Autoimmune response in AIDS

Autoimmunity and dysmetabolism of human acquired immunodeficiency syndrome

Acquired immunodeficiency syndrome (AIDS) remains ill-defined by lists of symptoms, infections, tumors, and disorders in metabolism and immunity. Low CD4 cell count, severe loss of body weight, pneumocystis pneumonia, and Kaposi's sarcoma are the major disease indicators. Lines of evidence indicate that patients living with AIDS have both immunodeficiency and autoimmunity. Immunodeficiency is attributed to deficits in the skin- and mucosa-defined innate immunity, CD4 T cells and regulatory T cells, presumably relating human immunodeficiency virus (HIV) infection. The autoimmunity in AIDS is evident by: (1) overproduction of autoantibodies, (2) impaired response of CD4 cells and CD8 cells, (3) failure of clinical trials of HIV vaccines, and (4) therapeutic benefits of immunosuppression following solid organ transplantation and bone marrow transplantation in patients at risk of AIDS. Autoantibodies are generated in response to antigens such as debris and molecules de novo released from dead cells, infectious agents, and catabolic events. Disturbances in metabolic homeostasis occur at the interface of immunodeficiency and autoimmunity in the development of AIDS. Optimal treatments favor therapeutics targeting on the regulation of metabolism to restore immune homeostasis.

HIV, 'an evolving species'. Roles of cellular activation and co-infections

Each small variation of the genome of a species can be preserved if it is useful for the survival of the species in a given environment. Within this framework, the finality of the biological cycle of HIV consists in a search for harmony (biological coherence) with man, which is to say a stable condition. Cellular activation appears to be the strategy developed by HIV in order to achieve this coherence. The price of this strategy is the AIDS. The first contact between HIV and immune system appears to determine the subsequent clinical outcome and the future of HIV. Lymphocytic activation varies during the course of the vital cycle of HIV. For each individual, this lymphocytic activation depends on both the HLA repertoire acquired during thymic ontogenesis and the antigenic experience before and after HIV infection. Thus intercurrent infections alter the immune condition of the organism and influence the outcome of HIV. We described a synthetic analysis of the effects of HIV on the surface protein expression and the cellular activation pathways which should provide insights in the evolutionary relationship between HIV and man and should permit to do a more physiological therapeutic approach.

Induction of anti-simian immunodeficiency virus cellular and humoral immune responses in rhesus macaques by peptide immunogens: correlation of CTL activity and reduction of cell-associated but not plasma virus load following challenge

Lipopeptides which carry the N-terminal moiety tripalmitoyl-S-glyceryl-cysteinyl-seryl-seryl (P(3)CSS) have been shown to have effective adjuvant and transmembrane carrier properties. To test the ability of these constructs to immunize against simian immunodeficiency virus [(SIV)(mac)] infection, rhesus macaques, prescreened for expression of the Mamu-A*01 MHC class I molecule, were immunized at regular intervals with lipopeptides corresponding to known SIV(mac) CTL epitopes alone or in combination with multiple antigenic peptides corresponding to neutralizing epitopes. Both humoral and CTL responses were elicited and the monkeys, along with non-immunized control animals, were challenged intravenously with 20 MID(50) of the homologous, uncloned SIV(mac251-32H) grown in rhesus monkey PBMC. Although none of the monkeys were protected from infection, most demonstrated an anamnestic CTL response with epitope-specific CTL precursor frequencies reaching as high as 1 in 20 total PBMC as measured by limiting dilution CTL assay or 25% of all CD8(+) T-cells using tetrameric MHC-I/peptide complexes. A significant inverse correlation between the levels of CTLp and the number of infected cells in circulation was observed. However, no such correlation with the plasma viral load (RNA copies/ml) was evident.

Itchy folliculitis and human immunodeficiency virus infection: clinicopathological and immunological features, pathogenesis and treatment

The predominant itchy folliculitis associated with human immunodeficiency virus (HIV) infection appears to be an eosinophilic folliculitis (EF). This is characterized by lytic degeneration of sebaceous glands and an inflammatory infiltrate in which eosinophils and CD8+ T lymphocytes predominate. All patients have low CD4 counts and present late on in their HIV disease. Lesional distribution is mainly truncal, with a significant proportion also having facial involvement. Our prospective survey has shown that it is impossible to differentiate clinically between infective folliculitis and EF, and we recommend therefore that all cases are biopsied. We review the clinicopathological and immunological aspects of HIV-associated itchy folliculitis, in particular HIV-associated EF as well as current theories on pathogenesis and treatment. We suggest that HIV-associated EF is an autoimmune disease with the sebocyte or some constituent of sebum acting as the autoantigen.

