Regulation of IgG production by suppressor Fc gamma RII+ T hybridomas

Fc receptors as targets for immunotherapy

Human membrane and soluble Fc epsilon receptors (Fc epsilon RI, Fc epsilon RII/CD23) and Fc gamma receptors (Fc gamma RI/CD64, Fc gamma RII/CD32, Fc gamma RIII/CD16) have been implicated in a number of diseases. Their functional roles such as capture and clearance of immune complexes, antibody-dependent cell cytotoxicity, or cytokine or inflammatory mediator release, make them potential targets for immuno-intervention. In the present review, we will describe how membrane and soluble human Fc epsilon R and Fc gamma R have been already used as targets/tools for immuno-interventions by using monoclonal and bispecific engineered antibodies. Some therapeutic uses of these molecules both in cancer, infectious, and auto-immune diseases are presented.

Immune complexes from immunized mice and infected cystic fibrosis patients mediate murine and human T cell killing of hybridomas producing protective, opsonic antibody to Pseudomonas aeruginosa

We examined the basis for the absence in cystic fibrosis (CF) patients of opsonic antibodies to the mucoid exopolysaccharide (MEP) antigen surrounding Pseudomonas aeruginosa that infect these patients. Opsonic antibodies to MEP are found in sera of the minority of CF patients that remain noncolonized into the second to fourth decades of life and protect rodents from chronic P. aeruginosa endobronchial infections. High titers of nonopsonic antibodies to MEP are found in P. aeruginosa-infected CF patients. Immunization of mice with doses of MEP that provoke only nonopsonic antibodies elicited CD3+, CD8+, T cell receptor alpha beta receptor+, major histocompatibility complex-unrestricted cytotoxic lymphocytes specific for hybridoma cells producing opsonic but not nonopsonic antibodies. Cytotoxicity was dependent on immune complexes on the surface of the T cells. Normal murine T cells could be activated by concanavalin A and sensitized with immune complexes for cytotoxic killing of hybridoma targets. CF patients infected with P. aeruginosa had serum immune complexes that sensitized concanavalin A-activated human T cells to kill murine hybridoma cells producing opsonic but not nonopsonic antibody. These results could explain the absence in infected CF patients of MEP-specific opsonins, an occurrence that accompanies the persistence of this infectious state.

In vitro inhibition of tumor B cell growth by IgG-BF-producing Fc gamma RII+ T cell hybridoma and by immunoglobulin G-binding factors

The growth-modulating effect on mouse hybridoma B cells of IgG-BF-producing Fc gamma RII+ mouse T cell hybridomas and of the IgG-BF isolated from the culture supernatants of these cells has been examined. Cocultures of IgG-secreting hybridoma B cells with IgG-BF-producing T hybridomas or with partially purified IgG-BF demonstrated a reproducible inhibition of the tumor B cell growth. The inhibition was due to a cytostatic and not to a cytotoxic effect. Hybridoma B cells cultured in liquid medium in the presence of soluble IgG-BF, or cocultured in semisolid agarose assays with IgG-BF-producing hybridoma T cells did not undergo immediate cytolysis but were prevented from proliferating. Thus, our data indicate that IgG-BF-producing Fc gamma RII+ T cells interfere with the proliferation of transformed B cells, possibly through soluble IgG-BF.

Increased levels of soluble low-affinity Fc gamma receptors (IgG-binding factors) in the sera of tumour-bearing mice

Soluble forms of low affinity Fc gamma receptors (Fc gamma R), also called IgG-binding factors (IgG-BF), have been shown to play a regulatory role in immune responses. By using an immunodot assay with the anti-mouse Fc gamma R MoAb, 2.4G2, the levels of IgG-BF have been measured in the sera of mice bearing syngeneic tumours of lymphoid or non-lymphoid origin or in mice injected with high doses of murine IgG. These sera contained large amounts of IgG-BF as compared with controls. In the case of mice bearing IgG2a- or IgG2b-secreting hybridomas or lymphomas, serum IgG-BF increased progressively with tumour size and serum monoclonal IgG concentration, reaching 4-12 times the normal levels. A less than three-fold increase was found in mice bearing an IgG1-secreting hybridoma or tumours which do not secrete IgG (IgA-secreting hybridoma, non-immunoglobulin-secreting lymphoid tumours or melanoma) or in mice injected with 9 mg of monoclonal IgG2a. The enhancement of serum IgG-BF levels was independent of the expression of Fc gamma R by the tumour cells, suggesting that the majority of IgG-BF secreted in response to tumours was produced by the host rather than by the tumour. The increased production of IgG-BF may participate in the control of tumour growth and in the modulation of the host immune responses in tumour-bearing animals.

Regulation of antibody production mediated by Fc gamma receptors, IgG binding factors, and IgG Fc-binding autoantibodies

Fc receptors (FcRs) are immunoglobulin-binding structures that enable antibodies to perform a variety of functions by forming connections between specific recognition and effector cells. Besides eliciting cytotoxicity, inducing secretion of mediators and endocytosis of opsonized particles, FcRs are involved in the regulation of antibody production, both as integral membrane proteins and as soluble molecules released from the cell surface. Most FcRs belong to the same family of proteins as their ligands (immunoglobulin superfamily). This review contains recent data obtained by use of monoclonal antibodies and cloning studies on FcRs and FcR-like molecules. The importance of fine specificity of receptor binding site(s)--that of the conformation of FcRs and their ligands in triggering signaling mechanisms--is analyzed. The regulatory function of membrane-bound and -released FcRs; the correlation between cell cycle, FcR expression, and release; as well as the possible mechanisms of these phenomena are discussed.

Structural differences among guinea pig Fc gamma 1/gamma 2 receptors on macrophages, polymorphonuclear cells, and lymphocytes

Using the cDNA, D-3, coding for Fc gamma 1/gamma 2 receptor of guinea pig macrophages that binds IgG1 and IgG2 (Fc gamma 1/gamma 2R), we examined the cell distribution of this receptor by RNA blot analysis. The Fc gamma 1/gamma 2R mRNA was expressed in polymorphonuclear cells and B cells as well as in macrophages, but not at the detectable level in T cells. The cDNA amplified from RNA of polymorphonuclear cells in the polymerase chain reaction was the same as D-3. The cDNA of B cells was found to have about 140 bp cDNA segment inserted to the cytoplasmic tail of D-3. We found that the cDNA amplified from T cell RNA differed in signal peptide and extracellular domain sequence from cDNAs of other cell types. This cDNA does not seem to be amplified from the mRNAs of contaminating other cell types.