Molecular mimicry between HIV-1 and antigen receptor molecules: a clue to the pathogenesis of AIDS

Cross-reactivity of HIV vaccine responses and the microbiome

PURPOSE OF REVIEW

A successful human immunodeficiency virus-type 1 (HIV-1) vaccine will require immunogens that induce protective immune responses. However, recent studies suggest that the response to HIV-1 and perhaps other viruses may be altered by immune system exposure to intestinal microbiota-antigens. This review will discuss select aspects of these studies.

RECENT FINDINGS

Naïve CD4 T and B cell repertoires can be imprinted by intestinal microbiota-antigens to respond to virus epitopes prior to virus infection. A multiclade envelope (Env) gp145 DNA prime, recombinant adenovirus type 5 boost vaccine tested in a HIV Vaccine Trials Network (HVTN) phase IIb human vaccine efficacy trial (HVTN 505) induced a dominant gp41-reactive antibody response that was non-neutralizing and cross-reactive with intestinal microbiota. This vaccine regimen also induced a dominant gp41-reactive, intestinal microbiota-cross-reactive gp41 antibody response in neonatal and adult Rhesus macaques. Studies of naïve CD4 T cells have demonstrated cross-reactivity to both HIV-1 and influenza peptides.

SUMMARY

HIV-1 Env vaccine-induced CD4 T and B cell responses can originate from a pool of intestinal microbiota-cross-reactive immune cells. Moreover, intestinal microbiota-cross-reactive HIV-1 Env antibodies are ineffective in protection against HIV-1 infection. Thus, intestinal microbiota-imprinting of the B cell repertoire may be one of several roadblocks to the induction of protective HIV-1 antibodies.

Prevalence, morbidity, and therapy of hepatitis E virus infection in pediatric renal allograft recipients

BACKGROUND

Hepatitis E virus (HEV) infection in immunocompromised patients such as solid organ transplant recipients may bear a high risk of becoming a chronic infection with progression to liver cirrhosis. So far, data on HEV infection in pediatric renal transplant recipients are limited.

METHODS

This single-center cohort study investigated period prevalence, morbidity, and treatment of HEV infection in 90 pediatric renal allograft recipients aged 9.9 ± 5.6 years at transplantation (58.9% males). HEV serology was determined by enzyme-linked immunosorbent assay and immunoblot, HEV replication by quantitative nucleic acid testing.

RESULTS

Twelve of 90 (13.3%) patients were HEV seropositive, and 4/90 (4.4%) recipients showed active HEV replication (10³-10⁸ copies/mL, corresponding to 0.5 × 10³ and 0.5 × 10⁸ WHO IU/mL) in serum and stool. In all patients with HEV replication, genotype 3 was identified by partial sequencing of HEV ORF1 and ORF2 and phylogenetic analysis. All patients with HEV replication developed chronic infection associated with moderately elevated liver enzymes. HEV replication was unresponsive to reduction of immunosuppression, whereas ribavirin monotherapy (mean dosage 9.7 ± 3.6 mg/kg per day over 85 ± 11 days) was associated with sustained viral clearance and normalization of liver enzymes in all patients. Ribavirin therapy was associated with reversible, hyporegenerative anemia.

CONCLUSIONS

Given an HEV seroprevalence of 13.3% in pediatric renal transplant recipients and an HEV viremia of 4.4%, HEV infection should be considered in patients with otherwise unexplained elevation of liver enzymes. HEV infection does not necessarily respond to reduction of immunosuppressive therapy, but can be effectively and safely treated with ribavirin.

Human Immunodeficiency Virus Proteins Mimic Human T Cell Receptors Inducing Cross-Reactive Antibodies

Human immunodeficiency virus (HIV) hides from the immune system in part by mimicking host antigens, including human leukocyte antigens. It is demonstrated here that HIV also mimics the V-β-D-J-β of approximately seventy percent of about 600 randomly selected human T cell receptors (TCR). This degree of mimicry is greater than any other human pathogen, commensal or symbiotic organism studied. These data suggest that HIV may be evolving into a commensal organism just as simian immunodeficiency virus has done in some types of monkeys. The gp120 envelope protein, Nef protein and Pol protein are particularly similar to host TCR, camouflaging HIV from the immune system and creating serious barriers to the development of safe HIV vaccines. One consequence of HIV mimicry of host TCR is that antibodies against HIV proteins have a significant probability of recognizing the corresponding TCR as antigenic targets, explaining the widespread observation of lymphocytotoxic autoantibodies in acquired immunodeficiency syndrome (AIDS). Quantitative enzyme-linked immunoadsorption assays (ELISA) demonstrated that every HIV antibody tested recognized at least one of twelve TCR, and as many as seven, with a binding constant in the 10-8 to 10-9 m range. HIV immunity also affects microbiome tolerance in ways that correlate with susceptibility to specific opportunistic infections.

Escape of pathogens from the host immune response by mutations and mimicry. Possible means to improve vaccine performance

The ability of certain pathogens, such as human immunodeficiency, hepatitis C, herpes simplex, influenza viruses, Plasmodium falciparum, etc., to escape from host immune response is generally ascribed to high mutation rate of their genome. We challenge this assumption and propose that molecular mimicry of host antigens by these pathogens could also participate to this resistance. Several studies show that there is no correlation between the mutation rate value of a pathogen and the possibility to develop an effective vaccine. On the other hand, pathogens which do not respond to vaccine are usually reported to display host protein mimicry. We propose to suppress in the thymus the epitopes of the self which are in common with the pathogen. This could be achieved by intrathymic injection of antibodies against this microorganism. These antibodies would be obtained by vaccination of a foreign animal species. It is expected that the negative selection of the CD4(+) and CD8(+) T lymphocytes specific for these epitopes would be prevented, that the number of epitopes recognized as foreign to the host would be increased and that the immune response diversity would be enhanced.

Influence of test technique on sensitization status of patients on the kidney transplant waiting list

The exquisitely sensitive single antigen bead (SAB) technique was shown to detect human leukocyte antigen (HLA) antibodies in sera of healthy male blood donors. Such false reactions can have an impact on critical decisions, especially with respect to the determination of unacceptable HLA-antigen mismatches in patients awaiting a kidney transplant. We tested pretransplant sera of 534 patients on the kidney waiting list using complement-dependent cytotoxicity (CDC), enzyme-linked immunosorbent assay (ELISA) and SAB in parallel. Evidence of HLA antibodies was obtained in 5% of patients using CDC, 14% using ELISA, and 81% using SAB. Among patients without history of an immunizing event, 77% showed evidence of HLA antibodies in SAB. In contrast 98% of these patients were negative in ELISA and CDC. In patients without an immunizing event, SAB-detected antibodies reacted not always weakly but with mean fluorescence intensity (MFI) values as high as 14 440. High-MFI-value antibodies were found in some of these patients with HLA specificities that are rather common in general population, consideration of which would lead to unjustified exclusion of potential kidney donors. False SAB reactions can be unveiled by testing with additional antibody assays. Denial of donor kidneys to recipients based on HLA-antibody specificities detected exclusively in the SAB assay is not advisable.

