Endogenous retroviruses in systemic lupus erythematosus: candidate lupus viruses

Early human migration determines the risk of being attacked by wolves: ethnic gene diversity on the development of systemic lupus erythematosus

The prevalence of systemic lupus erythematosus (SLE) varies significantly based on ethnicity rather than geographic distribution; thus, the prevalence is higher in Asian, Hispanic, and Black African populations than in European populations. The risk of developing lupus nephritis (LN) is the highest among Asian populations. Therefore, we hypothesize that human genetic diversity between races has occurred through the early human migration and human genetic adaptation to various environments, with a particular focus on pathogens. Additionally, we compile the currently available evidence on the ethnic gene diversity of SLE and how it relates to disease severity. The human leukocyte antigen (HLA) locus is well established as associated with susceptibility to SLE; specific allele distributions have been observed across diverse populations. Notably, specific amino acid residues within these HLA loci demonstrate significant associations with SLE risk. The non-HLA genetic loci associated with SLE risk also varies across diverse ancestries, implicating distinct immunological pathways, such as the type-I interferon and janus kinase-signal transducers and activators of transcription (JAK-STAT) pathways in Asians, the type-II interferon signaling pathway in Europeans, and B cell activation pathway in Africans. Furthermore, assessing individual genetic susceptibility using genetic risk scores (GRS) for SLE helps to reveal the diverse prevalence, age of onset, and clinical phenotypes across different ethnicities. A higher GRS increases the risk of LN and the severity of SLE. Therefore, understanding ethnic gene diversity is crucial for elucidating disease mechanisms and SLE severity, which could enable the development of novel drugs specific to each race.

Viral Infections and Systemic Lupus Erythematosus: New Players in an Old Story

A causal link between viral infections and autoimmunity has been studied for a long time and the role of some viruses in the induction or exacerbation of systemic lupus erythematosus (SLE) in genetically predisposed patients has been proved. The strength of the association between different viral agents and SLE is variable. Epstein-Barr virus (EBV), parvovirus B19 (B19V), and human endogenous retroviruses (HERVs) are involved in SLE pathogenesis, whereas other viruses such as Cytomegalovirus (CMV) probably play a less prominent role. However, the mechanisms of viral-host interactions and the impact of viruses on disease course have yet to be elucidated. In addition to classical mechanisms of viral-triggered autoimmunity, such as molecular mimicry and epitope spreading, there has been a growing appreciation of the role of direct activation of innate response by viral nucleic acids and epigenetic modulation of interferon-related immune response. The latter is especially important for HERVs, which may represent the molecular link between environmental triggers and critical immune genes. Virus-specific proteins modulating interaction with the host immune system have been characterized especially for Epstein-Barr virus and explain immune evasion, persistent infection and self-reactive B-cell "immortalization". Knowledge has also been expanding on key viral proteins of B19-V and CMV and their possible association with specific phenotypes such as antiphospholipid syndrome. This progress may pave the way to new therapeutic perspectives, including the use of known or new antiviral drugs, postviral immune response modulation and innate immunity inhibition. We herein describe the state-of-the-art knowledge on the role of viral infections in SLE, with a focus on their mechanisms of action and potential therapeutic targets.

Predictors and outcome of systemic lupus erythematosus (SLE) admission rates in a large teaching hospital in sub-Saharan Africa

Although it was previously believed that systemic lupus erythematosus was uncommon among Africans, it has become increasingly apparent that the incidence is higher, and socioeconomic challenges such as physician shortages, poor medical facility access, and poor health literacy may worsen prognosis. This retrospective study examines characteristics and outcomes of hospitalized systemic lupus erythematosus patients over a two-year period and serves as a baseline for comparison for future studies to examine the outcomes with the provision of more dedicated care. There were 51 patient admissions over a two-year period, with a mean duration from start of illness to admission of approximately two years. Duration of admission ranged from one to 140 days with a mean period of 26.12 days (SD ± 26.6). There were 22 deaths (43.1% of admissions), which were mainly due to infections and renal complications. Factors associated with risk of death in regression analysis were: infections, fever, disease flare, musculoskeletal involvement, amenorrhea, depression, a clinical finding of hepatomegaly, and chest infection. Understanding the effect and outcome of systemic lupus erythematosus across different countries can elucidate the role of genetic, environmental, and other causative factors in the progression of the disease.

