Repression of MHC determinants in HIV infection

HIV infects CD4(+) macrophages and lymphocytes. Before the development of AIDS, HIV weakens the immune system in part by blocking antigen processing and presentation via major histocompatibility complex (MHC) molecules. In this report, we discuss how HIV escapes the immune surveillance by MHC II molecules.     

Leukocyte migration inhibitory factor (LIF) to sperm from autoimmune men in infertile couples

Leukocyte migration inhibitory factor (LIF) is produced by lymphocytes with receptors specific to sensitizing antigens. This principle was used to detect possible antigenic differences between sperm of autoimmune and nonautoimmune men. Sixteen fertile and 91 infertile couples were screened for cytotoxic and hemagglutinating antibodies to sperm from their husbands and controls. Their lymphocytes were tested for the production of LIF to sperm extracts and seminal plasma from the husbands and controls by a direct leukocyte migration inhibition assay. Twenty-nine of 35 men producing LIF to sperm and/or seminal plasma were positive for sperm antibodies (p = 0.0004, vs sperm antibody-negative controls). Twenty-three of 29 wives with LIF production had sperm-autoimmune husbands (p = 0.04). Leukocyte migration was significantly inhibited in sperm-autoimmune men by autologous sperm extracts and seminal plasma in contrast to control sperm extracts and seminal plasma (p = 0.0006 and 0.001, respectively). The wives of autoimmune men had significantly higher LIF responses to their husbands' sperm extracts than to other antigens (p = 0.02). Men with cytotoxic antibodies in their seminal plasma produced LIF to autologous sperm (p = 0.001). It is suggested that certain sperm and seminal plasma antigens of autoimmune men may lead to specific humoral and cell-mediated immune responses in both partners.     

Distribution of antibodies against denatured collagen in AIDS risk groups and homosexual AIDS patients suggests a link between autoimmunity and the immunopathogenesis of AIDS

Autoimmunity often precedes the onset of AIDS-related complex or AIDS, and a number of autoantibodies have been described in AIDS patients and persons at risk for AIDS. The presence of such antibodies provokes speculation that autoimmunity is a component of AIDS pathogenesis. We report evidence of an autoantibody (anticollagen) common to all homosexual AIDS patients studied. High titer serum reactivity against collagen was detected in all homosexual AIDS patients, and in HIV+ homosexuals (66%), HIV+ i.v. drug users (38%) HIV- homosexuals (32%), HIV+ transfusion recipients (22%), and HIV+ hemophiliacs (13%), but not in HIV- i.v. drug users, HIV- transfusion recipients, HIV- hemophiliacs, rheumatoid arthritis patients, or controls. Anticollagen reactivity does not correlate with serum IgG levels, so it is not merely a reflection of polyclonal B-cell activation. Titration of anticollagen positive sera typically revealed anticollagen antibody titers 100 times those of normal sera. Affinity purification and immunoblot analysis confirmed the antibody nature of the anticollagen reactivity. The anticollagen antibodies react preferentially with primary determinants of types I and III collagen revealed after heat denaturation. Similar antibodies occur infrequently in rheumatoid arthritis patients, more often on SLE, and frequently in graft vs host disease and lepromatous leprosy. Levels of anticollagen activity in HIV+ i.v. drug users and transfusion recipients correlate with serum beta 2-microglobulin levels, suggesting that those persons with anticollagen antibodies are at greater risk of developing AIDS. This correlation, the fact that anticollagen antibodies occurred in all homosexual AIDS patients tested, and the occurrence of antibodies against denatured collagen in immune disorders with features similar to AIDS suggest these antibodies may be related to disease progression. The association of anticollagen autoantibodies with AIDS and certain other infections and immune disorders may reflect common immunopathogenic features in the etiology of these disorders.     

Mucosal model of genital immunization in male rhesus macaques with a recombinant simian immunodeficiency virus p27 antigen.