Extensive viral mimicry of 22 AIDS-related autoantigens by HIV-1 proteins and pathway analysis of 561 viral/human homologues suggest an initial treatable autoimmune component of AIDS

HIV-1 viral proteins, particularly the env protein, are homologous to 22 AIDS autoantigens, suggesting their creation by antiviral antibodies subsequently targeting human homologues. They include antibodies to T-cell receptors, CD4 and CD95, complement components, IgG, TNF and other immune-related proteins. Autoantibodies may compromise the immune system via knockdown of these key proteins, and autoimmune attack on the immune system itself, as supported by immune activation in early stages of infection and during the transition to AIDS. Over 500 human proteins contain pentapeptides or longer consensi, identical to viral peptides. Such homology explains the extensive viral/human interactome, likely related to the ability of viral homologues to compete with human counterparts as binding partners. Pathway analysis of these homologous proteins revealed their involvement in immune-related networks (e.g. natural killer cell toxicity/toll, T-cell/B-cell receptor signalling/antigen processing) and viral and bacterial entry and defence pathways (phagosome/lysosome pathways, DNA sensing/NOD/RIG-1 pathways) relevant to AIDS pathogenesis. At its inception, AIDS may have an autoimmune component selectively targeting the immune system. Immunosuppressive therapy or antibody removal, which has already achieved some success, might be therapeutically beneficial, particularly if targeted at removal of the culpable antibodies, via affinity dialysis.

HIV-1 gp120 AND IMMUNE NETWORK

It has been demonstrated that the immunodominant V3 loop of HIV-1 gp120 and its flanking regions bear sequence and structural homology to the framework and complementarity-determining regions of human immunoglobulins. It has been proposed that the Ig-like domain of gp120 might encode idiotypes and in this way permit HIV-1 entry into the immune regulatory network. This notion is strongly supported by results demonstrating that the anti-V3 loop and anti-Ig antibodies of healthy individuals share complementary structure and that V3 reactive antibodies are present in HIV-negative sera. This might be the mechanism by which HIV induces immunological abnormalities, and it should be taken into consideration in AIDS vaccine development.

HIV immunopathogenesis and strategies for intervention

Therapeutic options aimed at tackling the HIV pandemic face many obstacles. The lack of readily accessible and affordable therapies means that most of those affected go untreated. The array of escape mechanisms used by HIV has undermined the efficiency of many antiviral products and continually represents a barrier to the development of an effective vaccine. Recent developments have seen a shift away from a cytopathic viral model of HIV pathogenesis towards the crucial role of immunopathogenic features--notably generalised immune activation--in the development of AIDS. As conventional vaccine strategies have sought to promote viral neutralisation and suppressive cellular responses, novel strategies that aim to address HIV immunopathogenesis should be sought. We review current opinion on HIV-induced pathogenic immune activation and strategies aimed at eliminating HIV, including a potential role for non-neutralising antibodies as part of a therapeutic vaccine option.

Autoimmunity, anergy, lentiviral immunity and disease

Autoimmune antibodies and autoimmune responses have been characterized in both human HIV infection and the rhesus macaque (RM) non-human primate model of SIV infection and reasoned to contribute to the pathogenesis of AIDS. Many theories for the induction and maintenance of such responses have been entertained including molecular mimicry between HIV proteins and self molecules, CD4+ T cell loss accompanied by loss of normal immune regulation that dictate self-non-self-reactivity, defective negative/positive selection of T cells to name a few. The precise mechanisms that lead to such immune dysfunction is difficult to study in humans. Our lab has been studying such autoimmune responses in both SIV-infected RM and sooty mangabeys (SM), a species from Africa that are naturally infected with SIV but do not display any detectable signs of immune deficiency or autoimmunity. We submit that this model is an important model since it allows for narrowing down those mechanisms and pathways that are a result of lentiviral infection per se from those that specifically cause disease including autoimmunity. During the course of these studies, we have ruled out a role for plasma and cellular viral loads, anti-viral humoral responses and a variety of cell signaling pathways. We have identified select pathways that appear to play roles in the pathogenesis of lentiviral infection and disease. These include pathways involved in innocent bystander killing by apoptosis of CD4+ T cells, role for differential regulation of the cell cycle, and a role for distinct host proteins that get incorporated by the virions as they are assembled and either bud out of CD4+ T cells or exit the cells in the form of multi-vesicular endosomal particles from monocytes/macrophages from SIV-infected disease susceptible RM and disease-resistant SM. We present our current working model and hypotheses that are designed to elucidate differences that are responsible for such distinct outcomes of lentiviral infection, autoimmunity and disease. We believe that such findings have important implications for the design of vaccines against human HIV infection.

Molecular makeup of HIV-1 envelope protein

A broad range of structural, functional, and immunological similarities between HIV-1 gp120 and human proteins, especially those participating in immune responses, highlight gp120 as a pleiotropic protein that can in different ways affect many important functions of the human immune system. Here we described some of these properties of HIV-1 gp120 that represent the main obstacle in the development of effective and safe AIDS vaccine.

Structural, antigenic and evolutionary analyses of immunoglobulins and T cell receptors

We have had the pleasure of collaborating with Allen Edmundson for the past 15 years on the structure, binding properties and evolution of immunoglobulins and T cell receptors. Among the most significant contributions of our joint efforts were: (1) the predictive use of structural features of immunoglobulin domains to model the three-dimensional structures of the immunoglobulin domains of human T-cell receptor alpha and beta chains as well as shark light chains and V(H) domains; (2) the finding that normal humans and other vertebrates express autoantibodies against combining site epitopes of their own T cell receptors; (3) the mapping of the peptide autoepitopes recognized in health, autoimmunity and retroviral infection; and (4) the determination that epitope recognition promiscuity is a characteristic property of the combining sites of IgM immunoglobulins ranging from those of sharks to those of humans. We briefly review the salient findings and status of these studies and indicate the future directions that we will pursue in their continuation.