Anti-CD34+ Fabs generated against hematopoietic stem cells in HIV-derived combinatorial immunoglobulin library suggest antigen-selected autoantibodies

Bone marrow suppression associated with HIV infection does not appear to be solely due to direct viral cytopathic effects. Autoantibodies may play a role in myelosuppression, however it is unclear whether autoantibodies produced in HIV infection represent a primary pathogenic process or merely reflect polyclonal B cell activation. To address these questions, we generated combinatorial immunoglobulin libraries using the pComb3 phagemid from an HIV+ individual with evidence of circulating autoantibodies. From one library, three anti-CD34 Fabs were identified using fresh CD34+ cells as antigenic targets by a method of phage subtraction. The anti-CD34 Fabs are specific by immunoblotting and Elisa and are of high affinity, with calculated Kds in the range of 10(-7) -10(-8) M. Nucleic acid sequencing revealed all three to be of the VH3 family and to have lambda light chains with some gene segments expressing little somatic mutation, while other segments were somatically mutated in patterns suggestive of antigen selection. These findings indicate that (1) A subset of HIV-associated anti-CD34 autoantibodies are monospecific and antigen-selected and are not merely a consequence of polyclonal B cell activation and elevated Ig levels in HIV. Autoreactivity in HIV therefore includes both polyspecific, low affinity antibodies as well as monospecific antigen-selected high affinity antibodies. (2) Although bone marrow suppression in HIV is likely to be multifactorial, autoantibodies to hematopoietic stem cells may contribute to its pathogenesis. (3) Library sampling of VH gene family rearrangements shows no evidence for under-representation of the VH3 family in the immune dysregulation of HIV infection. Phage subtraction is corroborated to be an effective means of identifying, cloning, and characterizing antibodies to hematopoietic differentiation antigens.

Can site-directed mutagenesis eliminate autoimmunity arising from molecular mimicry?

One proposed mechanism of pathogenic retroviral infection involves autoimmunity. Molecular mimicry may occur between viral and host proteins which share sequence homologies. Immune processing of antigenic peptides can result in the generation of cross-reactive antibodies capable of binding to host tissues. Thus, it appears the immune system can inadvertently initiate an attack upon the host due to genetic similarities between non-self and self. Site-directed mutagenesis is a tool of molecular biology often utilized to induce genetic changes in a microbe of interest. Since retroviral etiology may possess an autoimmune component, it seems plausible to utilize site-directed mutagenesis to genetically shape the retroviral genome. Retroviruses possess a DNA intermediate in their lifecycle, allowing the problem of retroviral infection to be addressed as a genetic disorder of the host. Detrimental autoimmune responses associated with retroviral pathology might be ameliorated by shaping the genetic source of their existence.

HIV type 1 envelope glycoprotein 120 carboxy-terminal peptide-induced human T cell lines selectively suppress heterogeneous proliferative T cell responses to soluble antigens

It has been proposed that the highly conserved human immunodeficiency virus type 1 (HIV-1) envelope gp120 carboxy-terminal sequence, TKAKRRVVEREKR (CT120), may represent a functional mimic of the human leukocyte antigen (HLA) class II DR beta-chain third hypervariable region (HVR3) sequence motif located at position 69-81. Presentation of this potentially pathogenic fragment by HLA class I and/or II molecules, in a manner analogous to the indirect pathway of allorecognition, may induce both widespread cellular activation and also break self-tolerance, resulting in the selective and progressive anti-self HLA class II-directed immune suppression, which is a central feature of HIV-1 infection and the associated acquired immune deficiency syndrome (AIDS). To investigate the functional role of the HIV-1 gp120 C-terminal fragment T cell lines (TCLs) were raised from three healthy HIV-1-seronegative subjects at low risk of HIV-1 exposure, by repeated stimulation with a short synthetic 13-mer CT120 peptide in vitro. Graded concentrations (10[3] to 5 x 10[4]) of CT120 TCLs suppressed the primary 6-day proliferation of autologous PBMCs in response to the soluble antigens tetanus toxoid (TT) and purified protein derivative (PPD). In contrast, CT120 TCLs demonstrated no suppressive effect on 3-day phytohemagglutinin (PHA), concanavalin A (ConA), and pokeweed mitogen (PWM) mitogenic responses. Fractionation of CT120 TCLs into highly purified CD4+ and CD8+ T cell subsets demonstrated that the CD8+ T cell fraction mediated the suppressor effector function. HLA restriction analysis revealed a complex pattern as both anti-HLA class II DR and anti-HLA class I (A, B, C) MAbs inhibited proliferation of oligoclonal CD8+ CT120 TCLs. Strategies aimed at specifically inhibiting such putative immunopathogenic HIV-1-encoded T cell epitopes may be an important consideration for development of future HIV-1 immunotherapy.

Molecular mimicry: can epitope mimicry induce autoimmune disease?

