Isotypes and IgG subclasses of anti-Fab antibodies in human immunodeficiency virus-infected hemophilia patients

We reported recently that anti-Fab autoantibodies of the IgG isotype are associated with the decrease of helper/inducer (CD4+) lymphocytes in human immunodeficiency virus-infected (HIV+) hemophilia patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC). In the present study we investigated the subclass distribution of IgG-anti-Fab autoantibodies, and whether anti-Fab antibodies of the IgA and IgM isotypes also are associated with the development of AIDS. Sera of HIV+ patients with AIDS had significantly higher IgA-anti-Fab activity than HIV+ patients with ARC (p < 0.02), HIV+ patients without AIDS/ARC (p < 0.0001), HIV-negative (HIV-) patients (p < 0.001), or healthy controls (p < 0.0001). An inverse association was found between IgA-anti-Fab activity and CD4+ cell counts (r = -0.396, p < 10(-6)). In contrast, no association of CD4+ cell counts was observed with IgM-anti-Fab. However, IgM-anti-Fab was significantly increased in patients with thrombocytopenia. We found a significant association between IgA-anti-Fab activity and serum neopterin concentrations (r = 0.310, p < 10(-5)). IgG-anti-Fab activity was detected mainly in the IgG3 fraction, although in HIV+ patients with AIDS/ARC various IgG subclasses were present. Affinity-purified anti-Fab antibodies isolated from sera of AIDS patients bound to rgp120-preincubated CD4+ cells of a healthy individual, supporting our hypothesis that anti-Fab antibodies and free circulating gp120 molecules are involved in the elimination of uninfected CD4+ cells. Removal of anti-Fab autoantibodies from the circulation by immune adsorbance might be a useful approach in the treatment of AIDS.

Complementarities and network interactions in AIDS

The contribution of autoimmune phenomena to the development of AIDS is not fully understood. In this paper we provide new evidence that idiotypic network interactions are operative in the development of AIDS. We furthermore present a model that involves two groups of antibodies and other molecules that are related to each other by a network of specific complementarities. We define Group I molecules to include antibodies and other molecules that have direct or indirect similarities with class I MHC molecules, and Group II substances that have similarities with class II MHC. We observe an inverse relationship between Group I antibodies (including anti-Fab) and Group II antibodies (including anti-anti-gp120, anti-anti-CD8 and anti-rCD4). The potential roles of members of these two groups in AIDS pathogenesis and/or protection are discussed.

Association of T cell and macrophage dysfunction with surface gp 120-immunoglobulin-complement complexes in HIV-infected patients

The mechanism of CD4+ cell depletion and functional T helper cell inhibition in HIV-infected individuals is poorly understood. The present study demonstrates that immune complex-covered CD4+ cells are associated with T cell inhibition and macrophage stimulation. We studied 30 patients with ARC/AIDS and 35 asymptomatic HIV+ haemophilia patients. Overall, 20 +/- 3% of peripheral CD4+ lymphocytes were covered with gp120 (range 0-94%). gp120+ cells also exhibited surface-bound IgG (P = 0.0001), IgM (P = 0.0001), and complement (P = 0.0001). Decreased in vitro lymphocyte proliferation was associated with the immune complex load of CD4+ cells. The higher the percentage of CD4+ gp 120+ cells in the blood, the lower the T cell response in vitro (P = 0.001). Moreover, an association was found between immune complex-positive cells and plasma neopterin (P = 0.01). Patients with increased plasma neopterin levels had decreased in vitro responses to pokeweed mitogen (PWM) (P = 0.006), phytohaemagglutinin (PHA) (P = 0.004), concanavalin A (Con A) (P = 0.09), and anti-CD3 MoAb (P = 0.03), and decreased CD4+ cell counts in the blood (P = 0.006). Since maximally 1% of CD4+ lymphocytes are infected with HIV, T cell dysfunction and T cell depletion in HIV-infected patients may also be caused by the release of free gp120 that binds to uninfected CD4+ cells. Our data suggest that the functional inhibition and subsequent elimination of uninfected CD4+ lymphocytes with surface gp120-immunoglobulin-complement complexes may be a pathomechanism in the manifestation of AIDS.

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

There is increasing evidence that autoimmune phenomena play an important role in the immunopathogenesis of AIDS. We found a high degree of sequence homology between HIV-1 and antigen receptor molecules, immunoglobulins and T cell receptors. Based on recent findings that the appearance of anti-Fab autoantibodies and attachment of gp120/immunoglobulin/complement complexes on CD4+ T cells are associated with the decrease of CD4+ T cells in HIV-infected patients, we hypothesize herein that cross-reactive anti-F (ab')2 autoantibodies and circulating gp120 molecules are responsible for a destabilization of the immune network and the elimination of CD4+ T cells.