Natural recognition repertoire and the evolutionary emergence of the combinatorial immune system

The primordial combinatorial immune recognition repertoire arose in the evolution of jawed vertebrates approximately 450 million years ago as a rapid genetic process independent of antigenic selection. We propose that it encompassed the entire repertoire of innate immunity involving molecules that had evolved over billions of years. The 'antigen-driven' compartment involving invasive pathogens operates in 'real time' showing inducibility and increases in affinity. Individuals within a species differ in their repertoires because of distinct antigenic challenges, genetics, or local environmental effects. The 'homeostatic' compartment that recognizes invariant cell and serum components should be conserved in all individuals of a species. The potential to recapitulate the entire recognition spectrum must be regenerated during the formation of new species. Evidence for the capacity of the combinatorial response to encompass the entire preexisting repertoire was obtained in studies of natural human IgG antibodies present in intravenous immunoglobulin. Since essential cellular recognition and regulatory elements are conserved throughout evolution, we propose that the natural antibodies of sharks, the most anciently emerged vertebrates to possess the combinatorial immune response, will resemble those of mammals in showing specificity for the conserved recognition/regulatory molecules. If verified, this hypothesis will establish the fundamental importance of natural antibodies not only in defense, but in regulation and functional homeostasis of the individual.

Proposition of treatment to improve the immune response: possible application to AIDS

The molecular similarity between certain human antigenic determinants with those of HIV has been already described. In this matter, we have previously demonstrated, by a chromatographic method, the cross reactivity of human serum albumin with HIV gp 120. The hypothesis that this similarity could be one of the reasons why the virus escapes to the immune system is presented in this paper and a treatment is proposed to enhance the efficiency of the immune response: it is based on the blocking of the determinants of the self, expressed in the thymus, which are in common with the virus. Repeated injections within the thymus of neutralizing antibodies against the pathogen, obtained from a sufficiently distant animal species and purified by affinity chromatography, would prevent the T cells of the host recognizing these epitopes, common to the host and to the virus, from clonal deletion and would improve the immune response.

Pretransplant serum IgA concentration and IgA-anti-Fab autoantibody activity as prognostic indicators of kidney graft survival

IgA concentration and IgA-anti-Fab autoantibody activity were tested in pretransplant sera of 308 kidney graft recipients. Recipients with a serum IgA concentration of 2 g/l or greater had a 1-year graft survival rate of 83%, compared with a 68% rate in recipients with serum IgA of less than 2 g/l (P < 0.005). Serum IgA concentration and IgA-anti-Fab autoantibody activity were significantly associated (r = 0.38, P < 0.0001). Recipients with a high pretransplant IgA-anti-Fab activity had a significantly better graft survival rate (81%) than patients with low pretransplant IgA-anti-Fab (67%, P < 0.025). When IgA-anti-Fab and serum IgA were considered together, 137 recipients with high IgA-anti-Fab and high serum IgA had a 86% 1-year graft survival rate, which was significantly better than the 63% survival rate in patients with low IgA-anti-Fab and low serum IgA (P < 0.0005). The pretransplant serum IgA level and IgA-anti-Fab autoantibody activity were excellent predictors of kidney graft outcome.

Association of immune complexes and plasma viral load with CD4+ cell depletion, CD8+ DR+ and CD16+ cell counts in HIV+ hemophilia patients. Implications for the immunopathogenesis of HIV-induced CD4+ lymphocyte depletion

OBJECTIVE

There is evidence that HIV induces CD4+ depletion in part by the formation of immune complexes (IC) that attach to CD4+ blood lymphocytes. In the present study we examined the relationship of IC-coated CD4+ blood cells with retroviral replication in HAART-treated patients.

PATIENTS AND METHODS

52 hemophilia patients were studied from 1997 to 1999. Lymphocyte subsets, IgM, IgG and gp120 on CD4+ blood cells, in vitro responses of lymphocytes to mitogens, plasma neopterin and plasma viral load were measured.

RESULTS

Patients with detectable viral replication and without ICs on CD4+ blood lymphocytes had a lower viral load (4100 versus 21000 HIV-1 mRNA copies/ml; P = 0.079) and higher CD4+ cell counts (310/microl versus 161/microl; P = 0.035) than patients with ICs on circulating CD4+ lymphocytes. Among patients with < 80 HIV-1 mRNA copies/ml, IC- individuals had slightly higher CD4+ lymphocyte counts than IC+ patients (384/microl versus 316/microl; n.s.). Further evidence for the clinical relevance of the ICs was obtained when 18 patients who had an undetectable viral load at previous investigations were analyzed. Among patients with a stable undetectable viral load, CD4+ counts increased in 6 of 8 IC- but in none of 2 IC+ individuals. In patients whose viral load increased during the observation period, 5 of 6 IC- but none of 2 IC+ individuals showed higher CD4+ cell counts. Impaired virus killing is suggested by lower CD16+ (35/microl versus 107/microl; P = 0.016), higher CD3+ DR+ (178/microl versus 66/microl; P = 0.006), and higher CD8+ DR+ (142/microl versus 34/microl; P = 0.017) cell counts in IC(-) patients compared to IC- patients without detectable viral load. Strong retroviral replication induced strong T cell dysfunctions. Fewer CD3+ 25+ blood lymphocytes (19/microl versus 47/microl; P = 0.006) and a lower in vitro response of T lymphocytes to the mitogens Con A (RR: 0.3 versus 1.2; P=0.023) and CD3 mab (RR: 0.5 versus 2.4; P = 0.012) was observed in IC+ patients with detectable versus undetectable viral load.

CONCLUSION

Our data suggest that ICs on circulating CD4+ blood lymphocytes are primarily associated with CD4+ lymphocyte depletion whereas the plasma viral load is primarily associated with decreased T lymphocyte activation, lower CD16+ counts, and higher CD8+ DR+ lymphocytes which might be the effector cells for virus elimination.

AIDS epidemic at the beginning of the third millennium: time for a new AIDS vaccine strategy

Current expansion of AIDS pandemic significantly accelerates AIDS vaccine research resulting in development and clinical testing of several AIDS vaccine candidates. At the same time, available experimental and clinical data demonstrate that current AIDS vaccine strategy is unsuccessful resulting in development of inefficient and harmful vaccines. This overview briefly summarizes reported results which point out the requirement for moratorium on the current clinical trials of HIV-1 gp120/160 vaccines and urgent need for development of a new, efficient and safe AIDS vaccine strategy.

Graft-protective role of high pretransplantation IgA-anti-Fab autoantibodies: confirmatory evidence obtained in more than 4000 kidney transplants. The Collaborative Transplant Study

BACKGROUND

Preliminary studies showed an excellent success rate of kidney grafts in patients with high pretransplantation serum levels of IgA autoantibodies directed against the Fab region of the human IgG molecule.

METHODS

With the collaboration of 30 centers from around the world, we attempted to verify the role of IgA-anti-Fab autoantibodies in kidney transplantation in an entirely new series of 4316 cadaveric kidney transplants, with special consideration of presensitized and poorly HLA-matched recipients.

