Detection of virus-specific polymeric immunoglobulin A in acute hepatitis A, C, E virus serum samples using novel chimeric secretory component.

OBJECTIVE: To conduct a proof-of-concept study on preferential binding of polymeric IgA (pIgA) using a novel recombinant rabbit/human chimeric secretory component (cSC) and preliminary assessment of the diagnostic potential of virus-specific pIgA in discriminating acute hepatitis A, E, and C (HAV, HEV, HCV) patients and uninfected controls using an indirect enzyme-linked immunoassay. RESULTS: cSC binds > 0.06 µg/ml of purified human and mouse pIgA with negligible cross-reactivity against IgM and IgA. Virus-specific pIgA was significantly higher in serum of acute HAV (n = 6) and HEV (n = 12) patients than uninfected samples (HEV: p < 0.001; HAV: p = 0.001), and had low correlation with virus-specific IgM (HEV r: - 0.25, 95% CI - 0.88 to 0.71, p = 0.636; HAV r: 0.05, 95% CI - 0.54 to 0.60, p: 0.885). Anti-HCV pIgA peaked early in HCV seroconversion panels (n = 14), and was undetectable after 4 weeks post-primary bleed, even in ongoing infections, while serum anti-HCV IgA, IgG and IgM persisted. Patients with early acute HCV infection had significantly higher levels of anti-HCV pIgA compared to those with chronic infections (p < 0.01). The use of novel cSC demonstrates the presence of virus-specific pIgA in sera of patients with acute HAV, HEV, and HCV infection, and posits its potential utility as a diagnostic biomarker that warrants further validation on larger sample populations.

Site-selective solid-phase synthesis of a CCR5 sulfopeptide library to interrogate HIV binding and entry.

Tyrosine (Tyr) sulfation is a common post-translational modification that is implicated in a variety of important biological processes, including the fusion and entry of human immunodeficiency virus type-1 (HIV-1). A number of sulfated Tyr (sTyr) residues on the N-terminus of the CCR5 chemokine receptor are involved in a crucial binding interaction with the gp120 HIV-1 envelope glycoprotein. Despite the established importance of these sTyr residues, the exact structural and functional role of this post-translational modification in HIV-1 infection is not fully understood. Detailed biological studies are hindered in part by the difficulty in accessing homogeneous sulfopeptides and sulfoproteins through biological expression and established synthetic techniques. Herein we describe an efficient approach to the synthesis of sulfopeptides bearing discrete sulfation patterns through the divergent, site-selective incorporation of sTyr residues on solid support. By employing three orthogonally protected Tyr building blocks and a solid-phase sulfation protocol, we demonstrate the synthesis of a library of target N-terminal CCR5(2-22) sulfoforms bearing discrete and differential sulfation at Tyr10, Tyr14, and Tyr15, from a single resin-bound intermediate. We demonstrate the importance of distinct sites of Tyr sulfation in binding gp120 through a competitive binding assay between the synthetic CCR5 sulfopeptides and an anti-gp120 monoclonal antibody. These studies revealed a critical role of sulfation at Tyr14 for binding and a possible additional role for sulfation at Tyr10. N-terminal CCR5 variants bearing a sTyr residue at position 14 were also found to complement viral entry into cells expressing an N-terminally truncated CCR5 receptor.

Alteration of the Fc gamma RIIa dimer interface affects receptor signaling but not ligand binding.

The aggregation of cell surface FcRs by immune complexes induces a number of important Ab-dependent effector functions. However, despite numerous studies that examine receptor function, very little is known about the molecular organization of these receptors within the cell. In this study, protein complementation, mutagenesis, and ligand binding analyses demonstrate that human FcgammaRIIa is present as a noncovalent dimer form. Protein complementation studies found that FcgammaRIIa molecules are closely associated. Mutagenesis of the dimer interface, as identified by crystallographic analyses, did not affect ligand binding yet caused significant alteration to the magnitude and kinetics of receptor phosphorylation. The data suggest that the ligand binding and the dimer interface are distinct regions within the receptor, and noncovalent dimerization of FcgammaRIIa may be an essential feature of the FcgammaRIIa signaling cascade.

Unique monoclonal antibodies define expression of Fc gamma RI on macrophages and mast cell lines and demonstrate heterogeneity among subcutaneous and other dendritic cells.

The mouse Fc gamma RI is one of the most fundamentally important FcRs. It participates in different stages of immunity, being a low affinity receptor for T-independent IgG3 and yet a high affinity receptor for IgG2a, the product of a Th1 immune response. However, analysis of this receptor has been difficult due largely to the failure to generate specific Abs to this FcR. We have made use of the polymorphic differences between BALB/c and NOD/Lt mice to generate mAb specific for the Fc gamma RI of BALB/c and the majority of in-bred mouse strains. Three different mAb were obtained that detected Fc gamma RI encoded by the more common Fcgr1(a) and Fcgr1(b) alleles, and although they identified different epitopes, none inhibited the binding of IgG to Fc gamma RI. When bound to Fc gamma RI, these mAb induced calcium mobilization upon cross-linking. Several novel observations were made of the cellular distribution of Fc gamma RI. Resting and IFN-gamma-induced macrophages expressed Fc gamma RI as well as mast cell lines. Both bone marrow-derived and freshly isolated dendritic cells from spleen and lymph nodes expressed Fc gamma RI. A class of DC, uniquely found in s.c. lymph nodes, expressed the highest level of Fc gamma RI and also high levels of MHC class II, DEC205, CD40, and CD86, with a low level of CD8 alpha, corresponding to the phenotype for Langerhans-derived DC, which are highly active in Ag processing. Thus, in addition to any role in effector functions, Fc gamma RI on APC may act as a link between innate and adaptive immunities by binding and mediating the uptake of T-independent immune complexes for presentation, thereby assisting in the development of T-dependent immune responses.

FcgammaRI-deficient mice show multiple alterations to inflammatory and immune responses.

The inactivation of the mouse high-affinity IgG Fc receptor FcgammaRI resulted in a wide range of defects in antibody Fc-dependent functions. These studies showed the primary importance of FcgammaRI in endocytosis of monomeric IgG, kinetics, and extent of phagocytosis of immune complexes, in macrophage-based ADCC, and in immune complex-dependent antigen presentation to primed T cells. In the absence of FcgammaRI, antibody responses were elevated, implying the removal of a control point by the deletion of FcgammaRI. In addition, FcR-gamma chain-deficient mice were found to express partially functional FcgammaRI. Thus, FcgammaRI is an early participant in Fc-dependent cell activation and in the development of immune responses.