Mimicry of host antigens by infectious agents may induce cross-reactive autoimmune responses to epitopes within host proteins which, in susceptible individuals, may tip the balance of immunological response versus tolerance toward response and subsequently lead to autoimmune disease. Epitope mimicry may indeed be involved in the pathogenesis of several diseases such as post-viral myocarditis or Chagas disease, but for many other diseases in which it has been implicated, such as insulin-dependent diabetes mellitis or rheumatoid arthritis, convincing evidence is still lacking. Even if an epitope mimic can support a cross-reactive T or B cell response in vitro, its ability to induce an autoimmune disease in vivo will depend upon the appropriate presentation of the mimicked host antigen in the target tissue and, in the case of T cell mimics, the ability of the mimicking epitope to induce a proliferative rather than anergizing response upon engagement of the MHC-peptide complex with the T cell receptor. B cell presentation of mimicking foreign antigen to T cells is a possible mechanism for instigating an autoimmune response to self antigens that in turn can lead to autoimmune disease under particular conditions of antigen presentation, secondary signalling and effector cell repertoire. In this review evidence in support of epitope mimicry is examined in the light of the necessary immunological considerations of the theory.

The role of host immune responses in determining the outcome of HIV infection

The progression of disease following infection with human immunodeficiency virus (HIV) correlates with an activated immune system and would appear to depend to some degree on the immunogenetics of the host. Here, Michael Westby, Fabrizio Manca and Angus Dalgleish discuss the evidence for HLA determination of clinical outcome and the potential implications of a restricted T-cell receptor repertoire for pathogenesis.

Human immunodeficiency virus and the skin: selected controversies

Acquired immunodeficiency syndrome was first recognized as a new disease in 1981 because of the unusual association of Kaposi's sarcoma and Pneumocystis carinii pneumonia in young men. The skin remains one of the most important clinical markers for acquired immunodeficiency syndrome, now recognized as the end stage of infection with the human immunodeficiency virus (HIV). Indeed, an urticarial viral exanthem appearing during seroconversion may allow early identification of newly infected individuals who might benefit from administration of antiviral therapy during plasma viremia. The "asymptomatic HIV infection" is often accompanied by multiple skin complaints, which commonly include xerosis, pruritus, psoriasis/seborrheic dermatitis, and pruritic papular eruptions, the cause of which remains controversial. Psoriasis and Kaposi's sarcoma lesions share features including angiogenesis, dermal dendrocytes infected with HIV, and epidermal hyperproliferation, and are manifested by mice transgenic for HIV provirus or Tat-ltr. Changes in the immune system including T-cell function, antigen response, and shifting cytokine expression as well as a propensity for autoimmune reactions must underlie the skin immunodysfunction occurring in the setting of HIV infection. One of the most unsettling controversies suggested by in vitro data is that ultraviolet light, an effective therapy for HIV-related skin disorders, may actually activate the virus.

HIV-mediated B-lymphocyte activation and lymphomagenesis

Non-Hodgkin's (1ii)lymphoma is an AIDS-defining event in a significant percent of U.S. patients infected with the human immunodeficiency virus (HIV). Advances in anti-retroviral treatment and management of opportunistic infection have been accompanied by an increase in the incidence of these lymphomas. In the immunocompromised state of patients late in the course of HIV infection, these lymphomas represent a complication of HIV infection that is associated with an extremely poor prognosis. Currently, there is little understanding of the pathogenesis of HIV-associated lymphomas, which are nearly exclusively of B-cell origin. Experimental data do not support HIV infection in these lymphomas. While some lymphomas show evidence of EBV infection, the majority do not. Polyclonal B-cell hyperactivity during the early phases of HIV infection argues that chronic B-cell stimulation may be the major process predisposing B-cells in the HIV-infected individual to malignant transformation. The mechanism of this stimulation of normal B cells and its relationship to AIDS-associated lymphomas remain poorly understood. In this review, we will summarize current information on HIV-associated B lymphoma and then discuss our views on the association and regulation of HIV-related hyperactivity on the pathogenesis of this lymphoma.

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.

CD4 similarity to proteins of infectious agents in AIDS and their role in autoimmunity

Lymphocytotoxic autoimmunity (LA) is ubiquitous in AIDS. Its causes are unknown. We report that significant amino acid sequence similarities exist between the proteins of infectious organisms associated with AIDS and the CD4 protein of T-helper lymphocytes. These included: HIV, cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex viruses (HSV), Varicella Zoster virus (VZV), Escherichia coli, Mycobacteria, Mycoplasmas, Plasmodium, and Staphylococcus. It has been reported previously that HIV proteins have significant similarities with human class II MHC (HLA class II) proteins. Since CD4 and HLA class II proteins are chemically complementary, pairs of homologous antigens will also be complementary. It follows that concurrent infections with CD4 and HLA class II-homologous antigens will result in idiotype-antiidiotype antibody pairs that cannot distinguish 'self' from 'nonself', that acts as lymphocytotoxins, and form circulating immune complexes. Thus, combined HIV-CMV, HIV-EBV, HIV-HBV, HIV-mycoplasma, or other appropriate infectious pairs may suffice to trigger LA in AIDS.

