the cliff edge model of schizophrenia. It suggests that schizophrenia is the extreme manifestation of a polygenic trait or a combination of traits that, within a normal range of variation, confer cognitive, linguistic, and/or social advantages. Only beyond a certain threshold, these traits precipitate the onset of schizophrenia and reduce fitness. We provide the first mathematical model of this qualitative concept and show that it requires only very weak positive selection of the underlying trait(s) to explain today's schizophrenia prevalence. This prediction, along with expectations about the effect size of schizophrenia risk alleles, are surprisingly well matched by empirical evidence. The cliff edge model predicts a dynamic change of selection of risk alleles, which explains the contradictory findings of evolutionary genetic studies.

Drug-induced lupus

INTRODUCTION

Drug-induced lupus (DIL) refers to an idiosyncratic side effect of numerous, apparently unrelated, medications, in which symptoms overlap with those of systemic lupus erythematosus. DIL is reversible by discontinuation of the medication. The etiological mechanism underlying DIL is linked to the inherent susceptibility of the adaptive immune system to lapse into auto-reactivity.

AREAS COVERED

Clinical and laboratory features of DIL will be compared with those of idiopathic systemic lupus and with other types of drug reactions with overlapping features. Formerly commonly-used drugs conferred very high risk of developing DIL, although the probability of developing DIL has not been established with most lupus-inducing drugs. Pharmacological or physiochemical properties of the parent compounds are uninformative, but the importance of reactive drug metabolites in initiating autoimmunity will be discussed. As with most systemic autoimmune diseases, the pathogenesis of DIL is complex and obscure. The role of complement and human leukocyte allotypes as well as drug acetylator phenotype inform the underlying mechanism, and several of these non-mutually exclusive concepts will be described.

EXPERT OPINION

The pros and cons of proposed mechanisms for DIL will be discussed in the context of current understanding of autoimmunity and immune tolerance to self.

A genome-wide homozygosity association study identifies runs of homozygosity associated with rheumatoid arthritis in the human major histocompatibility complex

Rheumatoid arthritis (RA) is a chronic inflammatory disorder with a polygenic mode of inheritance. This study examined the hypothesis that runs of homozygosity (ROHs) play a recessive-acting role in the underlying RA genetic mechanism and identified RA-associated ROHs. Ours is the first genome-wide homozygosity association study for RA and characterized the ROH patterns associated with RA in the genomes of 2,000 RA patients and 3,000 normal controls of the Wellcome Trust Case Control Consortium. Genome scans consistently pinpointed two regions within the human major histocompatibility complex region containing RA-associated ROHs. The first region is from 32,451,664 bp to 32,846,093 bp (−log10(p)>22.6591). RA-susceptibility genes, such as HLA-DRB1, are contained in this region. The second region ranges from 32,933,485 bp to 33,585,118 bp (−log10(p)>8.3644) and contains other HLA-DPA1 and HLA-DPB1 genes. These two regions are physically close but are located in different blocks of linkage disequilibrium, and ∼40% of the RA patients' genomes carry these ROHs in the two regions. By analyzing homozygote intensities, an ROH that is anchored by the single nucleotide polymorphism rs2027852 and flanked by HLA-DRB6 and HLA-DRB1 was found associated with increased risk for RA. The presence of this risky ROH provides a 62% accuracy to predict RA disease status. An independent genomic dataset from 868 RA patients and 1,194 control subjects of the North American Rheumatoid Arthritis Consortium successfully validated the results obtained using the Wellcome Trust Case Control Consortium data. In conclusion, this genome-wide homozygosity association study provides an alternative to allelic association mapping for the identification of recessive variants responsible for RA. The identified RA-associated ROHs uncover recessive components and missing heritability associated with RA and other autoimmune diseases.