Human immunodeficiency virus (HIV) can be transmitted through infected seminal fluid or vaginal or rectal secretions during heterosexual or homosexual intercourse. To prevent mucosal transmission and spread to the regional lymph nodes, an effective vaccine may need to stimulate immune responses at the genitourinary mucosa. In this study, we have developed a mucosal model of genital immunization in male rhesus macaques, by topical urethral immunization with recombinant simian immunodeficiency virus p27gag, expressed as a hybrid Ty virus-like particle (Ty-VLP) and covalently linked to cholera toxin B subunit. This treatment was augmented by oral immunization with the same vaccine but with added killed cholera vibrios. Polymeric secretory immunoglobulin A (sIgA) and IgG antibodies to p27 were induced in urethral secretions, urine, and seminal fluid. This raises the possibility that the antibodies may function as a primary mucosal defense barrier against SIV (HIV) infection. The regional lymph nodes which constitute the genital-associated lymphoid tissue contained p27-specific CD4+ proliferative and helper T cells for antibody synthesis by B cells, which may function as a secondary immune barrier to infection. Blood and splenic lymphocytes also showed p27-sensitized CD4+ T cells and B cells in addition to serum IgG and IgA p27-specific antibodies; this constitutes a third level of immunity against dissemination of the virus. A comparison of genito-oral with recto-oral and intramuscular routes of immunization suggests that only genito-oral immunization elicits specific sIgA and IgG antibodies in the urine, urethra, and seminal fluid. Both genito-oral and recto-oral immunizations induced T-cell and B-cell immune responses in regional lymph nodes, with preferential IgA antibody synthesis. The mucosal route of immunization may prevent not only virus transmission through the genital mucosa but also dissemination and latency of the virus in the draining lymph nodes.     

A single injection of recombinant measles virus vaccines expressing human immunodeficiency virus (HIV) type 1 clade B envelope glycoproteins induces neutralizing antibodies and cellular immune responses to HIV

The anchored and secreted forms of the human immunodeficiency virus type 1 (HIV-1) 89.6 envelope glycoprotein, either complete or after deletion of the V3 loop, were expressed in a cloned attenuated measles virus (MV) vector. The recombinant viruses grew as efficiently as the parental virus and expressed high levels of the HIV protein. Expression was stable during serial passages. The immunogenicity of these recombinant vectors was tested in mice susceptible to MV and in macaques. High titers of antibodies to both MV and HIV-Env were obtained after a single injection in susceptible mice. These antibodies neutralized homologous SHIV89.6p virus, as well as several heterologous HIV-1 primary isolates. A gp160 mutant in which the V3 loop was deleted induced antibodies that neutralized heterologous viruses more efficiently than antibodies induced by the native envelope protein. A high level of CD8+ and CD4+ cells specific for HIV gp120 was also detected in MV-susceptible mice. Furthermore, recombinant MV was able to raise immune responses against HIV in mice and macaques with a preexisting anti-MV immunity. Therefore, recombinant MV vaccines inducing anti-HIV neutralizing antibodies and specific T lymphocytes responses deserve to be tested as a candidate AIDS vaccine.     

New insights in antigen processing and epitope selection: development of novel immunotherapeutic strategies for cancer, autoimmunity and infectious diseases

Current evidence suggests that MHC class II-restricted CD4+ T-cells play a crucial role in orchestrating host immune responses against cancer as well as autoimmune and infectious diseases. Antigens must be processed within endosomal and lysosomal compartments of antigen presenting cells (APC) before binding to MHC class II molecules for display to T-cells. Only a limited number of processed peptides termed immunodominant are selected for display by MHC class II molecules and prove capable of inducing strong T-cell responses. Thus processing reactions within APC are of central importance for the development of effective vaccines as they modulate the number of peptide: class II complexes by enhancing or disrupting epitope formation and display. Studies suggest that there are substantial gaps in our knowledge of how antigen processing and presentation by APC regulates epitope selection and immunodominance in disease situations. Here we describe new insights in antigen processing and epitope selection with relevance to immunotherapeutic strategies for cancer, autoimmunity and infectious diseases.     