RESULTS

In agreement with previously published preliminary findings, 147 recipients with a high pretransplantation IgA-anti-Fab of >1000 had a 2-year kidney graft survival rate of 88+/-3% (+/- SE), compared with an 80+/-1% rate in 851 recipients with a low IgA-anti-Fab of <60 (P = 0.02). Even in patients at an increased risk of graft rejection, high pretransplantation IgA-anti-Fab autoantibody activity was associated with superior graft survival. Among 815 presensitized patients, 31 had a high pretransplantation IgA-anti-Fab activity of >1000 and their 2-year graft survival rate was 94+/-4%, in contrast to a 71+/-4% rate in 165 presensitized recipients with a low IgA-anti-Fab of <60 (P = 0.02). Of 2294 recipients who received a kidney with > or =3 HLA-A+B+DR mismatches, 79 recipients had a high pretransplantation IgA-anti-Fab of >1000 and a 2-year graft survival rate of 90+/-4%, as compared with a 79+/-2% rate in 459 patients with a low IgA-anti-Fab of <60 (P = 0.04).

CONCLUSIONS

The present study confirms that kidney graft recipients with high pretransplantation IgA-anti-Fab activity have excellent graft survival, and it extends this observation to presensitized recipients and poor HLA matches.

Evolutionary stable strategy: a test for theories of retroviral pathology which are based upon the concept of molecular mimicry

The genetic makeup of animal and plant populations is determined by established principles and concepts. Ecology and evolution provide a basic theoretical framework for understanding how genetic changes occur in populations. Whether these rules can be applied to host retroviral populations is unknown. Individuals infected with the human immunodeficiency virus (HIV) contain within their bodies a viral population. This population is known as a viral quasispecies. Located in the transmembrane protein of HIV-1 is the viral sequence Gly-Thr-Asp-Arg-Val. Previous immunological studies have shown that viral antibody is produced in response to this five-amino-acid sequence. Antibody to this viral sequence also crossreacts and binds to a related peptide sequence found on certain immune cells. This related sequence, Gly-Thr-Glu-Arg-Val, is found on immune cells bearing a structure known as the major histocompatibility complex (MHC). The viral transmembrane sequence, Gly-Thr-Asp-Arg-Val, can be substituted with alanine residues utilizing site-directed mutagenesis. This creates a viral clone devoid of the genetic similarity with the MHC. Chimpanzees progressing to AIDS contain both sequences of interest. Suppression of the chimpanzee quasispecies utilizing anti-retroviral drugs is proposed. This action serves to suppress the presence of the viruses containing the sequence Gly-Thr-Asp-Arg-Val. When viral load has been reduced significantly, a drug resistant, alanine altered clone is to be introduced in large numbers. The concept of evolutionary stable strategy predicts that a viable HIV clone with alanine residues can genetically dominate the viral population. Immune system recognition of the alanine sequence is likely to result in renewed antibody production. Antibodies to the alanine containing viral sequence should not recognize or bind to the MHC. Immunological parameters can then be measured to determine the physiological impact of eliminating a sequence responsible for molecular mimicry between virus and host.

Anti-V3 and anti-IgG antibodies of healthy individuals share complementarity structures

It was recently shown that antibodies reactive with a peptide from the tip of the HIV-1NY5 gp120 V3 loop (V3 peptide) are present not only in sera of HIV-positive patients but also in sera of healthy HIV-negative individuals. In the present study, we show that V3 peptide reactive antibodies are predominantly IgM in sera of HIV negative individuals and that a fraction of the IgG anti-V3 antibodies exhibit features of autoantibodies. These antibodies were purified by chromatography on IgG-sepharose columns from sera as well as from purified IgG anti-V3 antibodies. A higher IgG anti-V3 reactivity was detected in autoantibody preparations from HIV-positive sera as compared with the reactivity of sera and purified antibodies from HIV-negative individuals. This was confirmed by solid phase binding of IgG anti-V3 antibodies both to V3 and to human IgG F(ab')2 antigens. The autoantibodies did not bind to peptides that share sequence similarity with V3 peptide indicating a high epitope specificity. The detection of antibodies against HIV epitopes in HIV-negative individuals may suggest that anti-V3 antibodies after HIV infection represent at least in part a secondary immune response.

Human immunodeficiency virus V3 peptide-reactive antibodies are present in normal HIV-negative sera

A structural relation between consensus sequences of the portion of HIV-1 gp120 involving the V3 loop (V3 peptide) and the variable domains of human immunoglobulin members of the VH-III gene family was proposed to trigger an imbalance of the idiotypic network during the course of HIV infection. Thus, the repertoires of immunoglobulins in healthy individuals should contain antigenic determinant(s) complementary to particular V3 loop epitope(s). In this study we investigated the specific binding to the V3 peptide of antibodies present in sera of HIV-positive and of clinically normal HIV-negative subjects. Two groups of HIV-positive sera differing in antibody titers to V3 peptide, arbitrarily referred here as high- and low-reactive HIV-positive sera, were distinguished on the basis of an ELISA. Antibodies were affinity purified on V3 peptide and their titers in both HIV-negative and low-reactive HIV-positive sera were nearly superimposable and much lower than the titers of those from high-reactive HIV-positive sera. Also, the quality of the two groups of antibodies differed: much higher amounts of soluble V3 peptide were needed to partly compete the binding of antibodies from HIV-negative sera to insoluble V3 peptide as compared with those from HIV-positive sera, suggesting that the latter had higher affinity for V3 peptide. All of the affinity-purified antibodies bound poorly to unrelated peptides, even to those sharing sequence similarity with the V3 peptide. The present observations suggest that in HIV infection antigen-driven affinity maturation of preimmune immunoglobulins with idiotypes complementary to V3 epitope(s) participating in physiological autoreactivity might be at work.

Recognition of defined epitopes by affinity-purified anti-immunoglobulin fab autoantibodies isolated from HIV-infected humans

Infection of humans with HIV-1 has previously been independently shown to result in the generation of autoantibodies (AAbs) reactive with immunoglobulin Fab fragments (Heidelberg), and with autoantibodies to T-cell receptors (TCRs) (Tucson). Here, we carry out epitope mapping studies of affinity-purified AAbs to Fab fragments prepared from individual HIV-positive patients for their capacity to bind recombinant constructs and peptide-defined epitopes modeling TCR and Ig light chains. Some affinity-purified autoantibodies reacted strongly with TCRs expressed by intact T-cells, and recombinant Valpha/Vbeta constructs as well as with certain synthetic peptide epitopes. The binding reactions of affinity-purified AAbs of individual patients were distinct, and the AAb preparations consisted of populations of polyclonal lgs as reflected in specificity and isotype. AAb pools from individual patients all bound particular regions of TCR and Ig chains defined by comprehensive peptide synthesis including the CDR1 and Fr3 segments of the variable domains and the joining segment/switch peptide. In addition, other reactivities to restricted regions of alpha, beta and lambda light chains were documented. These results substantiate the cross-reactivity of TCR and Ig-Fab determinants, and are consistent with the hypothesis that autoantibodies arising as a consequence of HIV infection can have an immunomodulatory role.