RETRACTED: Drug-induced lupus erythematosus

Drug-induced lupus is a syndrome which share symptoms and laboratory characteristics with idiopathic systemic lupus erythematosus (SLE). The terms drug-induced lupus (DIL) and drug-induced lupus erythematosus (DILE) are preferred, but other ones are also used-drug-related lupus, lupus-like syndrome and lupus erythematosus medicamentosus. The first case of DILE was reported in 1945 and associated with sulfadiazine. In 1953, it was reported that DILE was related to the use of hydralazine. More than 80 drugs have been associated with DILE. The average age of patients with DILE is nearly twice that of patients with idiopathic SLE. Approximately half the patients with drug-induced SLE are women, compared with 90% of patients with idiopathic SLE. Similarly to idiopathic lupus, DILE can be divided into systemic, sub-acute cutaneous and chronic cutaneous lupus. The syndrome is characterised by arthralgia, myalgia, pleurisy, rash and fever in association with antinuclear antibodies in the serum. The clinical and laboratory manifestations of drug-induced SLE are similar to those of idiopathic SLE, but central nervous system and renal involvement are rare in DILE. Recognition of DILE is important because it usually reverts within a few weeks after stopping the drug. This review discusses the general issues in DILE, such as pathogenic mechanisms, clinical forms and diagnostic criteria, and provides more detailed information for some of the most recent implicated drugs: minocycline, statins, anti-TNF-alpha agents.

T-helper cell intrinsic defects in lupus that break peripheral tolerance to nuclear autoantigens

Special populations of T helper cells drive B cells to produce IgG class switched, pathogenic autoantibodies in lupus. The major source of antigenic determinants (epitopes) that trigger interactions between lupus T and B cells is nucleosomes of apoptotic cells. These epitopes can be used for antigen-specific therapy of lupus. Secondly, the autoimmune T cells of lupus are sustained because they resist anergy and activation-induced programmed cell death by markedly upregulating cyclooxygenase (COX) 2 along with the antiapoptotic molecule c-FLIP. Only certain COX-2 inhibitors block pathogenic anti-DNA autoantibody production in lupus by causing death of autoimmune T helper cells. Hence COX-2 inhibitors may work independently of their ability to block the enzymatic function of COX-2, and structural peculiarities of these select inhibitors may lead to better drug discovery and design.

Drug-induced lupus erythematosus

Among the numerous idiopathic immune-mediated diseases that can be drug-induced, such as pemphigus, psoriasis, lichen, etc, drug-induced lupus is the most widely commented upon and investigated. The terms drug-induced lupus (DIL) and drug-induced lupus erythematosus (DILE) are preferred, but other ones are also used--drug-related lupus, lupus-like syndrome, and lupus erythematosus medicamentosus. This review discusses the general issues in DILE, such as pathogenic mechanisms, clinical forms, and diagnostic criteria, and provides more detailed information for some of the implicated drugs: minocycline, statins, terbinafine, etc.

The regulatory C-terminal determinants within mycobacterial heat shock protein 65 are cryptic and cross-reactive with the dominant self homologs: implications for the pathogenesis of autoimmune arthritis

The 65-kDa mycobacterial heat shock protein (Bhsp65) has been invoked in the pathogenesis of both adjuvant arthritis (AA) in the Lewis rat (RT.1(l)) and human rheumatoid arthritis. Arthritic Lewis rats in the late phase of AA show diversification of the T cell response to Bhsp65 C-terminal determinants (BCTD), and pretreatment of naive Lewis rats with a mixture of peptides representing these neoepitopes affords protection against AA. However, the fine specificity and physiologic significance of the BCTD-directed T cell repertoire, and the role of homologous self (rat) hsp65 (Rhsp65), if any, in spreading of the T cell response to Bhsp65 have not yet been examined. We observed that T cells primed by peptides comprising BCTD can adoptively transfer protection against AA to the recipient Lewis rats. However, these T cells can be activated by preprocessed (peptide) form of BCTD, but not native Bhsp65, showing that BCTD are cryptic epitopes. The BCTD-reactive T cells can be activated by the naturally generated (dominant) C-terminal epitopes of both exogenous and endogenous Rhsp65 and vice versa. Furthermore, certain individual peptides constituting BCTD and their self homologs can also induce protection against AA. These results support a model for the diversification of T cell response to Bhsp65 during the course of AA involving up-regulation of the display of cryptic BCTD coupled with spontaneous induction of T cell response to the cross-reactive dominant C-terminal epitopes of Rhsp65. The identification of disease-regulating cryptic determinants in Ags implicated in arthritis provides a novel approach for immunotherapy of rheumatoid arthritis.