Targeting human immunodeficiency virus type 1 with antibodies derived from patients with connective tissue disease

During the budding process, human immunodeficiency virus (HIV) acquires several cellular proteins from the host. Thus, antibodies against self antigens found in sera patients with autoimmune disorders may cross react with host-derived or the HIV-specific proteins gp120 and gp41 on the viral envelope and probably neutralize HIV infection. To verify this hypothesis, 88 sera from HIV negative patients suffering from systemic lupus erythematosus (SLE) and other autoimmune disorders were analysed for cross reacting antibodies against HIV-1 by Western blot and FACS analysis indicating that antibodies cross-react with epitopes expressed on HIV infected or non-infected cells. Virus capture assays revealed that HIV-1IIIBwas directly recognized by 60% of sera from patients with autoimmune disorders. Sera were also tested in HIV neutralization assays with stimulated T cells. Reduction of the viral load by patient sera correlated with their reactivity in Western blot analysis. Complement further enhanced the reduction of viral titres, although no complement-mediated lysis was observed. These data suggest a possible protective role of auto-antibodies against HIV infection in lupus patients.

Lupus nephritis class I accompanied by tubulointerstitial nephritis with marked T-lymphocyte infiltration in an HTLV-1 positive patient

We herein describe the case of a 40-year-old Japanese male who was admitted to our hospital because of a continuous remittent fever lasting 1 month. He fulfilled the items of the classification criteria for the diagnosis of systemic lupus erythematosus (SLE). The administration of 20 mg per day of oral prednisolone completely diminished his clinical symptoms. However, his renal biopsy performed 1 day after the admission showed marked pathognomonic characteristics. Not only did his glomeruli show class I lupus nephritis with mesangial depositions of IgG, IgA, C3, and C1q, but also tubulointerstitial nephritis with marked T-lymphocyte infiltration. These infiltrated T cells partly had nuclear atypia. The patient was positive for human T cell leukemia virus type 1 (HTLV-1) antibodies. Furthermore, clonal rearrangements of T cell receptor-gamma chain gene was detected in the DNA extracted from his kidney sections by the polymerase chain reaction (PCR) method. A second renal biopsy 6 months after the prednisolone treatment showed that the infiltrating T lymphocytes had markedly diminished. This is the first case report of lupus nephritis class I with tubulointerstitial nephritis, which might include oncogenic T lymphocytes, in an HTLV-1 positive patient.

HERVs in neuropathogenesis

In humans, exogenous retroviruses are known to cause immunodeficiency and neurological disease. While endogenous retroviruses are firmly established pathogens in other species, the human endogenous retroviruses (HERVs) may well be considered as emerging pathogens. HERVs also exhibit complex interactions with exogenous retroviruses and herpesviruses. Two neurological disorders in particular are associated with HERVs: multiple sclerosis (MS) and schizophrenia. HERV-H/F and HERV-W are specifically activated both in the circulation and the central nervous system (CNS) in a majority of MS patients, and particularly, the envelopes (env transcription and Env proteins) appear strongly associated with disease activity. Interferon beta (IFN-beta) therapy is well-established for MS. IFN-beta is also known to have anti-retroviral activities toward exogenous retroviruses (HIV and HTLV-I). New reports show that IFN-beta also mediate down-regulation of HERV-H/F and HERV-W in MS patients. HERV-W and HERV-K transcription (gag and pol) appears, to some extent, to be up-regulated in the circulation and the CNS of patients with schizophrenia. The expression of anti-HERV-W Gag reactive epitopes is reported to be down-regulated in the brain but up-regulated in the blood from schizophrenia patients. The pathogenic potential of HERVs certainly merits further studies.

Long interspersed nuclear elements (LINE-1): potential triggers of systemic autoimmune disease

Recent advances have identified immune complexes containing nucleic acids as stimuli for toll-like receptors and inducers of type I interferon (IFN). While a similar mechanism may serve to amplify immune system activation and production of inflammatory mediators in vivo in the context of systemic autoimmune diseases, the initial triggers of autoimmunity have not been defined. In this review, we describe a category of potential inducers of autoimmunity, the endogenous retroelements, with a particular focus on long interspersed nuclear elements (LINE-1, L1). Increased expression of L1 transcripts or decreased degradation of L1 DNA or RNA could provide potent stimuli for an innate immune response, priming of the immune system, and induction of autoimmunity and inflammation. Genomic and genetic variations among individuals, sex-related differences in L1 regulation, and environmental triggers are among the potential mechanisms that might account for increased L1 expression. Induction of type I IFN by L1-enriched nucleic acids through TLR-independent pathways could represent a first step in the complex series of events leading to systemic autoimmune disease.