IgA-anti-Fab autoantibodies and disease progression in AIDS

There is increasing evidence that autoimmune phenomena contribute to the pathogenesis of the acquired immunodeficiency syndrome (AIDS). We investigated the relationship between IgA autoantibodies directed against the Fab part of the IgG molecule and disease progression in 87 HIV-infected hemophilia patients. AIDS patients demonstrated a significantly higher serum IgA-anti-Fab activity than HIV-positive (HIV+) patients with AIDS-related complex (ARC) (P < 0.02), HIV+ patients without AIDS/ARC (P < 0.0001), HIV negative (HIV-) patients (P = 0.0001), or healthy controls (P < 0.0001). Moreover, an inverse association was observed between serum IgA-anti-Fab activity and CD4+ cell counts (r = -0.396, P < 10(-6)). This close association was confirmed in longitudinal studies of symptomatic patients. IgA-anti-Fab antibodies are suggested to play an important role in the immunopathogenesis of AIDS, and their determination may be helpful in the monitoring of HIV-infected patients.

CD4+ lymphocyte depletion in HIV-infected patients is associated with gp120-immunoglobulin-complement attachment to CD4+ cells

The mechanism of CD4+ lymphocyte depletion, which is the main immunological feature in HIV-infected patients, is unclear. We investigated whether gp120-immunoglobulin-complement complexes on the surface of CD4+ cells might be involved in the elimination of CD4+ lymphocytes. The results obtained in 63 HIV-infected patients show that gp120 is attached to a variable degree to CD4+ cells. Importantly, the percentage of CD4+gp120+ lymphocytes is inversely associated with CD4+ lymphocyte counts in the peripheral blood (p = 0.0004). CD4+gp120+ blood lymphocytes bind IgM (p = 0.0027) and IgG antibodies (p = 0.0001) and complement (p = 0.0005). These results suggest that immune complex-mediated cell elimination is an important mechanism of CD4+ cell depletion in patients with AIDS.

The association of kidney graft outcome with pretransplant serum IgG-anti-F(ab')2 gamma activity

Pretransplant sera of 474 kidney graft recipients were tested for IgG-anti-F(ab')2 gamma activity. The patients had significantly higher IgG-anti-F(ab')2 gamma activity than healthy controls (P = 0.0004). Serum lymphocytotoxic antibodies were correlated with IgG-anti-F(ab')2 gamma (P = 0.004), whereas CMV infection and blood transfusions were not. We found a significant association between pretransplant IgG-anti-F(ab')2 gamma activity and early and 1-year kidney graft outcome. This association was pronounced in recipients with no lymphocytotoxic antibodies. Recipients with immediately functioning grafts and a creatinine < 130 mumol/L at 1 year had strikingly higher pretransplant IgG-anti-F(ab')2 gamma activity than patients with graft failure (P < 0.0001).

Restriction mechanisms of B cell regulation by a physiological IgG-anti-immunoglobulin autoantibody

Immunization of LEW rats with strongly histoincompatible BN blood cells induces, in addition to anti-donor antibody, a broadly reactive IgG autoantibody which binds to IgG and IgM molecules (IgG anti-Ig). Minute amounts of affinity purified IgG anti-Ig (0.2 pg/10(6) cells) suppress the antibody production in vitro of antigen receptor (AgR)-stimulated B cells derived from rats of the same strain. The suppressive antibody is also active in the whole serum IgG fraction. Importantly, anti-Ig-induced suppression is governed by restriction mechanisms: only AgR-occupied B cells are affected, the suppression is cell cycle dependent, and maximum suppression is obtained at an optimum IgG concentration. Treatment of rats in vivo with 0.8 mg Ig-anti-Ig (whole IgG fraction) along with allogeneic cells resulted in nearly complete suppression of the anti-donor antibody response. Possible mechanisms of B cell suppression by IgG anti-Ig are crosslinking of AgR with FcR, or cocapping of the two receptors with sterical interaction as a consequence of their separate occupation. Both alternatives lead to the release of an inactivating signal.