CD4 depletion in HIV-infected haemophilia patients is associated with rapid clearance of immune complex-coated CD4+ lymphocytes

The predominant immunological finding in HIV+ haemophilia patients is a decrease of CD4+ lymphocytes during progression of the disease. Depletion of CD4+ lymphocytes is paralleled by an increase in the proportion of immune complex-coated CD4+ cells. We examined the hypothesis that the formation of immune complexes on CD4+ lymphocytes is followed by rapid clearance of immune complex-coated CD4+ lymphocytes from the circulation. In this study, the relationship of relative to absolute numbers of immune complex-loaded CD4+ blood lymphocytes and their association with viral load were studied. Two measurements of relative and absolute numbers of gp120-, IgG- and/or IgM-loaded CD4+ lymphocytes were analysed in HIV+ and HIV- haemophilia patients, with a median interval of approx. 3 years. Immune complexes on CD4+ lymphocytes were determined using double-fluorescence flow cytometry and whole blood samples. Viral load was assessed using NASBA and Nuclisens kits. Whereas the proportion of immune complex-coated CD4+ lymphocytes increased with progression of the disease, absolute numbers of immune complex-coated CD4+ lymphocytes in the blood were consistently low. Relative increases of immune complex-coated CD4+ blood lymphocytes were significantly associated with decreases of absolute numbers of circulating CD4+ lymphocytes. The gp120 load on CD4+ blood lymphocytes increased in parallel with the viral load in the blood. These results indicate that immune complex-coated CD4+ lymphocytes are rapidly cleared from the circulation, suggesting that CD4+ reactive autoantibodies and immune complexes are relevant factors in the pathogenesis of AIDS. Relative increases of immune complex-positive cells seem to be a consequence of both an increasing retroviral activity as well as a stronger loading with immune complexes of the reduced number of CD4+ cells remaining during the process of CD4 depletion. The two mechanisms seem to enhance each other and contribute to the progressive CD4 decrease during the course of the disease.

IgA class antibodies and flow cytometric cross-matching in renal transplantation

BACKGROUND

The established method of pretransplant cross-matching does not detect IgA antibodies, and IgA antibodies have thus been ignored when assessing patients for transplantation. The aim of this study was to detect IgA allo- and autoreactive antibodies using flow cytometry and to correlate the results with transplant outcome.

METHODS

Pretransplant sera from 231 sequential renal recipients were tested for serum IgA levels and antibodies directed against the Fab portion of the human IgG molecule. Fifty-nine recipients with sufficient stored donor lymphocytes were also tested by flow cytometry for donor-specific alloantibodies of the IgA isotype.

RESULTS

Graft survival was improved in recipients with higher IgA levels. High IgA anti-Fab levels led to a significantly higher 1-year graft survival (P<0.05). Graft survival was further enhanced where both serum IgA and IgA anti-Fab were raised (P<0.01). Although the mean IgA level tended to be higher for recipients with a positive IgA flow cytometric cross-match (FCXM), the IgA FCXM was not associated with increased IgA anti-Fab, suggesting that the IgA FCXM is detecting a different subset of IgA reactivity. Additionally, for primary grafts, a positive IgA FCXM was not associated with enhanced graft survival.

CONCLUSIONS

Within the repertoire of IgA activity, there are two recognizable groups, the IgA anti-Fab specificity, which is significantly associated with enhanced graft survival, and that detected by the IgA FCXM, which surprisingly is more likely to be positive in less sensitized first grafts and is not associated with enhanced graft survival.

Association of viral load in plasma samples of HIV-infected hemophilia patients with autoantibodies and gp120-containing immune complexes on CD4+ lymphocytes

OBJECTIVE

We investigated whether the induction of antilymphocyte autoantibodies and immune complexes is associated with the activity of HIV replication.

METHODS

Viral HIV-1 RNA was measured in the plasma samples of 84 HIV+ hemophilia patients and correlated with the IgM, IgG, IgM/IgG and IgM/IgG/gp120 load of circulating CD4+ lymphocytes, CD4+ and CD8+ cell counts, plasma neopterin levels and in vitro T-cell responses to mitogens and pooled allogeneic stimulator cells.

RESULTS

Compared to patients with no immune complexes, on circulating CD4+ lymphocytes, viral load was increased in patients with IgM, IgM/IgG or IgM/IgG/gp120 complexes. Sequential analysis of HIV+ patients showed that peaks of retroviral activity were associated with the subsequent formation of CD4+ lymphocyte-reactive IgM and IgG autoantibodies and gp120-containing immune complexes.

CONCLUSION

The induction of autoantibodies and immune complexes attached to CD4+ lymphocytes is associated with periods of increased viral activity in HIV-infected patients.

Relationship between progression of disease and immunoglobulin A-anti-Fab-/F(ab')2 autoantibodies in patients with head and neck cancer

Patients with malignant tumors of the head and neck often have immune defects. Higher serum immunoglobulin (Ig)A levels were reported in this group of patients. We investigated whether IgA-anti-Fab- or IgA-anti-F(ab')2 autoantibodies, which have been shown to correlate with severe dysfunction of the immune system, also appear in patients with head and neck cancer. Sera of 110 patients with squamous cell carcinoma (SCCHN), eight patients with adenoid cystic carcinoma, and 57 healthy control subjects were tested by enzyme-linked immunosorbent assay for IgA-anti-Fab autoantibody activity. Patients with head and neck cancer showed a higher IgA-anti-Fab activity (optical density (OD) = 399; n = 118) than did healthy control subjects (OD = 84; n = 57; p < 0.0001). An association between stage of disease and IgA-anti-Fab activity could be established in patients with SCCHN. Patients with stage IV disease had a significantly higher IgA-anti-Fab activity (OD = 538; n = 51) than had patients with stage I disease (OD = 283; n = 18; p < 0.05). Patients with stage II (OD = 293; n = 13) or stage III (OD = 379; n = 28) disease had intermediate activity. Also a higher IgA-anti-Fab activity than in healthy control subjects could be shown in the eight patients with adenoid cystic carcinoma (OD = 314; n = 8; p < 0.01). The highest IgA-anti-Fab activity was observed in eight patients with SCCHN who died within 6 months after testing (OD = 1004; n = 8), suggesting an association between autoimmunity and final desintegration of physiologic body functions. The occurrence of IgA-anti-Fab/IgA-anti-F(ab')2 autoantibodies might be interpreted as an aspect of immune deficiency in patients with malignant tumors of the head and neck.

