Circulating immune complexes in HIV-infected persons

Antigen-specific antibody Fc glycosylation enhances humoral immunity via the recruitment of complement

HIV-specific broadly neutralizing antibodies (bNAbs) confer protection after passive immunization, but the immunological mechanisms that drive their development are poorly understood. Structural features of bNAbs indicate that they originate from extensive germinal center (GC) selection, which relies on persistent GC activity. However, why a fraction of infected individuals are able to successfully drive more effective affinity maturation is unclear. Delivery of antigens in the form of antibody-immune complexes (ICs), which bind to complement receptors (CRs) or Fc receptors (FcRs) on follicular dendritic cells, represents an effective mechanism for antigen delivery to the GC. We sought to define whether IC-FcR or CR interactions differ among individuals who develop bNAb responses to HIV. Enhanced Fc effector functions and FcR/CR interactions, via altered Fc glycosylation profiles, were observed among individuals with neutralizing antibody responses to HIV compared with those without neutralizing antibody activity. Moreover, both polyclonal neutralizer ICs and monoclonal IC mimics of neutralizer antibodies induced higher antibody titers, higher-avidity antibodies, and expanded GC B cell reactions after immunization of mice via accelerated antigen deposition within B cell follicles in a complement-dependent manner. Thus, these data point to a direct role for altered Fc profile/complement interactions in shaping the maturation of the humoral immune response, providing insights into how GC activity may be enhanced to drive affinity maturation in next-generation vaccine approaches.

Characteristics of Circulating Immune Complexes in HIV-Infected Patients with Different Viral Load

Serum concentration of antiviral antibodies was measured in HIV-infected patients with different viral load. It was found that higher concentrations of HIV-antigens correspond to higher titer of antiviral antibodies. Circulating immune complexes were isolated from patients' serum to estimate their size and immunoglobulin composition. High levels of small IgG- and IgM-containing complexes were identified in HIV-infected patients. In patients receiving antiretroviral treatment, the content of these complexes was significantly lower than in patients with high HIV load. This attests to positive role of specific therapy in preventing immune complex-associated pathology in HIV patients.

Slow turnover of HIV-1 receptors on quiescent CD4+ T cells causes prolonged surface retention of gp120 immune complexes in vivo

Peripheral blood CD4(+) T cells in HIV-1(+) patients are coated with Ig. However, the causes and consequences of the presence of Ig(+) CD4(+) T cells remain unknown. Previous studies have demonstrated the rapid turnover of viral receptors (VRs) on lymphoma and tumor cells. The present study investigates the turnover of VRs on peripheral quiescent CD4(+) T cells (qCD4s), which are the most abundant peripheral blood CD4(+) T cells. Utilizing pharmacological and immunological approaches, we found that the turnover of VRs on qCD4s is extremely slow. As a result, exposure to gp120 or HIV-1 virions in vitro causes gp120 to remain on the surface for a long period of time. It requires approximately three days for cell-bound gp120 on the surface to be reduced by 50%. In the presence of patient serum, gp120 forms surface immune complexes (ICs) that are also retained for a long time. Indeed, when examining the percentages of Ig(+) CD4(+) T cells at different stages of HIV-1 infection, approximately 70% of peripheral resting CD4(+) T cells (rCD4s) were coated with surface VRs bound to slow-turnover gp120-Ig. The levels of circulating ICs in patient serum were insufficient to form surface ICs on qCD4s, suggesting that surface ICs on qCD4s require much higher concentrations of HIV-1 exposure such as might be found in lymph nodes. In the presence of macrophages, Ig(+) CD4(+) T cells generated in vitro or directly isolated from HIV-1(+) patients were ultimately phagocytosed. Similarly, the frequencies and percentages of Ig(+) rCD4s were significantly increased in an HIV-1(+) patient after splenectomy, indicating that Ig(+) rCD4s might be removed from circulation and that non-neutralizing anti-envelope antibodies could play a detrimental role in HIV-1 pathogenesis. These findings provide novel insights for vaccine development and a rationale for using Ig(+) rCD4 levels as an independent clinical marker.

Molecular bases of immune complex pathology

The binding of antigens with antibodies forms immune complexes in the body. Usually these complexes are eliminated by the system of mononuclear phagocytes without development of pathological changes. This review highlights principal mechanisms responsible for safe removal of immune complexes in primates and humans. Special attention is given to diseases known as "immune complex diseases", when antigen-antibody complexes induce inflammatory reactions. The review considers key experimental works that significantly contributed to current knowledge of etiology and pathogenesis of type III hypersensitivity. Some factors of the development of immune complex syndrome such as level of humoral immune response to antigen, isotype and affinity of forming antibodies, the amount of immune complexes, and the consequences of their interaction with the complement system and Fc-receptors are analyzed based on the molecular mechanisms involved. The review contains a retrospective analysis of the most significant scientific achievements in immune complex pathology investigation within the last 100 years.