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.

Role of endogenous retroviruses in autoimmune diseases

Molecular epidemiologic proof that HERVs and other retroelements are involved in autoimmunity or other disorders is complicated by their large numbers in the human genome. As discussed, most HERVs are no longer functional or active because of the accumulation of mutations, frameshifts, and deletions. Detection or quantification of HERV transcripts that may be pathologically involved in a particular autoimmune disease thus is often compromised by the presence in great excess of related, but nonfunctional, RNA. This phenomenon should not deter active work in the field, although it will require development of improved methods to discriminate accurately between closely related RNA transcripts. Development of improved immunologic methods to precisely identify epitopes on autoantigens or rare self-reactive T-cell clones may further implicate HERVs and the other repetitive elements in regulation of the immune system in health and disease.

The occurrence of systemic lupus erythematosus in an asymptomatic carrier of human T-cell lymphotropic virus type I

A 63-year-old asymptomatic carrier of human T-cell lymphotropic virus type I (HTLV-1) infection was admitted because of chest oppression, a high-grade fever, polyarthralgia, and erythematous rashes. Laboratory examination revealed lymphocytopenia, proteinuria, and high titers of antinuclear antibodies and antidouble-stranded DNA antibody; thus, she was diagnosed as having systemic lupus erythematosus (SLE). This case indicates that HTLV-1 infection might be related with the pathogenesis of SLE.

Infections and SLE

Viral and bacterial infections may serve as an environmental trigger for the development or exacerbation of systemic lupus erythematosus (SLE) in the genetically predetermined individual. In addition, SLE patients are more prone to develop common (pneumonia, urinary tract infection, cellulitis, sepsis), chronic (tuberculosis), and opportunistic infections possibly due to inherit genetic and immunologic defects (complement deficiencies, mannose-binding lectin [MBL] polymorphisms, elevated Fcgamma III and GM-CSF levels, osteopontion polymorphism), but also due to the broad spectrum immunosuppressive agents that are part of therapy for severe manifestations of the disease. Hence, SLE patients are considered a high-risk population, where identification and treatment of chronic infections such as tuberculosis, hepatitis B or human immunodeficiency virus, are important prior to the institution of immunosuppression so as to prevent reactivation or exacerbation of the infection. Infections in SLE patients remain a source of morbidity and mortality. A caveat often encountered is to distinguish between a lupus flare and an acute infection; in such cases parameters including elevated CRP (and adhesion molecules) may aid in the diagnosis of infection. Recent research has provided convincing evidence that EBV infection may play a major role not only in molecular mimicry but also in aberrations of B cells and apoptosis leading to a state of perpetual heightened immune response in SLE.

Recurrent Pulmonary Thromboembolism in a Patient with Systemic Lupus Erythematosus and HIV-1 Infection Associated with the Presence of Antibodies to Prothrombin: A Case Report

BACKGROUND

The coexistence of human immunodeficiency virus (HIV) infection and systemic lupus erythematosus (SLE) is being increasingly reported and, because of the immunological disturbances demonstrated in HIV-infected patients, diagnostic and therapeutic difficulties may arise when the 2 conditions coexist. Antiphospholipid antibodies are demonstrable in patients with both conditions, but clinical manifestations of the antiphospholipid syndrome (APS) in HIV-infected patients, although reported, are uncommon.

METHODS

We describe a patient with HIV infection and SLE who manifested 4 episodes of deep vein thrombosis (DVT) complicated by pulmonary embolism. Enzyme-linked immunosorbant assay was used to test for the presence of antiphospholipid antibodies, including anticardiolipin antibodies, anti- beta 2-glycoprotein 1 antibodies, and antiprothrombin antibodies (anti-PT). Additionally, we performed a computer-assisted search of the literature (via the Medline database) to identify all reported cases of HIV infection plus SLE.