Cross-presentation in viral immunity and self-tolerance

T lymphocytes recognize peptide antigens presented by class I and class II molecules encoded by the major histocompatibility complex (MHC). Classical antigen-presentation studies showed that MHC class I molecules present peptides derived from proteins synthesized within the cell, whereas MHC class II molecules present exogenous proteins captured from the environment. Emerging evidence indicates, however, that dendritic cells have a specialized capacity to process exogenous antigens into the MHC class I pathway. This function, known as cross-presentation, provides the immune system with an important mechanism for generating immunity to viruses and tolerance to self.     

Genetic basis of HIV-1 resistance and susceptibility: an approach to understand correlation between human genes and HIV-1 infection

HIV infection is the serious medical and public health issue of present generation. By 2005, it has already infected a cumulative total of more than sixty million people worldwide and the number of HIV positive cases are rising day by day. India is currently estimated to have about 5.1 million infected persons with HIV-1 or AIDS (second only to South Africa) and this number could increase to 24 million in the next ten years. This pandemic situation of the AIDS stimulated a plethora of longitudinal cohort studies which are designed to document medical heterogeneity as well as to mitigate the factors that regulate the HIV-1 infection, disease progression and the immune defenses. In recent years these genetic studies have led to the discovery of various MHC and non MHC encoded genes, which directly or indirectly influence the susceptibility and resistance to HIV infection and AIDS. These genes and their mutated forms and their products which play a major role in determining the susceptibility or resistance to HIV-1 infection and AIDS. These genes have been categorized into MHC or non MHC encoded genes. The MHC encoded genes which determine HIV resistance or susceptibility are HLA-B57, HLA-B58, HLA-B27, HLA-Bw4 and HLA-A11 in Southeast Asians. On the other hand, non MHC encoded genes are CCR5, CCR2, RANTES, CXCL12, CXCR6, CCL3L1, Interleukin-10 (IL-10), and interferon gamma. The site specific mutations in these genes determine the susceptibility or resistance to HIV-1 infection and AIDS. In future the study of host genes in relation to HIV-1 infection may provide the researchers to develop newer chemotherapeutic approaches to prevent or cure HIV-1 infection effectively.     

CD4-like molecules in human sperm

The expression of a molecule recognized by CD4 monoclonal antibodies was investigated on human sperm using immunolabelling, biochemical and immunochemical methods. Flow cytometry detected a significant fluorescence signal. SDS-PAGE analysis and Western blotting identified a molecule of 60 kDa, consistent with a CD4-like structure as confirmed after selective immunoseparation. Additional bands reacting with anti-CD4 were found in sperm extracts (73 kDa) and seminal fluid (90 kDa). These data indicate that sperm express a molecule similar to the receptor for HIV described on mononuclear cells.     

The integrated HIV-1 provirus in patient sperm chromosome and its transfer into the early embryo by fertilization

Complete understanding of the route of HIV-1 transmission is an important prerequisite for curbing the HIV/AIDS pandemic. So far, the known routes of HIV-1 transmission include sexual contact, needle sharing, puncture, transfusion and mother-to-child transmission. Whether HIV can be vertically transmitted from human sperm to embryo by fertilization is largely undetermined. Direct research on embryo derived from infected human sperm and healthy human ova have been difficult because of ethical issues and problems in the collection of ova. However, the use of inter-specific in vitro fertilization (IVF) between human sperm and hamster ova can avoid both of these problems. Combined with molecular, cytogenetical and immunological techniques such as the preparation of human sperm chromosomes, fluorescent in situ hybridization (FISH), and immunofluorescence assay (IFA), this study mainly explored whether any integrated HIV provirus were present in the chromosomes of infected patients' sperm, and whether that provirus could be transferred into early embryos by fertilization and maintain its function of replication and expression. Evidence showed that HIV-1 nucleic acid was present in the spermatozoa of HIV/AIDS patients, that HIV-1 provirus is present on the patient sperm chromosome, that the integrated provirus could be transferred into early embryo chromosomally integrated by fertilization, and that it could replicate alongside the embryonic genome and subsequently express its protein in the embryo. These findings indicate the possibility of vertical transmission of HIV-1 from the sperm genome to the embryonic genome by fertilization. This study also offers a platform for the research into this new mode of transmission for other viruses, especially sexually transmitted viruses.     