The presence of antibodies against HIV peptides in the sera of alloimmune mice and thalassemic patients is due to a polyclonal activation mechanism

This paper analyses the HIV-1 gp120 epitope specificity and activation mechanisms (i.e., polyclonal versus oligoclonal) of antibodies present in the sera of alloimmune mice and humans. Sera from CBA mice engrafted with C57BL/6 lymphoid cells significantly reacted against the gp120-derived peptide as 261-270, which shares high homology with the membrane-proximal domain of HLA class II beta-chains (HLA/ gp120) and against the HIV gp120 V3 loop-derived peptides DP32 (HIV-1 MN-derived as 302-334) and C53 (HIV-1 IIIB-derived as 304-318). The same sera also reacted against the HIV-unrelated peptide necdin. Moreover, sera from BALB/c mice injected with LPS presented antibodies reacting against both HIV-related and -unrelated peptides, suggesting that similar mechanisms are shared in alloimmune and LPS-treated mice. A similar analysis was then performed on the sera of patients affected with beta-thalassemia major, receiving at least 10 blood transfusions/year. In particular, 15 of 58 (26%) sera from HIV-uninfected thalassemic patients showed a significantly reactivity against the HLA/gp 120-derived peptides. Moreover, 22 of 58 (38%) sera from the same cohort showed a significant reactivity against DP32 peptide. This reactivity was related to a polyclonal activation mechanism since the DP32-reactive sera significantly bound a panel of HIV-unrelated peptides, as observed by testing 22 sera against necdin, 21 against HSP65 kDa, 21 against amyloid-1, and 17 against MAGE-1 peptides. Moreover, a significant increase of IgG concentration was also observed in all thalassemic sera, when compared to healthy controls, without regard to the anti-gp120 antibody reactivity. Taken together, these results indicate that (i) allogeneic stimuli may induce anti-gp120 antibodies in CBA and in 38% of polytransfused patients and (ii) this reactivity is related to a polyclonal activation mechanism but not to a heightened concentration of IgG.

Does AIDS emerge from a disequilibrium between two complementary groups of molecules that mimic MHC?

There is increasing evidence that a disturbance of self-nonself-recognition plays an important role in the immunopathogenesis of AIDS. Here, Caner Susal, Volker Daniel and Gerhard Opelz speculate that the immune system is balanced between two groups of molecules that mimic major histocompatibility complex (MHC) proteins; AIDS is suggested to emerge as a consequence of human immunodeficiency virus (HIV) disturbing this balance in favor of anti-MHC class II responses.

Sequential occurrence of IgM, IgM/IgG, and gp120-IgM/IgG complement complexes on CD4+ lymphocytes in relation to CD4+ blood lymphocyte depletion in HIV+ hemophilia patients: results of a 10-year study

The concept of autoimmune mechanisms playing an integral role in the pathogenesis of HIV disease is rapidly gaining ground. In this study, we determined IgM and IgG antibodies, complement fragments and gp120 on the surface of CD4+ lymphocytes using double-fluorescence flow cytometry. Sequential analysis demonstrated an inverse relationship of autoantibodies and CD4+ lymphocyte counts in the peripheral blood. HIV+ patients without autoantibodies (16/104 = 15%) had the highest CD4+ blood cell counts (324 +/- 264/microliters; mean +/- SD). CD4+ counts were successively lower in patients with complement-fixing IgM (243 +/- 240/microliter), complement-fixing IgG and IgM (139 +/- 138/microliter), or gp120-IgM/IgG complement complexes on the surface of CD4+ cells (38 +/- 45/microliter, P = 0.03). Individual patient profiles show that IgM autoantibodies typically are formed early after HIV infection and appear to deplete CD4+ lymphocytes very slowly, whereas complement-fixing IgG autoantibodies are generated at a later stage and deplete CD4+ lymphocytes more efficiently. The presence of both soluble gp120 and complement-fixing autoantibodies on CD4+ lymphocytes is associated with very low CD4+ cell counts and coincides with progression to terminal disease. Early during HIV infection autoantibody production is rather unstable, but it becomes more stable with disease progression and persists in advanced stages of the disease. These data suggest that autoantibody formation against CD4+ lymphocytes is a pathogenic mechanism for CD4+ cell depletion.

In vitro cytokine treatment of B cell defects in HIV-infected hemophilia patients

HIV-infected patients exhibit defects in B cell differentiation and in the IL-6 response of B cells, in association with autoantibody formation against T cells. These autoantibodies have been implicated as important factors in the development of immunodeficiency disease. As the restoration of defective B cell responses might prevent autoantibody formation and the resulting immunosuppression, we studied whether in vitro treatment with recombinant IL-2 (rIL-2), recombinant IL-4 (rIL-4) or recombinant IL-6 (rIL-6) might restore the response of B cells of HIV-infected patients. B cells of 6 HIV-negative hemophilia patients, 4 HIV-positive patients at CDC stage II, III, 4 HIV-positive patients at CDC stage IV, and 6 healthy controls were tested in Staphylococcus aureus Cowan I (SAC-I)-stimulated B cell cultures and Pokeweed mitogen (PWM)-stimulated allogeneic B and T cell cocultures. B cell differentiation was assessed in a reverse hemolytic plaque assay and by ELISA determination of IgM, IgG and IL-6 in culture supernatants. In vitro application of rIL-6 resulted in suppression of both elevated unstimulated and mitogen-stimulated B cell responses in a dose-dependent manner which was in part due to feedback inhibition. PWM- and SAC-I-stimulated IgG and IgM responses, respectively, could be restored after addition of 10 U/ml rIL-2 in HIV-negative patients, but not in HIV-positive patients. Addition of rIL-4 to cultures resulted in suppression of both unstimulated and mitogen-stimulated IL-6 secretion and B cell responses. Severely depressed B cell responses in CDC IV patients were not significantly affected by cytokine application. These results indicate that defective Ig responses in HIV-negative patients may be restored by rIL-2 treatment whereas HIV-induced B cell defects are not corrected by supply of T cell help or cytokines promoting B cell growth and differentiation.

