Elizabeth Fischer

Natural autoantibodies and complement promote the uptake of a self antigen, human thyroglobulin, by B cells and the proliferation of thyroglobulin-reactive CD4(+) T cells in healthy individuals.

Serum from normal individuals contains substantial amounts of natural antibodies (NA) capable of recognizing self antigens. However, the physiological implications of this autoreactivity remain unclear. We have examined the role of self‐reactive NA and complement in mediating the uptake of human thyroglobulin (Tg) by human peripheral B cells in reconstituted whole blood. Significant binding of fluorescein isothiocyanate‐conjugated‐Tg to B cells was observed, and absorption of Tg‐reactive antibodies from serum markedly reduced this uptake, as did inactivation of serum complement or blockade of complement receptor types 1 (CR1, CD35) and 2 (CR2, CD21). T cell responsiveness to Tg was examined in a preparation of peripheral blood mononuclear cells (PBMC) cultured in the presenceof autologous serum. A subset of CD4+ T cells exhibited a dose‐dependent proliferative response to Tg, which was strongly inhibited by complement inactivation and by immunoabsorption of Tg‐reactive antibodies. Furthermore, this T cell response was abrogated by depletion of B cells from the PBMC culture. These data imply that uptake of complement‐opsonized Tgu2009/u2009anti‐Tg complexes andsubsequent presentation of Tg by B cells are prerequisites for the proliferation of Tg‐reactive CD4+ T cells, suggesting a novel role for natural autoantibodies and complement in the regulation of autoreactivity under physiological conditions.

Functional properties of soluble CD21.

Soluble receptors may display immunoregulatory properties by blocking interactions between ligands and their membrane receptors or by triggering specific biologic responses through interaction with counter part membrane receptors. A natural soluble form of CD21 that is cleaved from lymphocyte membrane CD21 circulates in normal human serum. Soluble CD21 retains the capacity to bind iC3b and CD23, the known ligands of membrane CD21. In a similar fashion to IgE complexes, another ligand of CD23, the soluble CD21 was shown to efficiently trigger CD23-signalling pathways in human monocytes. By inducing release of proinflammatory cytokines and upregulating expression of molecules involved in antigen presentation, soluble CD21 modulates critical monocyte functions that may be relevant to allergic and inflammatory disorders.

Sulfonated dextran inhibits complement activation and complement-dependent cytotoxicity in an in vitro model of hyperacute xenograft rejection

In the present study, we demonstrate that a substituted soluble dextran derivative bearing 73% carboxylic groups and 15% benzylamide sulfonate groups, termed CMDBS25, inhibits complement activation and complement-mediated damage in an in vitro model of xenogeneic rejection. Incubation of porcine aortic endothelial cells with normal human serum resulted in time-dependent complement consumption as assessed by C3a generation in the fluid phase and deposition of activated complement fragments C3, C5 and of C5b-9 on target cells. The presence of C5b-9 membrane attack complex was associated with 51Cr release from prelabelled endothelial cells. The addition of 5-25 mg of CMDBS25/ml under the experimental conditions used, inhibited complement activation and C3a generation in a dose-dependent fashion. CMDBS25 (25 mg/ml) totally suppressed iC3b, C5 and C5b-9 cytolytic complex deposition on cells and inhibits by 42% lysis of target endothelial cells. Native dextran had no effect. Our observations document the anti-complementary properties of sulfonated dextran derivatives and their potential as therapeutic agents for the prevention of complement-dependent hyperacute xenograft rejection.

Ligation of CR1 (C3b receptor, CD35) on CD4+ T lymphocytes enhances viral replication in HIV-infected cells

The present study provides evidence for a role of the C3b receptor, CR1 (CD35), in activation of HIV replication in CD4+ T lymphocytes. Ligation of CR1 with cross‐linked anti‐receptor MoAbs or with aggregated C3b enhanced transcription of viral genes and the release of p24 and RT activity from cultures of purified normal CD4+ T lymphocytes that had been infected with HIV‐1 in vitro. No effect was observed upon ligation of CR2 (CD21), a C3 receptor that is also expressed on human CD4+ T cells. Cross‐linking of CR1 also enhanced HIV replication in peripheral blood CD4+ lymphocytes isolated from HIV+ individuals. The enhancing effect of CR1 was not related to a mitogenic effect induced by stimulation of the receptor on T cells. The CR1 specificity of the enhancing effect was established by the observation that the addition of soluble recombinant CR1 to the cultures abolished the enhancement of p24 release induced by anti‐CR1 MoAbs. Our results suggest that HIV replication may be triggered in resting HIV‐infected CD4+ T lymphocytes through interaction with C3b‐bearing immune complexes or particles.

The human immunodeficiency virus preventive vaccine research at the French National Agency for acquired immunodeficiency syndrome research

The human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic is of unprecedented gravity and is spreading rapidly, notably in the most disadvantaged regions of the world. The search for a preventive vaccine is thus an absolute priority. For over 10 years the French National Agency for AIDS research (ANRS) has been committed to an original program combining basic science and clinical research. The HIV preventive vaccine research program run by the ANRS covers upstream research for the definition of immunogens, animal models, and clinical research to evaluate candidate vaccines. Most researchers in 2004 believe that it should be possible to obtain partial vaccine protection through the induction of a strong and multiepitopic cellular response. Since 1992, the ANRS has set up 15 phases I and II clinical trials in order to evaluate the safety and the capacity of the candidate vaccines for inducing cellular immune responses. The tested candidate vaccines were increasingly complex recombinant canarypox viruses (Alvac) containing sequences coding for certain viral proteins, utilized alone or combined with other immunogens (whole or truncated envelope proteins). ANRS has also been developing an original strategy based on the utilization of lipopeptides. These comprise synthetic fragments of viral proteins associated with lipids that facilitate the induction of a cellular immune response. These approaches promptly allowed the assessment of a prime-boost strategy combining a viral vector and lipopeptides.

Evidence for the role of CRT (CD35), in addition to CR2 (CD21), in facilitating infection of human T cells with opsonized HIV

Complement activation by HIV results in the binding of C3 fragments to the gp160 complex and enhanced infection of C3 receptor-bearing target cells. We have studied complement-mediated enhancement of infection of the human CD4-positive T-cell line HPB-ALL which expresses the CR1 (CD35) and CR2 (CD21) receptors for C3. CR1 and CR2 are present on 15% and 40% of normal peripheral blood CD4-positive T lymphocytes respectively. Opsonization of the virus with complement resulted in a 3- to 10-fold enhancement of infection of HPB-ALL cells, as assessed by measuring the release of p24 antigen in culture supernatants throughout the culture period. Blockade of CR2 with cross-linked anti-CR2 monoclonal antibodies decreased infection to the level observed with unopsonized virus. Blocking CR1 reduced complement-mediated infection by 50-80%. Experiments using serum deficient in complement factor I demonstrated that CR1 mediates the interaction between opsonized virus and T cells in addition to its ability to serve as a cofactor for the cleavage of C3b into smaller fragments that interact with CR2. A requirement for CD4 in complement-mediated enhancement of infection was observed with HIV-1 Bru but not with HIV-1 RF. Thus, CR1 and CR2 contribute in an independent and complementary fashion to penetration of opsonized virus into complement receptor-expressing T cells. Involvement of CD4 in infection with opsonized virus depends on the viral strain.