Molecular mimicry in the pathogenesis of AIDS: the HIV/MHC/mycoplasma triangle

The immune defects characterizing infection with the human immunodeficiency virus (HIV) and culminating in the acquired immune deficiency syndrome (AIDS) are the result of a multifactorial disease process, components of which are the occurrence of autoimmune phenomena and opportunistic infection. In this discussion, the observation that both the HIV-1 gp 120 envelope and Mycoplasma genitalium adhesin proteins share an area of significant similarity with the CD4-binding site of the class II major histocompatibility complex (MHC) proteins is placed in this perspective and mechanisms by which interaction within this triad could contribute to the T-cell dysfunction, T-cell depletion, Th1-cell-->Th2-cell shift, B-cell proliferation, hyperglobulinemia and antigen-presenting cell dysfunction observed during the development of AIDS are proposed.

Intrathecal synthesis of anti-myelin basic protein IgG in HIV-1+ patients

Human immunodeficiency virus type 1 (HIV-1)-infected individuals frequently develop a broad spectrum of neurological syndromes, classified as HIV-1-associated cognitive/motor complex. Diffuse demyelination of hemispheric white matter is a commonly observed in HIV-1 infected brain, but the events leading to myelin destruction are still obscure. Since oligodendrocyte infection by HIV-1 is not proven as yet, myelin damage in HIV-1 infection may result from indirect mechanisms such as the excessive release of myelinotoxic substances or the triggering of autoimmune responses directed to myelin constituents. To verify the latter hypothesis, we searched for elevated anti-myelin basic protein (MBP) IgG levels in the cerebrospinal fluid (CSF) and serum of 25 patients with HIV-1 infection, 12 with multiple sclerosis (MS), and 9 with non-inflammatory neurological diseases (NIND). CSF, but not serum, anti-MBP IgG levels were more frequently elevated in HIV-1+ (16/25, 64%) than in MS (3/12, 25%) or NIND (0/9) patients. By using the anti-MBP IgG index, the anti-MBP IgG antibody specificity index (ASI), and the search for anti-MBP oligoclonal IgG, we ascertained that anti-MBP IgG were produced within the CNS in 13 of 25 (52%) HIV-1+, in 6 of 12 (50%) MS, and in none of NIND patients. The incidence of increased CSF anti-MBP IgG levels was higher among HIV-1+ patients at stage II-III (4/4, 100%) or at stage IV B (7/9, 78%) than among those at stage IV C-IV D (5/12, 42%). Although our data indicate that intrathecal anti-MBP IgG may occur early during HIV-1 infection and that they are more common in patients with HIV-1-associated cognitive/motor complex, the possible demyelinating role of these antibodies remains to be demonstrated.

Anti-lymphocyte antibodies in plasma of HIV-1-infected patients preferentially react with MHC class II-negative T cells and are linked to antibodies against gp41

It has previously been shown that HIV-infected patients develop anti-lymphocyte antibodies. The relationship between anti-lymphocyte antibodies and antibodies against different viral antigens is unknown, and it remains controversial whether some lymphocyte subpopulations are targeted preferentially. We have set out using three-colour flow cytometry to measure antibodies against different lymphocyte subsets. Staining with anti-human immunoglobulin and two MoAbs was performed to characterize the immunoglobulin load of different lymphocyte subsets. Comparison was done between patients' antibody reactivity against HIV-1 antigens and anti-lymphocyte antibodies. We were able to demonstrate the presence of anti-lymphocyte antibodies in approximately 75% of the HIV-infected patients (n = 78) (healthy controls were all negative). MHC class II-negative T cells showed a stronger reaction with anti-lymphocyte antibodies than B cells or MHC class II-positive T cells. Patients with antibodies against CD4 lymphocytes showed a significantly higher antibody reaction with the retroviral antigen gp41 than patients without these antibodies. An association between anti-lymphocyte antibodies and antibody reactivity against other HIV-1 antigens was not noticed. In conclusion, anti-lymphocyte antibodies in HIV-1-infected patients show a preferential reactivity with T cells which lack expression of MHC class II molecules. There is an increased antibody reactivity against gp41 in patients with anti-CD4+ T cell antibodies. The association hints at a specific origin of anti-lymphocyte antibodies in HIV-1-infected patients due to cross-reactivity with viral epitopes or network phenomena. These anti-CD4 cell antibodies could be of interest in the clinical course of HIV infection.