Cross-reactivity between human and murine lymphocyte antigens: III. Reactivity of H-2 allo- and xenoantisera with human lymphoid cells

H-2 alloantisera and antimouse lymphocyte xenoantisera react with 14%–100% of human lymphocytes from a panel of at least 80 unrelated people. Population and family studies did not reveal HL-A specificity of such lymphocytotoxic antibodies but indicated that the antibodies are directed against polymorphic antigenic determinants inherited in association with HL-A antigens. H-2 allo- and xenoantisera absorbed with human lymphoid cells and a panel of platelets bearing all the known HL-A specificities were still cytolytic when tested against murine lymphocytes, suggesting that only a small proportion of the heterogeneous population of H-2 antibodies react with human lymphocytes. On the other hand, HL-A alloantisera could be absorbed by lymphocytes from certain murine strains. These results suggest that the crossreactivity between human and murine lymphocytes is caused by antigens common to several HL-A (or H-2) types or by antigens linked to HL-A but not identical with them.     

A murine CD4-, CD8- T cell receptor-gamma delta T lymphocyte clone specific for herpes simplex virus glycoprotein I.

The role of TCR-gamma delta T lymphocytes in immune responses is currently not well understood. TCR-gamma delta cells have a limited repertoire suggesting that TCR-gamma delta T a limited number of evolutionarily conserved Ag such as nonpolymorphic MHC and heat shock proteins. TCR-gamma delta T lymphocytes appear in enhanced numbers in skin lesions produced by Mycobacterium leprae and in the synovial fluid of joints affected by rheumatoid arthritis, raising the possibility that this subset of T lymphocytes may play a role in control of infectious processes and in autoimmune diseases. We report the identification of a TCR-gamma delta T cell clone isolated from a HSV-infected mouse that recognizes glycoprotein I of HSV type 1. Clone recognition of glycoprotein I does not appear to require the expression of MHC class I or class II gene products. These data suggest that TCR-gamma delta lymphocytes may play an important role in the immune response to viral infections.     

Different effects of paternal trans-generational immune priming on survival and immunity in step and genetic offspring

Paternal trans-generational immune priming, whereby fathers provide immune protection to offspring, has been demonstrated in the red flour beetle Tribolium castaneum exposed to the insect pathogen Bacillus thuringiensis. It is currently unclear how such protection is transferred, as in contrast to mothers, fathers do not directly provide offspring with a large amount of substances. In addition to sperm, male flour beetles transfer seminal fluids in a spermatophore to females during copulation. Depending on whether paternal trans-generational immune priming is mediated by sperm or seminal fluids, it is expected to either affect only the genetic offspring of a male, or also their step offspring that are sired by another male. We therefore conducted a double-mating experiment and found that only the genetic offspring of an immune primed male show enhanced survival upon bacterial challenge, while phenoloxidase activity, an important insect immune trait, and the expression of the immune receptor PGRP were increased in all offspring. This indicates that information leading to enhanced survival upon pathogen exposure is transferred via sperm, and thus potentially constitutes an epigenetic effect, whereas substances transferred with the seminal fluid could have an additional influence on offspring immune traits and immunological alertness.     

