The complement system in HIV disease

Distinction of early complement classical and lectin pathway activation via quantification of C1s/C1-INH and MASP-1/C1-INH complexes using novel ELISAs

The most commonly used markers to assess complement activation are split products that are produced through activation of all three pathways and are located downstream of C3. In contrast, C4d derives from the cleavage of C4 and indicates either classical (CP) or lectin pathway (LP) activation. Although C4d is perfectly able to distinguish between CP/LP and alternative pathway (AP) activation, no well-established markers are available to differentiate between early CP and LP activation. Active enzymes of both pathways (C1s/C1r for the CP, MASP-1/MASP-2 for the LP) are regulated by C1 esterase inhibitor (C1-INH) through the formation of covalent complexes. Aim of this study was to develop validated immunoassays detecting C1s/C1-INH and MASP-1/C1-INH complex levels. Measurement of the complexes reveals information about the involvement of the respective pathways in complement-mediated diseases. Two sandwich ELISAs detecting C1s/C1-INH and MASP-1/C1-INH complex were developed and tested thoroughly, and it was investigated whether C1s/C1-INH and MASP-1/C1-INH complexes could serve as markers for either early CP or LP activation. In addition, a reference range for these complexes in healthy adults was defined, and the assays were clinically validated utilizing samples of 414 COVID-19 patients and 96 healthy controls. The immunoassays can reliably measure C1s/C1-INH and MASP-1/C1-INH complex concentrations in EDTA plasma from healthy and diseased individuals. Both complex levels are increased in serum when activated with zymosan, making them suitable markers for early classical and early lectin pathway activation. Furthermore, measurements of C1-INH complexes in 96 healthy adults showed normally distributed C1s/C1-INH complex levels with a physiological concentration of 1846 ± 1060 ng/mL (mean ± 2SD) and right-skewed distribution of MASP-1/C1-INH complex levels with a median concentration of 36.9 (13.18 - 87.89) ng/mL (2.5-97.5 percentile range), while levels of both complexes were increased in COVID-19 patients (p<0.0001). The newly developed assays measure C1-INH complex levels in an accurate way. C1s/C1-INH and MASP-1/C1-INH complexes are suitable markers to assess early classical and lectin pathway activation. An initial reference range was set and first studies showed that these markers have added value for investigating and unraveling complement activation in human disease.

Plasma Levels of Complement Factor I and C4b Peptides Are Associated with HIV Suppression

Individuals who exhibit long-term HIV suppression and CD4 T-cell preservation without antiretroviral therapy are of great interest for HIV research. There is currently no robust method for rapid identification of these “HIV controller” subjects; however, HLA-B*57 (human leukocyte antigen (major histocompatibility complex), class I, B*57) genotype exhibits modest sensitivity for this phenotype. Complement C3b and C4b can influence HIV infection and replication, but studies have not examined their possible link to HIV controller status. We analyzed HLA-B*57 genotype and complement levels in HIV-positive patients receiving suppressive antiretroviral therapy, untreated HIV controllers, and HIV-negative subjects to identify factors associated with HIV controller status. Our results revealed that the plasma levels of three C4b-derived peptides and complement factor I outperformed all other assayed biomarkers for HIV controller identification, although we could not analyze the predictive value of biomarker combinations with the current sample size. We believe this rapid screening approach may prove useful for improved identification of HIV controllers.

Neuroinflammation and Behavior in HIV-1 Transgenic Rats Exposed to Chronic Adolescent Stress

Highly active antiretroviral therapy (HAART) has improved prognosis for people living with HIV (PLWH) and dramatically reduced the incidence of AIDS. However, even when viral load is controlled, PLWH develop psychiatric and neurological disorders more frequently than those living without HIV. Adolescents with HIV are particularly susceptible to the development of psychiatric illnesses and neurocognitive impairments. While both psychiatric and neurocognitive disorders have been found to be exacerbated by stress, the extent to which chronic stress and HIV-1 viral proteins interact to impact behavior and relevant neuroinflammatory processes is unknown. Determination of the individual contributions of stress and HIV to neuropsychiatric disorders is heavily confounded in humans. In order to isolate the influence of HIV-1 proteins and chronic stress on behavior and neuroinflammation, we employed the HIV-1 transgenic (Tg) rat model, which expresses HIV-1 proteins with a gag and pol deletion, allowing for viral protein expression without viral replication. This Tg line has been characterized as a model of HAART-controlled HIV-1 infection due to the lack of viral replication but continued presence of HIV-1 proteins. We exposed male and female adolescent HIV-1 Tg rats to a mixed-modality chronic stress paradigm consisting of isolation, social defeat and restraint, and assessed behavior, cerebral vascularization, and neuroinflammatory endpoints. Stress, sex, and presence of the HIV-1 transgene impacted weight gain in adolescent rats. Female HIV-1 Tg rats showed decreases in central tendency during the light cycle in the open field regardless of stress exposure. Both male and female HIV-1 Tg rats exhibited decreased investigative behavior in the novel object recognition task, but no memory impairments. Adolescent stress had no effect on the tested behaviors. Microglia in female HIV-1 Tg rats exhibited a hyper-ramified structure, and gene expression of complement factor B was increased in the hippocampus. In addition, adolescent stress exposure increased microglial branching and junctions in female wild-type rats without causing any additional increase in HIV-1 rats. These data suggest that the presence of HIV-1 proteins during development leads to alterations in behavioral and neuroinflammatory endpoints that are not further impacted by concurrent chronic adolescent stress.