The T cells specific for the carboxyl-terminal determinants of self (rat) heat-shock protein 65 escape tolerance induction and are involved in regulation of autoimmune arthritis

Immunization of Lewis rats with heat-killed Mycobacterium tuberculosis H37Ra leads to development of polyarthritis (adjuvant-induced arthritis; AA) that shares several features with human rheumatoid arthritis (RA). Immune response to the 65-kDa mycobacterial heat-shock protein (Bhsp65) is believed to be involved in induction of AA as well as in experimental modulation of this disease. However, the understanding of several critical aspects of the pathogenesis of AA in the Lewis rat has severely been hampered by the lack of information both regarding the level as well as epitope specificity of tolerance to the mammalian self (rat) homologue of Bhsp65, 65-kDa rat heat-shock protein (Rhsp65), and about the functional attributes of the T cell repertoire specific for this self protein. In this study, we established that tolerance to Rhsp65 in the Lewis rat is incomplete, and that the residual T cells primed upon challenge with this self hsp65 are disease regulating in nature. We also have defined the T cell epitopes in the C-terminal region within Rhsp65 that contribute predominantly to the immune reactivity as well as the AA-protective effect of this self protein. Furthermore, the T cells primed by peptides comprising these C-terminal determinants can be efficiently restimulated by the naturally generated epitopes from endogenous Rhsp65, suggesting that self hsp65 might also be involved in natural remission from acute AA. These novel first experimental insights into the self hsp65-directed regulatory T cell repertoire in AA would help develop better immunotherapeutic approaches for autoimmune arthritis.

Drug-induced autoimmunity

PURPOSE OF REVIEW

Presentation of different mechanism of drug-induced autoimmunity and highlighting of new developments.

RECENT FINDINGS

Drugs can induce autoimmune diseases by their pharmacological properties. Injection of certain drugs into the thymus can alter positive selection in the thymus and elicit autoimmune reactions. Peripheral tolerance can be broken by increasing the expression of LFA-1 adhesion molecule on T cells. This can be related to the inhibition of intracellular kinases. Alternatively, a drug specific immune response might elicit autoimmunity by cross-reactivity: the drug reactive T cells might be cross-reactive with certain peptide antigens and possibly autoantigens.

SUMMARY

Drug-specific immune responses are well described. They have a great tendency to be cross-reactive with peptide antigens. This 'immunological' cause of autoimmunity elicited by drugs may occur more frequently than thought. It connects the field of drug hypersensitivity with drug-induced autoimmunity.

Major peptide autoepitopes for nucleosome-centered T and B cell interaction in human and murine lupus

The potential cross-reactivity of normal T and B cells to nuclear antigens is vast, probably due to their "education" by apoptotic cell antigens in generative lymphoid organs. Despite this "nucleocentric repertoire," as we call it, the peripheral immune system normally remains tolerant or ignorant of the products of apoptosis. However, the T helper (Th) cells, and also B cells of lupus, have a regulatory defect in the expression of CD40 ligand (CD40L). A sustained hyper-expression of CD40L by lupus T cells can be triggered by sub-threshold stimuli, and is associated with impaired phosphorylation of Cbl-b, a critical downregulatory molecule in T cell signal transduction. This CD40L hyper-expression abnormally prolongs co-stimulatory signals to autoimmune B cells, and it probably instigates APC (dendritic cells, resting anti-DNA B cells, and macrophages) to present apoptotic cell autoantigens in an immunogenic fashion. We have identified the dominant nucleosomal epitopes that are critical for cognate interactions between autoimmune Th cells and anti-DNA B cells in lupus. By scanning of overlapping synthetic peptides, and by mass spectrometry of naturally processed peptides, five major epitopes in nucleosomal histones were localized, namely H1'(22-42), H2B(10-33), H3(85-105), H4(16-39), and H4(71-94). The autoimmune T cells as well as B cells of lupus recognize these epitopes, and with age, autoantibodies against the peptide epitopes cross-react with nuclear autoantigens. Moreover, the peptide autoepitopes can be promiscuously presented and recognized by lupus T cells in the context of diverse MHC alleles. This cross-reactivity opens up the possibility of developing "universally" tolerogenic peptides for therapy of lupus in humans despite their MHC diversity. Indeed, tolerogenic therapy with a single histone peptide epitope can halt the progression of established glomerulonephritis in lupus-prone mice by "tolerance spreading" that inactivates a broad spectrum of autoimmune T and B cells in concert.