Simian immunodeficiency virus induces expression of class II major histocompatibility complex structures on infected target cells in vitro

The human immunodeficiency virus (HIV) and the closely related simian immunodeficiency virus (SIV) induce profound immune dysfunction in primate species. The present studies show that cell populations infected in vitro with SIV exhibit increases in major histocompatibility complex (MHC) class II antigen expression. Cell lines chronically infected with both the monkey and human viruses express substantially more MHC class II but not more lineage-restricted or activation antigens on their membranes than do uninfected cell lines. Furthermore, 2'-deoxy-5-iodouridine increased MHC class II antigen expression on SIV-infected cell lines in parallel with increased expression of viral antigens. MHC class II induction does not appear to be mediated through the production of a soluble factor, such as gamma interferon, by SIV-infected cells. Interestingly, studies of the kinetics of antigen expression by cell lines after SIV infection indicate that the induction of MHC class II structures is a late event. Immunoelectron microscopy revealed that MHC class II antigen is expressed not only on the surfaces of the SIV-infected cells but also on the envelope of virus particles derived from those cells. MHC antigen expression on virus-infected cells and the expression of those determinants by the virus may play a role in the pathogenesis of acquired immunodeficiency syndrome and the autoimmune abnormalities observed in HIV-infected individuals.     

Function of the CD4 and CD8 molecules on human cytotoxic T lymphocytes: regulation of T cell triggering

The function of the T cell differentiation antigens CD4 (Leu-3/T4) and CD8 (Leu-2/T8) on human cytotoxic T lymphocytes (CTL) is presently seen only in conjugate formation between CTL and target cell via class II or class I MHC antigens rather than in the later killing steps. In this study, human CD4+ and CD8+ CTL clones were used to investigate the effects of monoclonal antibodies against these differentiation antigens on nonspecific triggering of cytotoxicity. Cytotoxicity was induced either by antibodies against the CD3 (T3) antigen or by the lectins Con A and PHA. Anti-CD4 or anti-CD8 antibodies specifically inhibited all types of cytotoxicity of CD4+ or CD8+ CTL, respectively, regardless of the specificity of the CTL for class I or class II HLA antigens and regardless of whether target cells expressed class I or class II antigens. These results are incompatible with an exclusive role of the CD4 and CD8 molecules in MHC class recognition and are discussed with respect to a function as negative signal receptors for these molecules on CTL.     

Identification of a potent synthetic HIV1 immunogen compromising gag-P24 tandem T- and B-cell epitopes.

Recent studies indicate that the gag gene products may play a crucial role in the immune response against HIV infection since clinical progression to AIDS is associated with a reduction in the level of circulating antibodies to gag p24 and antibodies raised against p17 peptide can inhibit HIV1 infection in vitro. Using conventional structure prediction algorithms for T-cell and B-cell epitopes, we have selected and chemically synthesized several gag peptides. In particular, an unconjugated HIV1-p24 peptide containing both B- and T-cell epitopes in tandem plus Freund's adjuvant induced a strong antibody response in both mice and rabbits against p24 and its precursor p55 as judged by immunoblotting. In addition, the peptide presented in the appropriate MHC context was shown to be highly stimulatory for p24 specific murine T-cell clones.     

Cytokine/Chemokine HLDA8 Workshop panel report: analysis of receptors on lymphocytes from cord blood, normal and asthmatic subjects, and HIV positive patients

Chemokines and cytokines are involved in many processes, both physiological and pathological, particularly the recruitment, differentiation, activation, and proliferation of immune cells taking part in ontogenesis, inflammation, and cancer. It was assumed that chemokines and cytokines receptors are expressed in a regulated manner by human lymphocytes during ontogeny and later on, under the environmental stimulation of antigens they contribute to organogenesis, angiogenesis, and tissue remodeling, as well as modulating leukocyte effector functions. Using monoclonal antibodies classified by the Cytokine/Chemokine section of the 8th International Workshop on Human Leukocyte Differentiation Antigens, we analyzed human lymphocytes in blood samples drawn from the umbilical cord, normal adults, allergic and non-allergic asthma patients, HIV infected, and AIDS positive subjects. The main differences noted between adult and cord blood lymphocytes were related to CCR7 and CXCR4 receptors, which were more strongly expressed on cord blood lymphocytes, confirming the important role of these chemokines during development of the immune system. As with the HIV, CXCR4, and CCR5 co-receptors, we found no differences in CXCR4 expression between HIV and AIDS patients. However CCR5 was more strongly expressed in AIDS patients, which is likely to be associated with the evolution of disease. Further studies are needed to gain a better understanding of the functions of these molecules in the underlying pathogenesis of many diseases and to probe the use of the chemokine receptors as targets for therapeutic intervention.     