Regulation of antibody response by an IgG-anti-Ig autoantibody occurring during alloimmunization. II. Selective inactivation of antigen receptor-occupied B cells

Heterologous antiimmunoglobulin antibodies are efficient regulators of the B cell response. We have shown that during the immune response against allogeneic cells the immune system develops autologous IgG-antiimmunoglobulin. A few molecules of this "physiological" autoantibody suppress the IgM production of one B cell in vitro. In the current series of experiments we further define the regulation of antigen receptor-activated B cells by this autoantibody. To mimic the in vivo situation, where IgG-anti-Ig appears a few days after alloimmunization, the antibody's effect on an already ongoing B cell response was studied. Interestingly, we found that the IgG-anti-Ig loses its suppressive effect when added to the cell culture 1 or 2 days after B cell activation, but that suppression can be completely restored when the cells are restimulated via their antigen receptor. Thus, the IgG-anti-Ig antibody suppresses B cells only when their antigen receptor is occupied. Even restimulated B cells become refractory 8 hr after activation, and later (24 hr) regain their susceptibility to IgG-anti-Ig-induced suppression. The Fc receptor is involved in mediating suppression since the antibody's suppressive capacity is abolished after removal of its Fc region. Possible mechanisms of B cell suppression by IgG-anti-Ig are crosslinking of antigen receptor with Fc receptor, or cocapping and functional interaction of the two receptors as a result of their separate occupancy. Our experiments demonstrate that B cell regulation by IgG-anti-Ig produced during an immune response to allogeneic cells is governed by 3 restriction mechanisms: antigen receptor occupancy, activation stage dependency, and optimal antibody concentration.

Anti-IgG autoantibodies in HIV-infected hemophilia patients

Sera of 76 HIV-negative hemophilia patients, 103 HIV-positive (HIV+) hemophilia patients free of AIDS or AIDS related complex (ARC), and 32 HIV+ hemophilia patients with AIDS/ARC were tested for four different anti-IgG activities. IgG-anti-F(ab')2 gamma, IgM-anti-F(ab')2 gamma, and IgG-anti-Fc gamma serum activities were significantly associated with the clinical stage of HIV infection, whereas IgM-anti-Fc gamma was not. IgG-anti-F(ab')2 gamma activity was found to be caused by cross-reaction of anti-HIV antibody with an epitope within the constant CH1 domain of human IgG. HIV+ hemophilia patients with severe thrombocytopenia (less than 50,000/microliters platelet counts) had significantly higher IgM-anti-IgG activity than patients with greater than 50,000/microliters platelets. Because anti-IgG antibodies possess immunoregulatory properties, our results may serve as a possible explanation for the frequent B cell disorders encountered in HIV-infected patients.

Striking inverse association of IgG-anti-Fab gamma antibodies and CD4 cell counts in patients with acquired immunodeficiency syndrome (AIDS)/AIDS-related complex

The contribution of autoimmune phenomena to the pathogenesis of acquired immunodeficiency syndrome (AIDS) is poorly understood. We investigated the relationship between IgG-anti-Fab gamma autoantibodies and the main immunologic feature of AIDS, the decrease of CD4+ helper lymphocytes. Sera of 33 human immunodeficiency virus (HIV) infected (HIV+) hemophilia patients with AIDS/AIDS-related complex (ARC), 57 HIV+ patients without AIDS/ARC, 23 HIV-negative (HIV-) patients, and 76 healthy controls were tested for antibody activity against the Fab region of IgG. Patients with AIDS/ARC had significantly higher IgG-anti-Fab gamma activity than HIV+ patients without AIDS/ARC, HIV- patients, or controls (P less than .0001). A striking inverse association was found between IgG-anti-Fab gamma and CD4+ cell counts (r = -.69; P less than 10(-6)). Sequential testing in 16 AIDS/ARC patients showed that an increase in the IgG-anti-Fab gamma activity was invariably accompanied by a decrease in the CD4+ cell count. IgG-anti-Fab gamma antibodies may play an important role in the immunopathogenesis of AIDS.

An immunoglobulin-specific autoantibody occurring during alloimmunization suppresses the antibody response

Our previous studies showed that a broadly reactive immunoglobulin G (IgG) anti-immunoglobulin (IgG-anti-Ig) autoantibody is induced during the immune response of LEW rats to BN blood cells. The present experiments analyze the immunoregulatory effect of this physiological autoantibody on antigen receptor-activated B cells in cell cultures. The results show that: (a) At 0.9 pg IgG-anti-Ig/10(6) B cells, an almost complete suppression of the antibody response is induced: we calculated that a few IgG-anti-Ig molecules are sufficient to suppress the antibody response of one B cell; (b) IgG-anti-Ig-induced B-cell suppression is dose-dependent; (c) IgG-anti-Ig suppresses B cells contained in their natural environment (mixed spleen cell population). These data demonstrate that the IgG-anti-Ig autoantibody is an extremely efficient regulatory molecule of the alloimmune response.