RESULTS

We document the case of 35-year-old African woman with HIV infection and SLE who developed recurrent episodes of DVT and pulmonary embolism in the presence of anti-PT and discuss in depth the pathogenic role of these antibodies and the clinical challenges posed to clinicians by the coexistence of HIV and SLE in the same patient.

CONCLUSIONS

Immunological reconstitution in HIV-infected patients contributes to the appearance of multiple autoimmune conditions, including SLE and APS. The recognition of the coexistence of these autoimmune disorders in HIV-infected patients has important implications in the treatment of and prognosis for these individuals.

Development of lupus nephritis in a patient with human T-cell lymphotropic virus type I-associated myelopathy

A 77-year-old Japanese man with a 14-year history of human T-cell lymphotropic virus type I-associated myelopathy developed pancytopenia, proteinuria, renal dysfunction, and hypocomplementemia. Antinuclear antibody and anti-double-stranded DNA antibody test results were positive, and circulating immune complexes were detected. A renal biopsy showed diffuse and global mesangiocapillary proliferation with extensive subendothelial deposits. Immunofluorescence microscopy showed strong granular staining for immunoglobulins and complements in the mesangium and along capillary walls. Electron microscopy showed numerous mesangial and subendothelial electron-dense deposits. From these findings, systemic lupus erythematosus and diffuse global lupus nephritis were diagnosed. This is a rare case of a patient developing lupus nephritis during the long-term course of human T-cell lymphotropic virus type I-associated myelopathy.

Bacterial lipopolysaccharide both renders resistant mice susceptible to mercury-induced autoimmunity and exacerbates such autoimmunity in susceptible mice

The initiation and severity of systemic autoimmune diseases are influenced by a variety of genetic and environmental factors, in particular bacterial infections and products. Here, we have employed bacterial lipopolysaccharide (LPS), which non-specifically activates the immune system, to explore the involvement of innate immunity in mercury-induced autoimmunity in mice. Following treatment of mouse strains resistant [DBA/2 (H-2(d))] or susceptible [SJL(H-2(s))] to such autoimmunity with mercuric chloride and/or LPS or with physiological saline alone (control), their immune/autoimmune responses were monitored. Resistant DBA/2 mice were rendered susceptible to mercury-induced autoimmunity by co-administration of LPS, exhibiting pronounced increases in the synthesis of IgG1 and IgE, high titres of IgG1 deposits in the kidneys and elevated circulating levels of IgG1 antibodies of different specificities. Furthermore, the percentages of the T cells isolated from the spleens of DBA/2 mice exposed to both mercury and LPS that produced pro-inflammatory cytokines were markedly increased by in vitro stimulation with phorbol myristate acetate (PMA) and ionomycin, which was not the case for splenic T cells isolated from mice receiving mercuric chloride, LPS or saline alone. In addition, exposure of susceptible SJL mice to mercury in combination with LPS aggravated the characteristic features of mercury-induced autoimmunity, including increased synthesis of IgG1 and IgE, the production of IgG1 anti-nucleolar antibodies (ANolA) and the formation of renal deposits of IgG1. In summary, our findings indicate that activation of the innate immune system plays a key role in both the induction and severity of chemically induced autoimmunity.

The natural antibody repertoire of sharks and humans recognizes the potential universe of antigens

In ancestral sharks, a rapid emergence in the evolution of the immune system occurred, giving jawed-vertebrates the necessary components for the combinatorial immune response (CIR). To compare the natural antibody (NAb) repertoires of the most divergent vertebrates with the capacity to produce antibodies, we isolated NAbs to the same set of antigens by affinity chromatography from two species of Carcharhine sharks and from human polyclonal IgG and IgM antibody preparations. The activities of the affinity-purified anti-T-cell receptor (anti-TCR) NAbs were compared with those of monoclonal anti-TCR NAbs that were generated from a systemic lupus erythematosus patient. We report that sharks and humans, representing the evolutionary extremes of vertebrate species sharing the CIR, have NAbs to human TCRs, Igs, the human senescent cell antigen, and to numerous retroviral antigens, indicating that essential features of the combinatorial repertoire and the capacity to recognize the potential universe of antigens is shared among all jawed-vertebrates.