Characterization of human CD4+, HIV-SF2 Nef-specific T-cell clones for antigen-processing and presentation requirements and for cytotoxic activity

We have described previously the generation of seven HIV-SF2 Nef-specific, CD4+ T-cell clones, identification of epitopes within which are recognized by these clones, and the MHC alleles that restrict their responses. In this study, we have extended this characterization to include evaluation of antigen-processing and presentation requirements and cytotoxic activity. Clones were generated from five HIV-1 uninfected donors by in vitro stimulation of peripheral blood mononuclear cells with purified recombinant Nef1. In experiments with fixed cells, with the exception of two clones, recognition of Nef, but not Nef peptides, required processing. Also, at higher concentrations of antigen, the clones themselves were capable of presenting Nef peptides, but not soluble Nef. All clones had the ability to specifically lyse autologous, Epstein-Barr virus-transformed lines sensitized with Nef synthetic peptides, or, in some cases, soluble Nef. The cytotoxic activity mapped to the same epitopes identified for the proliferative response (a.a. 14-22, 47-53, 68-77, 70-77, 195-203 and 185-192) and was restricted by the same HLA class II molecules (DRw6, DQw7, DRw15(2), DR1 and DP5). Sensitization of the cytolytic clones with specific Nef peptides, but not soluble Nef, resulted in autolysis.

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.

Immunogenetics of chronic liver diseases

The genetic background of autoimmune diseases becomes more and more evident. Immunogenetics comprises the analysis of genes and their products located at the region 6p21 on the short arm of chromosome 6, which is also known as the major histocompatibility complex (MHC). MHC class I and II genes are highly polymorphic. The complement genes C2, C4A, C4B, and BF, which are also polymorphic, became known as MHC class III genes. In autoimmune hepatitis type 1, there is a dual association for white persons with either HLA-A1-B8-DR3 or HLA-DR4. In patients from Japan, autoimmune hepatitis type 1 is predominantly associated with HLA-DR4. This dual association is confirmed at the DNA level. Whereas only limited data are available for autoimmune hepatitis type 2, the association of primary biliary cirrhosis with HLA-DR8 is based on several studies. Primary sclerosing cholangitis is associated with HLA-B8-DR3 and -DR52a. This association was confirmed at the DNA level because of a significant increase of the DRB3*0101 allele. For DRB3*0101-negative individuals, a second association with DRB5*0101 (= DR2) was described. Further analysis of the hypervariable region of the HLA class II molecule indicates that lysine at position 71 is crucial for autoimmune hepatitis type 1 in white persons, whereas position 13 is important for people from Japan. In contrast, leucine at position 35 is important for patients with primary biliary cirrhosis, whereas leucine at position 38 is an important risk factor for primary sclerosing cholangitis. The MHC class III allele C4A-QO is significantly increased in autoimmune hepatitis type 1 and 2 and in primary biliary cirrhosis. Advances in immunogenetics will certainly increase our knowledge of the etiology and pathogenesis of immune-mediated liver diseases, which hopefully will lead to more specific therapeutic interventions.

Involvement of HIV nef protein in abnormal hematopoiesis in AIDS: in vitro study on bone marrow progenitor cells

In previous studies (1-4), we described disrupted hematopoiesis in long-term human bone marrow cultures infected with HIV. Conditioned medium (CM) from HIV-1 non-productively infected liquid cultures inhibits the proliferation of granulo-monocytic progenitor cells (CFU-GM) in clonogenic assays. A growth-inhibitory soluble factor was therefore suspected and we report here that this factor has been identified as the nef gene product. These nef-containing supernatants are specifically neutralized by anti-nef antibodies and recombinant nef has the same growth inhibitory properties. We used a nef-deficient virus to confirm that nef protein is responsible for the in vitro growth inhibition of CFU-GM.

Four cross-linked HIV Gag peptides prime the immune response to HIV proteins in mice

The functional help provided by four cross-linked synthetic peptides from HIV-1 Gag structural proteins was investigated in the mouse model. These peptides, selected upon non-self-criteria, are not predicted as T epitopes by classical prediction methods such as the Rothbard consensus or the amphipathy rule. Priming mice with these peptides allows the enhancement of the antibody response to HIV-1 Gag proteins (p55, p18, p24) given in the viral particle form. Furthermore, all of them also induce spleen and lymph node cells from primed mice to proliferate in vitro, in a MHC class II restricted context. This approach may help to identify relevant immunogenic viral epitopes that may be involved in a vaccinal strategy.

Does the HIV Nef protein mimic the MHC?

The sequence of the HIV Nef protein has no significant homology to other proteins in the SwissProt database, and experimental data concerning its function are sparse and contradictory. Using a novel protein sequence comparison method, we find similarities between different Nef sequences and the alpha chain of human MHC class I proteins. The possible biological implications of this finding are discussed.