Naturally processed chromatin peptides reveal a major autoepitope that primes pathogenic T and B cells of lupus

Major autoepitopes for pathogenic Th cells of lupus were previously found in core histones of nucleosomes by testing overlapping synthetic peptides. To detect other dominant epitopes, we eluted peptides from MHC class II molecules of a murine lupus APC line that was fed with crude chromatin. The eluted peptides were purified by reverse-phase HPLC and tested for their ability to stimulate autoimmune Th clones, and then analyzed by mass spectrometry. Amino acid sequences of stimulatory fractions revealed three new autoepitopes. Two of the epitopes were homologous to brain transcription factor BRN-3, whereas the third sequence was homologous to histone H1'(22-42). H1'(22-42) stimulated autoimmune Th cells to augment the production of pathogenic antinuclear Abs, and was much more potent than other nucleosomal epitopes in accelerating glomerulonephritis in lupus-prone (SWR x NZB)F(1) (SNF(1)) mice. Remarkably, a marked expansion of Th1 cells recognizing the H1'(22-42) epitope occurred spontaneously in SNF(1) mice very early in life. A significant proportion of H1'(22-42)-specific T cell clones cross-reacted with one or more core histone epitopes, but not with epitopes in other lupus autoantigens. The H1'(22-42) epitope was also recognized by autoimmune B cells, and with the onset of lupus nephritis, serum autoantibodies to the H1'(22-42) epitope become increasingly cross-reactive with nuclear autoantigens. Convergence of T and B cell epitopes in H1'(22-42) and its ability to elicit a cross-reactive response make it a highly dominant epitope that could be targeted for therapy and for tracking autoimmune T and B cells.

Regulatory defects in Cbl and mitogen-activated protein kinase (extracellular signal-related kinase) pathways cause persistent hyperexpression of CD40 ligand in human lupus T cells

To identify intrinsic defects in lupus, we studied short-term, CD4(+) T cell lines that were established from 16 lupus patients (active or inactive) and 15 normal subjects by stimulating once with anti-CD3, anti-CD28, and IL-2. After resting, the pure CD4(+) T cells were exposed to anergy-inducing stimulation with plate-bound anti-CD3 mAb in the absence of APC. Lupus T cells showed prolonged high level expression of CD40 ligand (CD40L, CD154) even in the face of anergy protocol, which shut down CD40L expression in normal T cells. The sustained CD40L expression in lupus T cells did not correlate with memory status or Th deviation, and was relatively independent of IL-2 or other autocrine or paracrine signals via CD28 or CTLA-4. Cyclosporin A could block CD40L expression by lupus T cells when added early during the anti-CD3 stimulation period, but only partially when added later, indicating that another mechanism regulates the prolonged hyperexpression of CD40L besides the Ca(2+) --> calcineurin-dependent NF-AT pathway. When exposed to the anergy protocol, lupus T cells, in marked contrast to normal T cells, did not phosphorylate Cbl/Cbl-b but continued to express strongly phosphorylated extracellular signal-regulated kinase (ERK); U0126, a specific inhibitor of mitogen-activated protein kinase kinase --> ERK, could block both the early and the prolonged hyperexpression of CD40L. Thus, pathways regulating the activities of Cbl and one particular mitogen-activated protein kinase, ERK, are involved in the prolonged hyperexpression of CD40L in lupus T cells.