Molecular mimicry between human endogenous retrovirus clone 4-1 and HLA class I antigen with reference to the pathogenesis of systemic lupus erythematosus

Human endogenous retroviruses and the inflammatory response: A vicious circle associated with health and illness

Human Endogenous Retroviruses (HERVs) are derived from ancient exogenous retroviral infections that have infected our ancestors' germline cells, underwent endogenization process, and were passed throughout the generations by retrotransposition and hereditary transmission. HERVs comprise 8% of the human genome and are critical for several physiological activities. Yet, HERVs reactivation is involved in pathological process as cancer and autoimmune diseases. In this review, we summarize the multiple aspects of HERVs' role within the human genome, as well as virological and molecular aspects, and their fusogenic property. We also discuss possibilities of how the HERVs are possibly transactivated and participate in modulating the inflammatory response in health conditions. An update on their role in several autoimmune, inflammatory, and aging-related diseases is also presented.

How Retroviruses and Retrotransposons in Our Genome May Contribute to Autoimmunity in Rheumatological Conditions

More than 200 human disorders include various manifestations of autoimmunity. The molecular events that lead to these diseases are still incompletely understood and their causes remain largely unknown. Numerous potential triggers of autoimmunity have been proposed over the years, but very few of them have been conclusively confirmed or firmly refuted. Viruses have topped the lists of suspects for decades, and it seems that many viruses, including those of the Herpesviridae family, indeed can influence disease initiation and/or promote exacerbations by a number of mechanisms that include prolonged anti-viral immunity, immune subverting factors, and mechanisms, and perhaps “molecular mimicry”. However, no specific virus has yet been established as being truly causative. Here, we discuss a different, but perhaps mechanistically related possibility, namely that retrotransposons or retroviruses that infected us in the past and left a lasting copy of themselves in our genome still can provoke an escalating immune response that leads to autoimmune disease. Many of these loci still encode for retroviral proteins that have retained some, or all, of their original functions. Importantly, these endogenous proviruses cannot be eliminated by the immune system the way it can eliminate exogenous viruses. Hence, if not properly controlled, they may drive a frustrated and escalating chronic, or episodic, immune response to the point of a frank autoimmune disorder. Here, we discuss the evidence and the proposed mechanisms, and assess the therapeutic options that emerge from the current understanding of this field.

Retroviruses in the pathogenesis of systemic lupus erythematosus: Are they potential therapeutic targets?

The pathogenesis of systemic lupus erythematosus (SLE) is characterised by the hyper-activation of immunologic pathways related to the antiviral response. Exogenous and endogenous retroviruses, by integrating their DNA templates in the host cell genome, may epigenetically control the transcription of genes involved in the immune response. Furthermore, their nucleic acids or neo-synthesized proteins could stimulate the sensor molecules placed upstream the inflammatory cascade. Exogenous retroviruses, like human immunodeficiency virus, have been associated to SLE-like manifestations or to a fair SLE diagnosis. In addition, there is some evidence confirming a pathogenic role of human endogenous retroviruses in SLE. In line with these data, the use of antiretroviral agents could represent an attractive opportunity in the future therapeutic algorithms of this disease, but studies are still missing.

Molecular mimicry in systemic lupus erythematosus

Systemic lupus erythematosus is a multi-systemic autoimmune disease distinguished by the presence of various autoantibodies. Like most autoimmune diseases, systemic lupus erythematosus is believed to be induced by a combination of genetic, immunologic, and environmental factors, mainly infectious agents. Molecular mimicry between an infectious antigen and self-components is implicated as a pivotal mechanism by which autoimmune diseases such as systemic lupus erythematosus are triggered. Here we review the current evidence of molecular mimicry between different infectious agents and systemic lupus erythematosus.

Immune abnormalities induced by human endogenous retroviral peptides: with reference to the pathogenesis of systemic lupus erythematosus

P15E is a specific sequence among the envelope gene (env)-encoded transmembrane proteins of exogenous and endogenous retroviruses. A synthetic peptide (CKS- 17) that shows homology to this p15E region in several species of retrovirus is known to induce immune abnormalities. In this study, we examined the effect of a synthetic peptide derived from a region of human endogenous retrovirus (HERV) clone 4-1 (lambda4 - 1) similar to sequences of CKS-17 on the induction of systemic lupus erythematosus (SLE)-related immune abnormalities. Our results indicated that this peptide could induce T-cell activation and anergy in normal peripheral blood mononuclear cells, and the peptide could also promote the production of interleukins IL-6 and IL-16. These phenomena are representative immune abnormalities observed in SLE patients. Thus, our findings support the possibility that HERV acts as a pathogen in human SLE.

Relationship between CD4(+)/CD8(+) T cell ratio and T cell activation in multiple myeloma: reference to IL-16

We found that the ratio of CD4(+) to CD8(+) T cells (CD4/CD8 ratio) was decreased in patients with multiple myeloma (MM) and that this decrease was significantly related to an increase of human leukocyte antigen (HLA)-DR expression by CD8(+) (but not CD4(+)) T cells (P<0.005). In addition, the serum level of interleukin (IL)-16 was significantly higher in stage III MM patients than in healthy controls (P<0.001). The decrease of CD4(+) T cells in MM may be mediated by activation of CD8(+) T cells derived cytokine IL-16. In addition, these T cell phenotypic changes and the IL-16 level appear to be useful indicators of disease activity.

Endogenous retroviruses in systemic lupus erythematosus: candidate lupus viruses

Although the etiology of systemic lupus erythematosus (SLE) remains unclear, there is substantial circumstantial evidence that the development of SLE is dependent on environmental, genetic, and retroviral factors. SLE patients produce high titer antibodies to various retroviral proteins, including Gag, Env, and Nef of HIV and HTLV, in the absence of overt retroviral infection. We review the factors linking HERVs to SLE and consider the various processes utilized by endogenous retroviruses in the etiopathogenesis of SLE. In particular, we consider the role of HTLV-1-related endogenous sequence (HRES-1) in SLE. We propose that molecular mimicry between HRES-1 and the small ribonucleoprotein complex initiates the production of autoantibodies, leading to immune complex formation, complement fixation, and pathological tissue deposition.

Lessons from similarities between SLE and HIV infection

OBJECTIVE

We attempted to obtain deeper understanding of systemic lupus erythematosus (SLE) and human immunodeficiency virus (HIV) infection through comparative studies between both diseases.

METHOD

For this purpose, we reviewed and discussed lessons from similarities in both diseases based on our own and reported findings in literatures.

RESULT

Such comparative studies may contribute to the progress in understanding the clinical or pathogenetic features of these diseases.

CONCLUSION

Further studies into the relationship between SLE and HIV infection may bring to light important clues to assist in the development of better treatments for each disease.

A possible pathogenic role of CD8+ T cells and their derived cytokine, IL-16, in SLE

Current investigations into the role of CD8+ T cells and their derived cytokine, interleukin (IL)-16, in the induction of CD4+ T cell abnormalities in systemic lupus erythematosus (SLE) were reviewed and discussed on the basis of results mainly obtained in our laboratory.