Immunofluorescence for detection of antibodies against human cytomegalovirus-induced membrane antigens

Stereoscopic Imaging of Single Molecules at Plasma Membrane of Single Cell Using Photoreduction-Assisted Electrochemistry

Stereoscopic imaging of single molecules at the plasma membrane of single cell requires spatial resolutions in 3 dimensions (x-y-z) at 10-nm level, which is rarely achieved using most optical super-resolution microscopies. Here, electrochemical stereoscopic microscopy with a detection limit down to a single molecule is achieved using a photoreduction-assisted cycle inside a 20-nm gel electrolyte nanoball at the tip of a nanopipette. On the basis of the electrochemical oxidation of Ru(bpy)3 2+ into Ru(bpy)3 3+ followed by the reduction of Ru(bpy)3 3+ into Ru(bpy)3 2+ by photogenerated isopropanol radicals, a charge of 1.5 fC is obtained from the cycling electron transfers involving one Ru(bpy)3 2+/3+ molecule. By using the nanopipette to scan the cellular membrane modified with Ru(bpy)3 2+-tagged antibody, the morphology of the cell membrane and the distribution of carcinoembryonic antigen (CEA) on the membrane are electrochemically visualized with a spatial resolution of 14 nm. The resultant stereoscopic image reveals more CEA on membrane protrusions, providing direct evidence to support easy access of membrane CEA to intravenous antibodies. The breakthrough in single-molecule electrochemistry at the cellular level leads to the establishment of high-resolution 3-dimensional single-cell electrochemical microscopy, offering an alternative strategy to remedy the imperfection of stereoscopic visualization in optical microscopes.

Binding of human and animal immunoglobulins to the IgG Fc receptor induced by human cytomegalovirus

Human cytomegalovirus (HCMV)-infected cells express a virus-encoded receptor that is able to bind the Fc part of IGG: Some basic binding properties of this Fc receptor (FcR) have been examined. The affinity constant (K(a)) for human IgG Fc fragment in its interaction with acetone-fixed, HCMV-infected human embryonic lung fibroblasts was estimated to be around 2 x 10(8) M(-1) and the number of binding sites was estimated to be around 2 x 10(6) per cell. Of the human IgG, IgA, IgM and IgD classes, only IgG reacted with the receptor, and all four of the IgG subclasses were reactive. IgG from rabbit, hamster, cat, swine and horse exhibited binding to the HCMV FcR, in contrast to IgG from mouse, rat, guinea pig, dog, sheep, goat, cow and chicken. Immunoglobulins with and without HCMV IgG FcR-binding properties, like IgG from rabbit and mouse, can be of value in revealing the functional importance of the receptor. When the immunoglobulins were tested against herpes simplex virus type 1-induced FcR, both similarities and differences in immunoreactivity were seen relative to the HCMV FcR, which makes it unlikely that the binding sites for these two herpesvirus FcRs on the IgG molecule are identical.

Human antibody reactivity against the lower matrix protein (pp65) produced by cytomegalovirus

The lower matrix protein (pp65) is a major product of many laboratory strains of cytomegalovirus (CMV). It is thus an integral part of many CMV serological assays based on native antigen. Recombinant fragments of pp65 have previously been investigated for their usefulness in more-defined assays. The latter antigens have, however, failed to develop a positive response with serum samples derived from a substantial number of infected individuals. Here we show that the human humoral immune response to CMV pp65 is highly diverse and recognizes at least seven distinct but in some cases partly overlapping epitopes. Most of these epitopes could not be mimicked by any of the investigated recombinant or synthetic antigens. Furthermore, when we investigated the ability of human CMV-seropositive serum samples to block the reactivity of pp65-specific antibodies recognizing five different epitopes within pp65, it was evident that several sera did not contain significant levels of antibodies against any of these or overlapping structures. It was thus concluded that the antibody response against CMV pp65 is weak in some CMV-infected individuals, making this antigen unsuitable for use alone in serological screening systems for CMV infection.

Natural killing of fibroblasts infected with low-passage clinical isolates of human cytomegalovirus

Fibroblasts infected with most low-passage clinical isolates of human cytomegalovirus (CMV) were as susceptible to lysis by human natural killer (NK) cells as high passage AD-169-infected fibroblasts. NK lysis occurred despite the absence of detectable CMV-specific late membrane antigen(s) on the majority of the target cells infected with most of the low passage strains. The magnitude of NK lysis of different CMV-infected target cells did not correlate with their ability to induce IFN-alpha. NK cell-mediated lysis of cells infected with low-passage clinical isolates of CMV required both NK cells and HLA-DR+ accessory cells, as previously shown for AD-169-infected target cells.