Expression of human immunodeficiency virus type 1 Nef antigen on the surface of acutely and persistently infected human T cells

The authors have previously shown the role of human immunodeficiency virus type 1 (HIV-1) Nef protein as a growth inhibitor to CD4+ T lymphocytes. We now report that the Nef antigen is partly expressed on both acutely and persistently infected human T cells. To investigate the cell surface expression of the Nef antigen, murine monoclonal antibodies (mAbs) were prepared by immunization with a recombinant Nef protein. The recombinant Nef was expressed by a baculovirus expression system as a truncated Nef protein with 22 kDa containing the middle to the C-terminus. Three clones were found to produce mAbs with IgM isotype against Nef protein by ELISA with the same truncated Nef. All these mAbs reacted on immunoblotting with two forms of Nef, 25 kDa and 27 kDa, in an HIV-1-infected human T-cell line and with the 27 kDa Nef in retroviral vector-infected mouse fibroblasts expressing a full-length Nef protein. Membrane immunofluorescence and flow cytometry with these mAbs revealed the Nef antigen to be expressed, at least in part, on the surface of these cells. Thus, the cell-surface form of Nef might play an important role in the selective depletion of CD4+ cells in HIV-1 infection.

Analysis of human immunodeficiency virus type 1 nef gene sequences present in vivo

The nef genes of the human immunodeficiency viruses type 1 and 2 (HIV-1 and HIV-2) and the related simian immunodeficiency viruses (SIVs) encode a protein (Nef) whose role in virus replication and cytopathicity remains uncertain. As an attempt to elucidate the function of nef, we characterized the nucleotide and corresponding protein sequences of naturally occurring nef genes obtained from several HIV-1-infected individuals. A consensus Nef sequence was derived and used to identify several features that were highly conserved among the Nef sequences. These features included a nearly invariant myristylation signal, regions of sequence polymorphism and variable duplication, a region with an acidic charge, a (Pxx)4 repeat sequence, and a potential protein kinase C phosphorylation site. Clustering of premature stop codons at position 124 was noted in 6 of the 54 Nef sequences. Further analysis revealed four stretches of residues that were highly conserved not only among the patient-derived HIV-1 Nef sequences, but also among the Nef sequences of HIV-2 and the SIVs, suggesting that Nef proteins expressed by these retroviruses are functionally equivalent. The "Nef-defining" sequences were used to evaluate the sequence alignments of known proteins reported to share sequence similarity with Nef sequences and to conduct additional computer-based searches for similar protein sequences. A gene encoding the consensus Nef sequence was also generated. This gene encodes a full-length Nef protein that should be a valuable tool in further studies of Nef function.

Salivary autoantibodies in HIV-associated salivary gland disease

A subset of HIV-positive patients develops salivary gland disease (HIV-SGD), characterized by salivary gland enlargement and/or decreased salivary flow. While clinical symptoms are similar to Sjögren's syndrome (SS), patients with HIV-SGD lack circulating anti-SS-A/Ro and anti-SS-B/La. Occasionally, SS patients lacking circulating anti-SS-A/Ro and anti-SS-B/La have these antibodies in their saliva. Salivas from 11 patients with HIV-SGD, 13 HIV+ patients without HIV-SGD, 14 HIV-negative men controls, and 11 patients with SS were screened for autoantibodies. Five HIV-SGD salivas had antibodies recognizing the cytoplasm of a salivary cell line. No HIV+ controls showed reactivity. Ten of 11 SS patients had salivary autoantibodies, and one HIV-negative control was positive for them. Salivary anti-SS-A/Ro was present in 8/11 SS patients, and 7 also contained anti-SS-B/La. No HIV-SGD salivary samples had these specific autoantibodies. These findings suggest that while glandular polyclonal expansion occurs in both HIV-SGD and SS, different autoantibodies are produced.

Antibodies to retroviral proteins in autoimmune connective tissue disease. Relation to clinical manifestations and ribonucleoprotein autoantibodies

OBJECTIVE

To study the relationship between antibodies that recognize human retroviral proteins and the presence of clinical features and ribonucleoprotein antibodies in patients with autoimmune connective tissue diseases (CTDs).

METHODS

Antibodies against native human immunodeficiency virus type 1 (HIV-1) and human T cell leukemia/lymphoma virus type I, recombinant HIV-1 Nef protein, and ribonucleoprotein antigens were determined by immunoblot of sera from 65 prospectively studied patients with definite or suspected CTDs of autoimmune type.