Seminal fluid induces leukocyte recruitment and cytokine and chemokine mRNA expression in the human cervix after coitus

In mice, seminal fluid elicits an inflammation-like response in the female genital tract that activates immune adaptations to advance the likelihood of conception and pregnancy. In this study, we examined whether similar changes in leukocyte and cytokine parameters occur in the human cervix in response to the male partner's seminal fluid. After a period of abstinence in proven-fertile women, duplicate sets of biopsies were taken from the ectocervix in the periovulatory period and again 48 h later, 12 h after unprotected vaginal coitus, vaginal coitus with use of a condom, or no coitus. A substantial influx of CD45(+) cells mainly comprising CD14(+) macrophages and CD1a(+) dendritic cells expressing CD11a and MHC class II was evident in both the stratified epithelium and deeper stromal tissue after coitus. CD3(+)CD8(+)CD45RO(+) T cells were also abundant and increased after coitus. Leukocyte recruitment did not occur without coitus or with condom-protected coitus. An accompanying increase in CSF2, IL6, IL8, and IL1A expression was detected by quantitative RT-PCR, and microarray analysis showed genes linked with inflammation, immune response, and related pathways are induced by seminal fluid in cervical tissues. We conclude that seminal fluid introduced at intercourse elicits expression of proinflammatory cytokines and chemokines, and a robust recruitment of macrophages, dendritic cells, and memory T cells. The leukocyte and cytokine environment induced in the cervix by seminal fluid appears competent to initiate adaptations in the female immune response that promote fertility. This response is also relevant to transmission of sexually transmitted pathogens and potentially, susceptibility to cervical metaplasia.     

Primate‐specific regulation of natural killer cells

Natural killer (NK) cells are circulating lymphocytes that function in innate immunity and placental reproduction. Regulating both development and function of NK cells is an array of variable and conserved receptors that interact with major histocompatibility complex (MHC) class I molecules. Families of lectin‐like and immunoglobulin‐like receptors are determined by genes in the natural killer complex (NKC) and leukocyte receptor complex (LRC), respectively. As a consequence of the strong, varying pressures on the immune and reproductive systems, NK cell receptors and their MHC class I ligands evolve rapidly, are highly diverse and exhibit dramatic species‐specific differences. The variable, polymorphic family of killer cell immunoglobulin‐like receptors (KIR) that regulate human NK cell development and function arose recently, from a single‐copy gene during the evolution of simian primates. Our studies of KIR and MHC class I genes in representative species show how these two unlinked but functionally intertwined genetic complexes have co‐evolved. In humans, combinations of KIR and HLA class I factors are associated with infectious diseases, including HIV/AIDS, autoimmunity, reproductive success and the outcome of therapeutic transplantation. The extraordinary, and unanticipated, divergence of human NK cell receptors and MHC class I ligands from their mouse counterparts can in part explain the difficulties experienced in finding informative mouse models for human diseases. Non‐human primate models have far greater potential, but to realize their promise will first require more complete definition of the genetics and function of KIR and MHC variation in non‐human primate species, at a level comparable to that achieved for the human species.     

AIDS and human lymphocytes

HIV infection is no doubt the primary cause of AIDS. But the relationship between HIV and its host lymphocytes is fairly complicated. It has become clear that the host range of the viruses varies according to the clinical stage of the patients from whom viruses were isolated. Besides, the cause or mechanism of cell killing by HIV infection is not well-known. The density of CD4 molecules on the cell surface can not simply explain the phenomena, such as the level of virus growth, killing mechanisms of lymphocytes and host range of the virus. It is quite interesting to analyse which gene of the virus determines the characteristics of the virus.