Lack of immunological or molecular evidence for a role of mouse mammary tumor retrovirus in primary biliary cirrhosis

BACKGROUND & AIMS

Recent observations, including a pilot clinical trial, have suggested that a human mouse mammary tumor virus (MMTV) causes primary biliary cirrhosis (PBC). We attempted to confirm such data.

METHODS

We obtained sera from 101 patients (53 with PBC and 48 controls), fixed liver sections from 10 patients (8 PBC and 2 controls), fresh liver specimens (6 PBC and 6 controls), and fresh peripheral blood lymphocytes (PBLs) (10 PBC and 10 controls). We studied sera for reactivities against 3 different strains of MMTV virions, MMTV(C3H), MMTV(FM), and MMTV(LA), including goat polyclonal antibodies against MMTV virions, gp52, and p27 as positive controls. We stained liver specimens using polyclonal antibodies against MMTV and gp52 and further examined tissue samples and PBLs for specific MMTV genome sequences.

RESULTS

By Western blot analysis, no detectable reactivity in any of the PBC sera against any of the 3 MMTV strains or MMTV gp52 or p27 was observed. However, viral proteins were recognized by our control positive polyclonal antibodies. We note that 13%-60% of PBC sera presented low reactivity against 2 proteins of approximately 57 and 74 kilodaltons. Such reactivity is related to the trace amounts of mitochondrial antigens in the virus preparations derived from murine mammary tumor tissue. No detectable immunohistochemical or molecular evidence for MMTV was found in the liver specimens or PBLs.

CONCLUSIONS

We were unable to recapitulate the data on this specific retroviral etiology of PBC and suggest that such data could be the result of contamination.

High prevalence of an IgG response against murine leukemia virus (MLV) in patients with psoriasis

Increasing evidence suggests that human endogenous retroviruses (HERV) could participate in the pathogenesis of autoimmune diseases such as multiple sclerosis and lupus erythematosus. To assess a possible association of murine leukemia virus (MLV)-like group of HERVs with psoriasis we searched for antibodies against MLV proteins in the sera of patients. We showed that anti-MLV antibodies (total) were detected in both psoriatic and control sera. However, they were detected with a higher frequency in psoriasis when compared with controls (91 vs. 53%, respectively, P=0.001). In addition, the IgG response was dramatically increased in psoriasis (86 vs. 8%, respectively, P<0.0001). This immunoreactivity was observed against the products of both the gag and env genes, and the most antigenic proteins were the gp65-70. Moreover, we observed that anti-p30 MLV antibodies reacted with an epidermal protein with a molecular weight of 50 kDa in protein extracts from both normal and psoriatic skin cultures. These observations suggest that HERVs of the MLV-like group could contribute to the immunopathogenesis of psoriasis.

SLE and infections

Infections are common in systemic lupus erythematosus (SLE), and remain a source of mortality. The types of infections (such as pneumonia, urinary tract infection, cellulitis, and sepsis) in SLE patients are similar to the general population and include the same pathogens (Gram-positive and Gram-negative). SLE patients may also develop opportunistic infections, especially when treated with immunosuppressive agents. As a high-risk population, identification and treatment of chronic infections such as tuberculosis, hepatitis B, or human immunodeficiency virus (HIV), are important prior to the institution of immunosuppression to prevent reactivation or exacerbation of the infection. A common caveat is to distinguish between a lupus flare and an acute infection; judicious use of corticosteroids and cytotoxic drugs is critical in limiting infectious complications. The risk factors associated with susceptibility to disease include severe flares, active renal disease, treatment with moderate or high doses of corticosteroids and/or immunosuppressive agents, and others. Genetic factors (complement deficiencies, mannose-binding lectin, Fcgamma III, granulocyte macrophage colony-stimulating factor [GM-CSF], osteopontin) may predispose certain SLE patients to develop infections. Parameters including C-reactive protein (CRP) and adhesion molecules may help to differentiate an infectious disease from an exacerbation of the disease. Finally, the mechanism of molecular mimicry by specific microbial agents may play a role in the induction of SLE.