Pretransplant serum IgG-anti-F(ab')2gamma activity and kidney graft outcome: comparison of results obtained at two centers

Anti-IgG autoantibodies are reported to possess immunoregulatory properties. In the present study, we investigated the effect of pretransplant serum IgG-anti-F(ab')2gamma autoantibody activity on kidney graft outcome in recipients from two transplant centers.

An experimental model for preventing alloimmunization against platelet transfusions by pretreatment with antibody-coated cells

The pretreatment of LEW (RT-1l) rat recipients with antibody-coated BN (RT-1n) blood cells resulted in the suppression of the LEW antibody response against subsequent BN platelet and leukocyte transfusions. Both coating with homologous LEW-anti-BN serum or heterologous rabbit-anti-rat lymphocyte serum was effective. Repeated boosting with uncoated platelets or leukocytes did not abrogate the suppression. The degree of suppression was dependent on the amount of antibody used for cell coating. The induced suppression was also extended to uncoated antigens and unrelated third-party cells. The serum-IgG fraction of pretreated rats was strongly immunosuppressive, suggesting that the mechanism of suppression was related to the induction of a broadly reactive regulatory IgG.

Long-lasting kidney graft survival after immunization with antibody-coated blood cells: mediation by immunosuppressive autoantibodies

Treatment of LEW rats before transplantation with BN blood cells preincubated with LEW-anti-BN serum resulted in prolonged BN kidney graft survival (untreated, 8 +/- 0.4 days; pretreated, 124 +/- 36). The serum of pretreated animals contains a factor which suppresses T cell proliferation against donor antigens. This effect was not mediated by antiidiotypic antibodies because it was reproduced in a donor-unrelated system. The serum and IgG of pretreated animals also suppressed the humoral immune response. As for T cells, the antibody-suppressive effect was not donor-restricted. A broadly reactive anti-immunoglobulin (anti-B cell) autoantibody was found in the IgG fraction of immunized animals. The mediation of immunosuppression by broadly reactive anti-B and T cell autoantibodies induced by the immunization with antibody-coated blood cells is discussed.

Role of anti-IgG autoantibodies in kidney transplantation

To demonstrate whether anti-IgG autoantibodies of different isotypes and specificities play a role in kidney transplantation, pretransplant sera of recipients (a) with well-functioning grafts (n = 40); (b) with reversible rejection episodes that were treated successfully (n = 63); and (c) with irreversible graft rejection (n = 40) were tested for four different anti-IgG autoantibody activities. A protective effect of IgG-anti-F(ab)2 gamma antibodies on graft survival was observed (p less than 0.01). High pretransplant IgG-anti-Fc gamma activity was found to be associated with a low kidney graft survival rate (p less than 0.02). Pretransplant IgM-anti-F(ab)2 gamma and IgM-anti-Fc gamma activities showed no effect on kidney graft outcome.

Induction of a suppressive serum factor, prevention of sensitization, and prolongation of kidney graft survival in rats by transfusion with antibody-coated blood cells

Transfusion with antibody-coated allogeneic blood cells suppresses the cytotoxic antidonor antibody response in a strongly incompatible rat combination (BN----LEW). Cell coating with homologous recipient antidonor antiserum, rat monoclonal antibodies against MHC class I donor antigens, or rabbit antirat lymphocyte serum all were effective. The suppression was not abrogated by repeated booster transfusions with untreated donor blood. Moreover, the suppression extended to antibody-uncoated antigens present on the same donor cell. Not only the antibody response but also the Graft-versus-host reaction against donor antigens was suppressed. The serum of pretreated animals contained suppressive activity. It suppressed the cytotoxic antibody response as well as the cellular immune response (GVH) when transferred into syngeneic recipients. A weaker suppression of antibody response was obtained by transferring spleen cells of pretreated animals into syngeneic recipients. The transfer data suggest that broadly reactive serum factor(s) were mainly responsible for the suppressive effect. Transfusion with LEW-anti-BN-coated donor cells before transplantation induced markedly prolonged kidney graft survival in the BN----LEW combination without additional immunosuppression (untreated controls: 8.4 +/- 0.4, pretreated recipients: 124 +/- 36 days, P less than 10(-4)).