RESULTS

Antibodies to retroviral proteins (ARP), most frequently to HIV Gag proteins p55 and p24, were found in 64% of 22 patients with systemic lupus erythematosus (SLE), in 63% of 8 patients with discoid LE (DLE), in 75% of 8 patients with mixed connective tissue disease (MCTD), and in 26% of 19 individuals with chronic biologically false-positive (CBFP) seroreactions, but not in 8 patients with subacute cutaneous lupus erythematosus. No clear correlation of ARP with antibodies to any specific small nuclear RNP antigen was observed. The most striking finding was that recurrent infections, both in LE patients and in those with CBFP reactions and widespread, acral discoid skin lesions, occurred significantly more often in ARP-positive patients.

CONCLUSION

The occurrence of antibodies reacting with human retroviral proteins is associated with severe skin lesions and recurrent infections in SLE, DLE, and MCTD patients, and with a disposition toward developing systemic disease in CBFP reactors.

A gp120 HIV peptide with high similarity to HLA class II beta chains enhances PPD-specific and autoreactive T cell activation

The recent report that anti-gp120 antibodies can be induced by allogeneic stimuli in experimental animals in the absence of HIV, has focused attention on the structural similarities between gp120 and MHC. Here we report that some HIV+ individuals develop antibodies which similarly react with the gp120 HIV sequence (aa 254-263) and with the HLA-DR beta chains (aa 142-151). As these two peptides share a high level of similarity, we have investigated the role of this gp120 region on HLA class II mediated T cell recognition. The synthetic peptide corresponding to the gp120 HIV sequence aa 254-263 has been tested on T cell line (TCL) activation. Both the PPD-specific and the self-HLA reactive TCL proliferation increased in the presence of this peptide. Prepulsing experiments indicate that this enhancing effect carried out by HIV peptide is exerted at the level of antigen presentation. Moreover, the specificity of this interaction is supported by the fact that a MoAb specific for this HIV peptide blocked the autoreactive TCL proliferation, similarly to the inhibition carried out by anticlass II antibody. These data support the hypothesis that the functional homology between the HIV peptide and the HLA beta chain described may be involved in the pathogenesis of AIDS.

The blood group antigen-related glycoepitopes: key structural determinants in immunogenesis and AIDS pathogenesis

This overview will focus on the functional and pathophysiological aspects of blood group antigen (BGA)-related glycodeterminants with regard to immunogenesis and AIDS pathogenesis. It has been postulated that in a broad range of histogenetically different tissues and organs, BGA-related glycoepitopes are expressed on the cell surface at definite stages of cell differentiation. These glycoepitopes are expressed during embryogenesis, organogenesis, tissue repair, regeneration, remodelling and maturation when 'sorting-out' of one homotypic cell population from a heterotypic assemblage of cells occurs (1). In this event, the BGA-related glycoepitopes, if being expressed on the cell surface, play roles of key structural determinants in cell-cell recognition, association and aggregation. This mechanism will be discussed in relation to immunogenesis with regard to antigen presentation, self-non-self discrimination, and positive and negative selection during thymic education. It is postulated that the appearance of BGA-related glycoepitopes on the cell membrane is a consequence of the association of major histocompatibility complex antigens (MHC) and peptides, with the subsequent elimination of cells carrying a high density of BGA-related glycoepitopes on their surface. After human immunodeficiency virus (HIV) glycoproteins are glycosylated by host cell glycosyltransferases, the virus may use the BGA-related glycodeterminants as ligands and/or receptors for expansion to a spectrum of target cells during AIDS development and generalization of the infection throughout the body. We will review the experimental evidence that supports the concept that HIV uses an alternative to the gp120/CD4 ligand/receptor system, and that the alternative mechanism is probably carbohydrate-mediated in nature.

Antibodies to MHC class II peptides are present in HIV-1-positive sera

Seventy-five per cent of sera from HIV-1-infected individuals bind to the human B-lymphoma cells bearing the major histocompatibility class II molecule in enzyme-linked immunosorbent assay (ELISA). The binding is caused by the antibodies against the class II molecule present in the serum samples which prevent the interaction of murine anti-HLA.DR monoclonal antibody with B lymphoma in FACS analysis. The three highly conserved amino acid sequences in alpha- and beta-chains of the class II molecule and three homologous fragments in HIV-1 gp120 and gp41 were identified by computer search and synthesized. Using these peptides it was demonstrated that 28-48% of HIV-positive sera contain antibodies that cross-react with the peptide of HIV-1 origin and with the peptide from the class II molecule as well.

Expression and cellular localization of the Nef protein from human immunodeficiency virus-1 in stably transfected B-cells

Nef protein, encoded by the regulatory nef gene of human immunodeficiency virus type 1 (HIV-1), was expressed in the B-cell line Raji. The cells were stably transfected with plasmids containing the nef transcriptional cassette. They expressed Nef with an Mr of 27,000; the yield could be augmented by incubation with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate. The intracellular localization of Nef was analyzed applying immunofluorescence microscopy using a confocal laser scanning microscope. The antigen was stained with a monoclonal antibody directed against the N-terminal part of Nef. The experiments revealed that in non-dividing cells Nef is present both in the cytoplasm and the nucleus while in dividing cells the viral protein is present in the cytoplasm and at the nuclear membrane.