Neutralizing interferon alpha as a therapeutic approach to autoimmune diseases

Therapeutic antibodies directed against tumor necrosis factor alpha (TNF-alpha) for the treatment of rheumatoid arthritis, and against the human EGF receptor-2 (HER2) receptor for the treatment of breast cancer have provided significant clinical benefit for the patients. The success of these antibodies has also provided strong support for the possibility that increased activity of cytokines or growth factors is causally implicated in a variety of human diseases. Interferon alpha (IFN-alpha) is induced by viruses (linked by epidemiological studies to autoimmune diseases), has significant direct effects on both epithelial cells and the immune system, and then can be further induced by the autoantibodies and apoptotic cells generated by the actions of IFN-alpha. The direct and deleterious impact on target tissues, the ability to induce an autoimmune response, and the potential for a self-sustaining cycle of induction and damage suggests that IFN-alpha could be a pivotal factor in the development of autoimmune diseases. This review will evaluate the rationale for, possible approaches to, and safety concerns associated with, targeting interferon alpha (IFN-alpha) as a therapeutic strategy for the treatment of autoimmune diseases. While the approach may be applicable to several autoimmune diseases, there will be an emphasis on systemic lupus erythematosus and insulin dependent diabetes mellitus.

Autoimmunity to nucleosomes related to viral infection: a focus on hapten-carrier complex formation

Systemic lupus erythematosus (SLE) is an autoimmune disorder with unknown aetiology. The major hallmark of this disease is the presence of antibodies against nuclear components, including double-stranded (ds)DNA and histones. The disease affects different organs, particularly the skin, kidneys and the nervous system. Although the exact molecular mechanisms underlying the pathophysiological processes in SLE remain unknown, several inherent and environmental factors seem to be involved in the ethiopathogenesis of this disorder. Viruses may be one of the factors that induce the production of autoreactive antibodies although the involved mechanisms are still incompletely understood. One proposed mechanism for virus-induced production of autoantibodies is molecular mimicry. Another mechanism derives from studies with the human polyomavirus BK. In these studies, in vivo binding of the polyomaviruses large T-antigen to chromatin of infected cells may render chromatin immunogenic. The large T-antigen-chromatin complex may thus function as a hapten-carrier model with subsequent production of anti-chromatin antibodies, including anti-dsDNA and anti-histones antibodies. This review focuses on the recent findings suggesting that this model may be applicable for other human viruses associated with SLE.

Role of endogenous retroviruses in autoimmune diseases

Endogenous retroviruses (ERVs) correspond to the integrated proviral form of infectious retroviruses that are trapped within the genome by mutations. Endogenous retroviruses represent a key molecular link between the host genome and infectious viral particles. Proteins encoded by ERVs are recognized by antiviral immune responses and become targets of autoreactivity. Activation of ERVs, such as human ERV-K or a human T-cell lymphotropic virus-related endogenous sequence, may also mediate pathogenicity of Epstein-Barr virus. Endogenous retrovirus peptides can directly regulate immune responses. Thus, molecular mimicry and immunomodulation by ERVs may account for self-reactivity and abnormal T- and B-cell functions in autoimmune disorders.

Prospects for immunotherapeutic proteolytic antibodies

Monoclonal antibodies are suitable for therapeutic applications by virtue of their excellent target binding characteristics (specificity, affinity) and long half-life in vivo. Catalytic antibodies (CAbs) potentially represent a new generation of therapeutics with enhanced antigen inactivation capability. Here, we describe prospects for development of therapeutic CAbs to the envelope protein gp120 of HIV. The strategy consists of exploiting the natural tendency of the immune system to synthesize germline-encoded, serine protease-like CAbs. Lupus patients were found to develop antibodies to a conserved component of the CD4 binding site of gp120, potentially offering a means to obtain human antibodies expressing broad reactivity with various HIV strains. Covalently reactive antigen analogs (CRAs) capable of selective recognition of nucleophilic Abs were synthesized and applied to isolate Fv and L chain catalysts from lupus phage repertoires. CRA binding by the recombinant Ab fragments was statistically correlated with catalytic cleavage of model peptide substrates. A peptidyl CRA composed of residues 421-431 with a phosphonate diester moiety at its C terminus was validated as a reagent that combines noncovalent and covalent binding interactions in recognition of a gp120ase L chain. A general challenge in the field is the apparent instability of the catalytic conformation of the Abs. In reference to therapy of HIV infection, assurance is required that the Abs recognize the native conformation of gp120 expressed as a trimer on the virus surface.