Complement receptor 2 is expressed in neural progenitor cells and regulates adult hippocampal neurogenesis

Injury and inflammation are potent regulators of adult neurogenesis. As the complement system forms a key immune pathway that may also exert critical functions in neural development and neurodegeneration, we asked whether complement receptors regulate neurogenesis. We discovered that complement receptor 2 (CR2), classically known as a coreceptor of the B-lymphocyte antigen receptor, is expressed in adult neural progenitor cells (NPCs) of the dentate gyrus. Two of its ligands, C3d and interferon-α (IFN-α), inhibited proliferation of wild-type NPCs but not NPCs derived from mice lacking Cr2 (Cr2(-/-)), indicating functional Cr2 expression. Young and old Cr2(-/-) mice exhibited prominent increases in basal neurogenesis compared with wild-type littermates, whereas intracerebral injection of C3d resulted in fewer proliferating neuroblasts in wild-type than in Cr2(-/-) mice. We conclude that Cr2 regulates hippocampal neurogenesis and propose that increased C3d and IFN-α production associated with brain injury or viral infections may inhibit neurogenesis.

Immunological analysis in paediatric HIV patients at different stages of the disease

There are only few clinical studies on complement in well-defined (or characterized) paediatric HIV patients. Aim of this study was to evaluate the complement system and immunoglobulins in HIV-infected children and to correlate data to stage of disease. Blood samples of 127 HIV-infected children (11-134 months; 62 male : 65 female) were collected in order to evaluate humoral immunity. The patients were classified according to CDC clinical (N-asymptomatic; A-mild symptoms such as common recurrent infections; B-moderate symptoms such as Candidiasis and herpes infections, meningitis, sepsis and anaemia; C-severe symptoms such as opportunistic infections and neoplasia) and with respect to immunological criteria (T CD4(+) cell count). Analysis of complement system included the classical (CH50), alternative (APH50) pathway activities and plasma concentrations of mannan-binding lectin (MBL), of the C4 allotypic variants C4A and C4B. (ELISA), and of the C3 split product C3d (rocket immunoeletrophoresis). Immunodiagnosis also included CD4(+) and CD8(+) lymphocyte count and immunoglobulin concentrations. Complement activation and consumption was observed in all patients correlating with disease activity. Activated classical and alternative pathways and elevated C3d were significantly correlated with immunologic category 3. C3d levels were also significantly correlated with immunologic category 1. Undetectable CH50 and APH50 were found in two (group C) and 10 patients (n = 2, A = 2, B = 2, C = 4), respectively. Low MBL values were found in 13/127 but without correlation to disease severity. Undetectable C4B levels were observed in three patients, favouring the diagnosis of a complete deficiency. Although not related to clinical symptomatology, a strong ongoing complement activation can be observed in all stages of HIV infection. In contrast to earlier reports MBL could not be considered as a risk factor for HIV.

Presence of the variant mannose-binding lectin alleles associated with slower progression to AIDS. Amsterdam Cohort Study

OBJECTIVE

To examine the association between mannose-binding lectin (MBL) polymorphism and progression to AIDS and death in HIV-1 infection.

DESIGN AND METHODS

In 131 HIV-1-infected homosexual seroconverters, survival analyses were performed to determine both the association between MBL genotype and time from HIV-1 seroconversion to AIDS and death, and time from AIDS to death.