Human complement proteins C3b, C4b, factor H and properdin react with specific sites in gp120 and gp41, the envelope proteins of HIV-1

Recently we reported the basic phenomenon of an interaction between the envelope glycoproteins of HIV-1 gp120 and gp41 and components of the human complement system, i.e. activated C4 (C4b) and activated C3 (C3b) and the complement regulator proteins factor H and properdin. In this study we analyze these interactions in detail. Using 46 overlapping peptides of gp120 attached to microtiter plates, binding of activated human C3 to 6 regions in gp120 was found (aa 100-129, 161-190, 231-250, 301-328, 410-449, 470-499). In competition assays with soluble peptides, representatives of four of these regions were capable to partially inhibit C3b binding to immobilized gp120. Activated human C4 interacted only with peptides covering aa 410-449, but both in direct binding assays and fluid phase inhibition studies. The multi-reactivity of gp120 with C3b was also supported by the fact that gp120 agglutinated erythrocytes coated with C3b. Guided by partial aa sequence homology of gp120 and human C4b binding protein (C4bp) as well as human properdin we detected binding of anti-properdin to aa 100-129 in gp120 and of anti-C4bp to aa 410-449 in gp120. This cross-reactivity was also confirmed by a monoclonal antibody directed against aa 416-443 of gp120, which could be shown to bind C4bp. Interestingly, aa 310-328, part of the V3-loop, were found to show an aa sequence similarity to human complement receptor type 3 (alpha-chain). Consequently, of the 4 (or possibly 6) interaction sites of gp120 with activated human C3, 3 may bind due to imitation of either properdin, CR3 or C4bp. In addition to C4b and C3b, we detected interaction of factor H with gp120; it selectively bound to aa 102-129. Using 14 overlapping peptides of gp41 attached to plates, we identified 4 areas in gp-41 (aa 561-585, 587-605, 615-635, 651-675) which bound human factor H. All of them except the first region partially inhibited factor H binding to gp41 in competition assays with soluble peptides. Properdin bound only to 2 regions (aa 584-614, 651-675). The first 3 sites in gp41 were already shown by us to share homology to sites in human C3. The region around aa 651-675 now also turned out to be similar to human C3. These data demonstrate that the interaction of both, gp120 and gp41, with the complement system is polyvalent and complex.(ABSTRACT TRUNCATED AT 400 WORDS)

The T cell receptor and AIDS pathogenesis

An idiotypic network model of AIDS pathogenesis is described in which the T cell receptor plays a role both in infection and as a target of autoimmunity. This is an extension of a previously published autoimmunity model, and provides explanations for several otherwise puzzling aspects of AIDS pathogenesis. In the model HIV-specific T cells are preferentially infected, and HIV, acting as an antigen, stimulates the expansion of the infectable pool of T cells. The HIV variants that are most strongly selected are those that are recognized by the most helper T cells. HIV and suppressor T cells are subject to the same selective environment, and consequently undergo a process of convergent selection to resemble each other more and more with time. Eventually immunity against HIV cross-reacts with suppressor T cell idiotypes, disrupting the normal regulation of helper T cells. Autoimmunity ensues. The model leads to novel vaccine and therapy approaches involving the targeting and elimination of HIV-specific T cells.

Semen alloantigens and lymphocytotoxic antibodies in AIDS and ICL

More than 90% of people with AIDS develop circulating immune complexes (CICs) and lymphocytotoxic antibodies (LCTAs). Animals infected with HIV, however, never display CICs or LCTAs, and remain healthy. Similarly, HIV-infected people who do not develop CICs or LCTAs also do not progress to AIDS. The appearance of CICs and LCTAs is, however, highly prognostic for AIDS and death. Since HIV infection does not, per se, lead to the development of CICs and LCTAs, other causes are likely. One such cause, for which both epidemiologic and experimental evidence exists, is semen. Semen components include sperm, seminal fluid, lymphocytes, and sometimes infectious agents, including HIV, mycoplasmas, and herpes and hepatitis viruses, all of which independently cause immune suppression. Extensive evidence demonstrates sperm (and various viruses) contains many proteins mimicking the CD4 protein of T-helper cells, while HIV, mycoplasmas, and seminal fluid mimic class II MHC proteins of other lymphocytes. We identify a large number of protein sequences that display such mimicry using computer homology searching, and demonstrate experimentally that sperm antibodies specifically precipitate antibodies against class II MHC mimics such as mycoplasmas, which in turn precipitate antibodies to lymphocyte antigens. These data prove that immunologic exposure to sperm and lymphocytes (as may occur in receptive anal intercourse, needle sharing, or blood transfusions) is theoretically capable of initiating lymphocytotoxic autoimmunity. Such autoimmunity may play a significant role in the pathogenesis of AIDS, and will need to be addressed clinically in high risk individuals regardless of HIV status and regardless of the success of anti-HIV prophylaxis and treatment.

Soluble HLA class I and class II concentrations in factor VIII and PCC preparations

Soluble HLA class I (sHLA-CI) and class II (sHLA-CII) molecules were quantitated in 11 commercially available factor VIII and prothrombin complex concentrate (PCC) preparations by enzyme-linked immunosorbent assays (ELISA). In 4 preparations, we detected traces of sHLA-CI (0.01-0.07 mg/l), and in 7 hemostatic preparations small amounts of sHLA-CII molecules (0.02-0.28 mg/l). The concentrations of these contaminant molecules are unequivocally below the mean values of sHLA in human plasma (sHLA-CI: 1.01 +/- 0.72 mg/l; sHLA-CII: 1.53 +/- 2.44 mg/l). Based on the total amount of chronically administered factor VIII or PCC, contaminating sHLA molecules may be in principle able to exert immunomodulatory effects in patients treated with such preparations.

Five myths about AIDS that have misdirected research and treatment

A number of widely repeated and factually incorrect myths have pervaded the AIDS research literature, misdirecting research and treatment. Five of the most outstanding are: 1) that all risk groups develop AIDS at the same rate following HIV infection; 2) that there are no true seroreversions following HIV infection; 3) that antibody is protective against HIV infection; 4) that the only way to treat AIDS effectively is through retroviral therapies; and 5) that since HIV is so highly correlated with AIDS incidence, it must be the sole necessary and sufficient cause of AIDS. A huge body of research, reviewed in this paper, demonstrates the falsity of these myths. 1) The average number of years between HIV infection and AIDS is greater than 20 years for mild hemophiliacs, 14 years for young severe hemophiliacs, 10 years for old severe hemophiliacs, 10 years for homosexual men, 6 years for transfusion patients of all ages, 2 years for transplant patients, and 6 months for perinatally infected infants. These differences can only be explained in terms of risk-group associated cofactors. 2) Seroreversions are common. Between 10 and 20 percent of HIV-seronegative people in high risk groups have T-cell immunity to HIV, and may have had one or more verified positive HIV antibody tests in the past. 3) Antibody, far from being protective against HIV, appears to be highly diagnostic of loss of immune regulation of HIV, and some evidence of antibody-enhancement of infection exists. 4) Non-retroviral treatments of HIV infection, including safer sex practices, elimination of drug use, high nutrient diets, and limited reexposure to HIV and its cofactors have proven to be effective means of preventing or delaying onset of AIDS. 5) Many immunosuppressive factors, including drug use, multiple concurrent infections, and exposure to alloantigens, are as highly correlated with AIDS risk groups as HIV. These data are more consistent with AIDS being a multifactorial or synergistic disease than a monofactorial one.