The blood group antigens (BGA)-related glycoepitopes. A key structural determinant in immunogenesis and cancer pathogenesis

This overview has been focused on the functional and pathophysiological aspects of blood group antigens (BGA)-related glycodeterminants. It has been postulated that in a broad range of histogenetically different tissues and organs BGA-related glycoepitopes are expressed on the cell surface at definite stages of cell differentiation during embryogenesis, organogenesis, tissue repair, regeneration, remodeling and maturation when 'sorting-out' behaviour of one homotypic cell population from heterotypic assemblage of cells occurs. In this event the BGA-related glycoepitopes, if being expressed on the cell surface, play a role of key structural determinants in cell-cell recognition, association and aggregation. This mechanisms has been discussed in relation to immunogenesis regarding of antigen presentation, self-non-self discrimination, positive and negative selection during thymic education. It is postulated that the appearance of the BGA-related glycoepitopes on the cell membrane is a consequence of the association of MHC and peptides, with subsequent elimination of cells carring high density of BGA-related glycoepitopes on their surface. In cancer it has been considered as a key mechanism of phenotypic divergence of tumor cells, immunoselection, tumor progression and metastasis.

Anti-HIV and anti-anti-MHC antibodies in alloimmune and autoimmune mice

Alloimmune mice (mice that have been exposed to cells from another murine strain) were shown to make antibodies against gp120 and p24 of human immunodeficiency virus (HIV), and mice of the autoimmune strains MRL-lpr/lpr and MRL-(+)/+ made antibodies against gp120. This is surprising because the mice were not exposed to HIV. Furthermore, anti-anti-MHC antibodies (molecules that have shapes similar to those of major histocompatibility complex molecules) were detected in both alloimmune sera and MRL mice. These results are discussed in the context of a possible role for allogeneic stimuli in the pathogenesis of acquired immunodeficiency syndrome, as suggested by an idiotypic network model.

Identification of a major human immunodeficiency virus-1 reverse transcriptase epitope recognized by mouse CD4+ T lymphocytes

Delineation of major T helper cell recognition sites of human immunodeficiency virus (HIV-1) proteins represents one important step in the design of an efficient acquired immune deficiency syndrome (AIDS) vaccine. Towards this end, we have explored the immunogenicity of HIV-1BRU proteins in the mouse model. Preliminary experiments revealed that inbred mice primed with whole inactivated HIV-1 developed strong CD4+ T cell proliferative responses to a variety of recombinant viral proteins including reverse transcriptase (RT). To characterize further the mouse T cell responses to this protein, several Ad- or Ed-restricted T hybridoma cells (THC) were established from BALB/c or DBA/2 mice. These THC were tested for their capacity to recognize a series of 15-mer synthetic overlapping peptides spanning three segments of HIV-1 RT that had been preselected on the basis of either alpha-helicity, amphipaticity, and/or for containing rare amino acid sequence patterns. Peptides corresponding to a C-terminal region (residues 528-560) of RT were recognized by several of the THC established from RT-primed mice. Furthermore, a non-alpha-helical peptide from this region (A3, 528-543) was capable of priming mice with different H-2 haplotypes for both peptide A3 and native RT CD4+ T cell recognition. In addition to the recently identified RT determinant 203-219 capable of triggering both mouse and human CD8+ CTL, the present results identify a good candidate for an immunodominant RT epitope capable of eliciting RT-specific T helper cell responses.

An idiotypic network model of AIDS immunopathogenesis

Considerations from a network theory of the immune system suggest that human immunodeficiency virus and allogeneic stimuli may act synergistically to cause AIDS. The immune responses to these stimuli include two components that are directed against each other. In some AIDS risk groups other antigens that mimic major histocompatibility complex antigens may substitute for allogeneic stimuli. Implications for the prevention of AIDS are discussed.

Epitopes of the HIV-1-negative factor (nef) reactive with murine monoclonal antibodies and human HIV-1-positive sera

Murine monoclonal antibodies (MAbs) raised against a recombinant nef protein fragment of human immunodeficiency virus type 1 (HIV-1) strain BH10 were characterized by an epitope mapping system using overlapping decapeptides. Four different immunogenic regions were identified. Ten human HIV-1-positive sera were tested in the same epitope mapping system, seven of these were reactive with four immunogenic regions. Two of the nef-specific epitopes recognized by human sera overlapped with the epitopes defined by the murine monoclonal antibodies. The reactivity of the monoclonal antibodies with the recombinant nef protein and with infected and uninfected cells were investigated in a variety of test systems. The results are discussed with respect to homologous regions of nef and cellular proteins.