RESULTS

Of the 131 seroconverters, of whom 61 developed AIDS, 76 were typed as homozygous wild-type and 55 as carriers of variant alleles (52 heterozygous and three homozygous variant alleles). A Survival analyses suggested that HIV-1-infected men with the variant alleles progressed somewhat slower to AIDS [relative hazard (RH), 0.62; 95% confidence interval (CI), 0.36-1.10] and death (RH, 0.73; 95% CI, 0.42-1.25). Interestingly, CD4+ T-cell count determined at the moment of AIDS was found to be significantly lower among persons with the mutation (97 x 10(6)/l versus 204 x 10(6)/l; P=0.03). Furthermore, when AIDS-free times before the diagnosis of an opportunistic infection were compared with those preceding a diagnosis of Kaposi's sarcoma, Kaposi's sarcoma diagnosis was more postponed than that of an opportunistic infection (RH, 0.21; 95% CI, 0.05-0.95; versus RH, 0.67; 95% CI, 0.35-1.27).

CONCLUSION

Indications for a weak pre-AIDS protective effect of variant MBL alleles were demonstrated.

Influence of host genes on HIV-1 disease progression

The role of host genes in the course of HIV-1 infection has been examined in different populations and among all major risk groups. Two extended human lymphocyte antigen (HLA) haplotypes, HLA A1-Cw7-B8-DR3-DQ2 and HLA A11-Cw4-B35-DR1-DQ1, are found to be associated with a faster progression to AIDS. The complement C4 factor and tumor necrosis factor genes of the major histocompatibility complex, as well as the mannose binding protein gene, have also been suggested to influence the outcome of AIDS. The recent discovery that chemokine receptors could serve as cofactors for HIV-1 cell entry has prompted a search for polymorphisms in chemokine receptor genes. A 32 base pair inactivating deletion in the CCR5 gene and a point mutation within the CCR2b gene resulting in a conservative amino acid substitution have been examined and shown to be independently associated with delayed disease progression. Together, these observations strongly support a genetic component in AIDS pathogenesis. This article synthesizes the current state of knowledge about the influence of host genes on HIV-1 disease progression. It provides a summary of all significant association studies reported so far. The role of the allelic polymorphism in these genes is discussed with regard to the immunopathogenesis of AIDS.

Role of Complement and Antibodies in the Control and Facilitation of HIV Disease

In humans the HIV infection results in a chronic disease with a permanent fight between factors controlling HIV and the escape of the virus. Fromthese control mechanisms the present review summarizes the role betwen complement and autoantibodies; the competition of complement and anti-HIV antibodies for binding sites, the role of mannan-binding lectin in the susceptibility to and in the survival after HIV infection, the contribution of complement-dependent enhancing type antibodies to the clinical progression of HIV disease as well as the changing pattern of some autoantibodies (mimicking MHC class II molecules, anti-heat shock protein 60 antibodies and anti-C1q antibodies) which were found to correlate to immunological and clinical parameters.

Genetic predisposition to HIV-1 infection and acquired immune deficiency virus syndrome: a review of the literature examining associations with HLA [corrected]

Researchers have been studying the relationship between host HLA type and the immune response to HIV-1 since early in the AIDS epidemic. Although the literature is replete with suggestions of an association, the exact locus and nature is unclear. This article reviews the current HLA-HIV/AIDS literature, providing a complete summary of all significant associations reported in journal articles (N = 30) between 1982 and 1993. Consistent associations with alleles comprising the haplotype DQ2-DR3-B8-Cw7-A1 and AIDS progression support a genetic component in AIDS progression. DQ1-DR1-B35-Cw4-A11 and DR5 also show consistent associations with HIV/AIDS outcomes, although it is unclear whether they are measuring susceptibility to HIV-1 infection, AIDS progression, or both. The question of whether HLA influences susceptibility to HIV-1 infection remains unanswered, as well-designed studies addressing this topic are lacking. Similarly, further studies are needed to clarify if HLA type is associated with KS. Several issues that complicate across-study comparisons are discussed including heterogeneity of both HLA and AIDS, potential confounding by race or risk group, and other biases which may influence results. In addition, several proposed biologic mechanisms are explored.

HIV and human complement: mechanisms of interaction and biological implication

Human complement, although not lytic for HIV-1, interacts with the virus and is closely involved in the infectious process. It enhances infection in the absence of antibody, and turns neutralizing antibodies into agents which increase viral infectivity. In this review M.P. Dierich et al. summarize available information and discuss possible biological implications.

HIV in Hungary

HIV infection in Hungary has not reached the frightening proportions that are currently ravaging other parts of the world. Given this relatively fortunate position and the now clear understanding of the ways in which HIV is transmitted, vigorous public education programmes have been undertaken to minimize the spread of the virus. Here, George Füst outlines these efforts, discusses diagnosis and monitoring of infected patients, and describes HIV research in Hungary.

Complement research: biosynthesis, genetics, immunoregulatory role and clinical studies

Complementology is one of the major areas of immunological research in Hungary. Here, András Falus and colleagues describe studies on the control of biosynthesis of complement components and on the nature and function of receptors in the complement system.