Immunosuppression by a noncytolytic virus via T cell mediated immunopathology. Implication for AIDS

HIV is basically a non- or poorly cytocidal virus. Therefore, HIV infections in humans represent an apparent perversity in the balance between the host immune system and infectious agent: This noncytopathic virus infects macrophages, antigen presenting cells, helper T cells and other host cells which are then destroyed by the CD8+ T cell immune response. Thus, HIV infects some of the key cells involved in immune reactions and therefore induces the immune system to destroy itself and thereby enables the virus to persist. Accordingly, immunosuppression is not a cause of HIV cytopathogenicity but a consequence of conventional T cell mediated immunopathology that destroys macrophages antigen presenting cells, T helper cells and facilitates infection by trivial intracellular parasites which eventually cause fatal disease. This immunopathological view of AIDS is testable and, if correct, impinges on rationales for AIDS prevention and treatment.

Panel of anti-gp120 monoclonal antibodies reacts with same nuclear proteins in uninfected cells as those recognized by autoantibodies from patients with systemic lupus erythematosus

Mouse monoclonal antibodies (MAbs) directed against the HIV-1 gp120 envelope protein were screened for their reactivity with intracellular antigens expressed in normal uninfected monocytes by indirect immunofluorescence and immunoblotting. Some of these MAbs reacted with the nuclei of normal uninfected cells, producing three main staining patterns by indirect immunofluorescence. Western blot analysis showed that these monoclonal antibodies recognize peptides of various molecular weights present in nuclei preparations of normal monocytes. Reactivity with peptides of similar molecular weight was also detected in sera from both HIV-infected individuals and patients with systemic lupus erythematosus. This evidence for antigenic similarities between HIV-1 gp120 and nuclear antigens represents a novel example of molecular mimicry of self-antigens by HIV envelope proteins, which supports the involvement of mechanisms of autoimmunity in HIV disease pathogenesis through recruitment of autoimmune responses to self-structures by HIV antigens.

Autoreactivity in HIV-infected individuals does not increase during vaccination with envelope rgp160

The HIV-1 envelope protein contains several regions with amino acid homology to HLA class I and class II molecules. We evaluated possible changes in antibody responses to those regions during vaccination with rgp 160 produced in a baculovirus system. Forty asymptomatic HIV-infected patients with CD4 cell counts above 400 were vaccinated with rgp 160. Twenty-one patients were tissue-typed as HLA A2. Sixty-two percent of these patients exhibited cytotoxic lymphocyte antibodies directed to CD8+, HLA A2 cells. This cytotoxicity decreased during HIV gp160 vaccination. In order to further characterize the specificity of these responses, analogues of HLA class I and HLA-DR peptides were chemically synthesized together with their correct HIV-1 gp160 sequences. Enzyme-linked immunosorbent assays (ELISA) with sera from before, during and after immunization were performed with HIV proteins, peptides and their homologues. All patients showed an increase in their previously poor specific T-cell activation to gp160. Fourteen patients developed increased avidities or titres to HIV proteins and/or peptides. Contrarily, serum IgG titers to the HLA homologous peptides were initially low and decreased further during the course of vaccination. This decrease occurred in the majority of patients, 35-40 of the 40 individuals, depending on the antigen. Independent measures of autoantibodies to Ro/SS-A and La/SS-B remained undetectable.

Comparative study of antibodies that are associated with disease progression in HIV disease

Two types of antibodies which previously were found to be inversely associated with CD4+ cell counts and which may contribute to the progression of HIV disease were measured in parallel in 55 serum samples of 7 longitudinally tested HIV-infected patients (4 homosexual men, 3 haemophilic men) and in 15 serum samples from 15 patients with advanced AIDS. HIV-infection enhancing antibodies were determined in the presence of near-physiologic human complement concentration using a complement receptor type 2 (CR2) carrying HIV-target cell line. IgG and IgA class autoantibodies directed against human IgG-Fab fragments were measured in specific ELISA assays. In agreement with our previous studies obtained in HIV-seropositive haemophilic patients, significant negative correlations were found between CD4+ cell counts and IgG anti-Fab and IgA anti-Fab antibodies (Spearman correlation coefficient r = -0.587, P < 0.0001; and r = -0.269, P = 0.024, respectively). A significant positive correlation was observed between complement-dependent enhancing antibodies and IgA anti-Fab antibodies (r = 0.408, P = 0.003), whereas the correlation with IgG anti-Fab antibodies was only weak (r = 0.288, P = 0.034). Serum samples with high titres of complement-dependent enhancing antibodies had almost 3 times higher IgA anti-Fab autoantibody activity than sera with low titres (P = 0.0038). Our findings indicate that the two disease markers in HIV disease, enhancing antibodies and autoantibodies directed against the Fab moiety of IgG, are not identical. However, anti-Fab antibodies may contribute to complement-dependent HIV infection enhancement.

Association of IgA-anti-Fab autoantibodies with disease stage in head-and-neck cancer

Patients with head-and-neck cancer commonly have immune defects. It was reported that these patients have raised serum IgA levels. We investigated whether IgA-anti-Fab autoantibodies, which occur in association with immune dysfunction, are present in patients with head-and-neck cancer. Sera of 101 patients with squamous-cell carcinoma (SCCHN) and 8 patients with adenoid cystic carcinoma (ACCHN) of the head and neck were tested in ELISA for IgA-anti-Fab autoantibody activity. IgA-anti-Fab serum activity was significantly higher in both SCCHN and ACCHN patients than in healthy controls. In patients with SCCHN, an association between disease stage and IgA-anti-Fab activity was established. Stage-IV patients had significantly higher IgA-anti-Fab than stage-I patients or healthy controls. Stage-II and stage-III patients had intermediate levels. Extremely high IgA-anti-Fab activity was observed in 7 patients who died within 6 months following testing, suggesting a relationship of autoimmunity with terminal disintegration of physiological body functions. IgA-anti-Fab autoantibodies may explain the occurrence of immune defects in patients with head-and-neck cancer.

HLA antigens and resistance to HIV

The role of histocompatibility antigens in HIV infection has been investigated by several approaches. Thus the haplotype A1B8DR3 that is usually linked to autoimmune disorders seems to be associated with accelerated progression to AIDS. Cross-reactivity between MHC antigens and HIV-1 proteins is evident from alloimmunization experiments in mice and xenoimmunization of monkeys with human cells. Furthermore, recent reports suggest that some individuals with uncommon HLA antigens may be resistant to HIV infection. In addition to expressing cross-reacting antigens with HLA, HIV also exhibits substantial amounts of host beta-2 microglobulin and HLA-DR attached to its surface. Taken together, these data are stimulating new hypotheses relevant for AIDS pathogenesis. Based on alloimmunization, novel approaches have also been proposed in attempts to promote an effective immune response to HIV.