Gliadin IgG antibodies and circulating immune complexes

OBJECTIVE

Circulating immune complexes (CICs) in blood are associated with autoimmune-diseases such as systemic lupus erythematosus, immune complex glomerulonephritis, rheumatoid arthritis and vasculitis. However, slightly increased serum concentrations of such CICs are sometimes also found in healthy individuals. The objective of the current study was to assess whether food antigens could play a role in the formation of CICs.

MATERIAL AND METHODS

A total of 352 (265 F, 87 M), so far, healthy individuals were tested for CICs containing C1q and immunoglobulin G (IgG) as well as for gliadin IgG antibodies using the ELISA technique. Additionally, fructose and lactose malabsorption was assessed using hydrogen breath tests.

RESULTS

In our study, 15.3% (54/352) of the patients presented with elevated CIC concentrations (above 50 microg/ml) and 6.5% (23/352) of the study population were positive for gliadin IgG antibodies (above 20 U/ml). CIC concentration levels were significantly higher in the group with elevated gliadin IgG antibodies (CIC median: 49.0 microg/ml) compared with the group with normal levels of gliadin IgG antibodies (CIC median: 30.0 microg/ml; Mann-Whitney U-test, U=1992; p <0.001). As expected, there was no difference in CIC concentrations (Mann-Whitney U-test, U=6106; p=0.783) and gliadin IgG (Mann-Whitney U-test, U=3761; p=0.411) between patients in the fructose or lactose malabsorber groups and the subjects without malabsorption.

CONCLUSIONS

The results of this study indicate that certain food antigens (e.g. gluten) could play a role in the formation of CICs. An association between CICs and fructose or lactose malabsorption seems to be improbable.

Immunoglobulin and complement complexes in blood following infection with human immunodeficiency virus type 1

Freely soluble and complexed plasma immunoglobulin A (IgA), IgG, IgM, C1q, C3, and factor B in 36 human immunodeficiency virus type I (HIV-1)-seronegative controls, 69 asymptomatic HIV+ subjects, and 117 individuals with symptomatic HIV-associated disease were characterized. Levels of free and complexed IgG and IgA, and to a lesser extent free C1q and complexed IgM, increased with HIV-1 infection. In stark contrast, both HIV+ groups showed three- to sixfold declines in complexed C3, C1q, and factor B levels. The asymptomatic HIV+ population showed declines in levels of C3-bound IgA, IgG2, and IgG4 complexes. The asymptomatic group showed reductions in C3-complexed IgM, IgA, IgG2, and IgG4 levels. HIV infection is associated with complement-deficient immune complexes.

Phenotypic and functional changes in peripheral blood monocytes during progression of human immunodeficiency virus infection. Effects of soluble immune complexes, cytokines, subcellular particulates from apoptotic cells, and HIV-1-encoded proteins on monocytes phagocytic function, oxidative burst, transendothelial migration, and cell surface phenotype

We postulated that changes in the cell surface display of molecules that facilitate cell-cell and cell-matrix adhesions may reflect the changing immunosurveillance capacity of blood monocytes during progression of human immunodeficiency virus (HIV) infections. In Centers for Disease Control (CDC) stage A patients, whose monocytes' ability to phagocytose bacteria and generate reactive oxygen intermediates is often increased, the frequency of monocytes expressing CD49d, HLA-DP, HLA-DQ, and an activation epitope of CD11a/CD18 was increased and monocyte transendothelial migration was unimpaired. In CDC stage B/C patients, whose monocytes' ability to phagocytose bacteria and migrate across confluent endothelial monolayers was diminished, surface expression of CD49e and CD62L and the percentage of monocytes expressing CD18, CD11a, CD29, CD49e, CD54, CD58, CD31, and HLA-I were significantly decreased. Incubating normal donor monocytes with immune complexes in vitro reproduced the phenotypic and functional abnormalities seen in stage B/C patients. By contrast, in vitro stimulation with subcellular particulates released by apoptotic lymphocytes reproduced changes seen in stage A patients' monocytes. Although circulating monocytes appear to be activated at all stages, these data suggest that the high levels of circulating immune complexes, found predominantly in the later stages of HIV infection, may be particularly instrumental in reducing the monocyte's capacity to maintain surveillance against infection.

The Impact of Clotting Factor Concentrates on the Immune System in Individuals With Hemophilia

All reported studies to date, whether comparative or not, have shown a tendency toward a slower decrease in CD4+ numbers in patients receiving very high-purity agents with the rapidity in fall-off being affected by level of CD4+ numbers (low CD4+ numbers decreasing more rapidly), age (older persons showing more rapid CD4+ cell fall-off), and anti-HIV therapy. Clearly, these observations need to be extended in numbers, and the high-purity agents should also be similarly compared with the very high-purity therapies.