Ultrastructural localization of viral antigens using the protein A-gold technique

The role of the major tegument protein VP8 of bovine herpesvirus-1 in infection and immunity

The tegument of bovine herpesvirus-1 (BHV-1) carries an abundant protein of 96 kDa, termed VP8. Immunolabeling using VP8-specific antiserum and colloidal gold-labeled protein A as the electron-dense marker was used to identify VP8 in the virions and virus-infected cells. VP8 was confirmed to be a tegument protein that, like the herpes simplex virus-1 homologue VP13/14, contains O-linked carbohydrates. VP8 was found in the nucleus of virus-infected cells as early as 2 hr postinfection. Since VP8 is a gamma2 protein, this protein cannot be newly synthesized at this time and must be acquired from the inoculum. This supports the hypothesis that early during infection, VP8 has a function in modulation of alpha gene expression. Later during infection, VP8 was observed in the cytoplasm around nucleocapsids and in dense inclusions, which accumulated in the cisternae of the Golgi. In addition, de novo-synthesized VP8 continued to accumulate in the nucleus in dense areas and around nucleocapsids. In calves, VP8 stimulated T cell proliferation and antibody production, both after BHV-1 challenge and after immunization with purified VP8. These results suggest a role for VP8 in the induction of humoral and specifically cell-mediated immunity to BHV-1.

Electron microscopy of mouse thymic virus

Thymuses of mice infected with mouse thymic virus (MTV), a herpesvirus, were examined with the electron microscope. Damage was manifested by distortions of cells, nuclei, and other organelles, with cellular aggregation apparent at advanced stages of necrosis. Infected cells also contained MTV particles and filaments. Negative staining showed that naked MTV capsids were icosahedral in shape with diameters ranging from 95 to 110 nm. Enveloped capsids appeared spherical and ranged in diameter from 125 to 165 nm. Immunogold labeling revealed the presence of antigenic sites around both naked and enveloped capsids, and also on the 10 nm filaments. The use of electron microscopy and immunohistochemical techniques as diagnostic tools to demonstrate MTV infection could prove valuable for the detection of the infection and the study of its pathogenesis.

Ultrastructure and protein A-gold immunolabelling of HRT-18 cells infected with turkey enteric coronavirus

The Minnesota strain of turkey enteric coronavirus (TCV) was propagated in HRT-18 cells, a cell line derived from human rectum adenocarcinoma. A productive non-cytopathic infection was established, without a previous adaptation, in these cells as shown by the specific hemagglutinating activity in cell culture supernatants. A post-embedding immunochemical technique, using specific antiserum directed against the original egg-adapted virus and colloidal-gold-labelled protein A as the electron-dense marker, was used for the identification of the virus and related antigens in the cells by electron microscopy. Budding of typical coronavirus particles, through intracytoplasmic membranes and accumulation of complete virus within cytoplasmic vesicles or the lumen of rough endoplasmic reticulum, were the main features of the viral morphogenesis. Late in infection, numerous progeny viral particles were shown at the outer surface of infected cells, but budding could not be demonstrated at this level. Two different types of surface projections were observed on the extracellular particles of this avian coronavirus. These morphological characteristics have been thus far described only for mammalian hemagglutinating coronaviruses.

Rapid titration of bovine, caprine and human RS virus by a micro-immunoperoxidase assay using a monoclonal antibody and a permissive ovine kidney cell line

An indirect immunoperoxidase micro-assay, using a continuous cell line derived from ovine kidney cells (OK) and a previously characterized monoclonal antibody (7C2), specific for an exposed and highly conserved epitope of the fusion protein of different strains of RS virus, was used advantageously to rapidly titrate bovine, caprine and human strains of RSV by either quantal (TCID50) or plaque forming assays. Virus titers, obtained in less than 36 h, were in agreement with those obtained by the conventional plaque assays which required an incubation period of 4 days or more. This assay is also applicable to micro-neutralization of fusion inhibition assays for testing serum or screening monoclonal antibodies.

Electron microscopic method for determining the concentration of influenza virus antihemagglutinin antibodies of the IgG class

A novel technique for the determination of the concentration of influenza virus antihemagglutinin antibody of the IgG class is described which is based on the following principle: graded doses of purified antibody are allowed to react with homologous virus, resulting in binding of a portion of antibody. The virus-bound antibody is electron microscopically counted after labeling with protein A-gold. Since Freundlich's lambda-formula is valid for describing the relationship between antibody bound per virus particle and the corresponding concentration of unbound antibody, the values of bound antibody recorded can be used for calculating the concentration of unbound antibody. The antibody concentration of the test sample is obtained as sum of bound and unbound antibody. The antibody concentrations measured by use of this technique agreed well with chemically determined values.

Ultrastructural and immunogenic changes in the formation of mycetoma grains

The differences in the fine structure and antigenic determinants of mycetoma fungi in the mycelial phase in vitro and in grains in vivo facilitate an interpretation of grain formation. Aggregates of hyphal elements with multiple and thickened walls was a feature of the fungi in vivo. Associated with hyphal wall material, numerous polysaccharide microfibrils were detected in grains of Madurella mycetomatis. These were not seen associated with hyphal elements in vitro and it is suggested that these structures may be concerned with the aggregation of fungal elements in the formation of grains. Antibodies directed against the fungi in vitro were shown, by indirect immunogold labelling, to bind at identical sites in fungal material grown in vitro as in mycetoma grains. However the grain matrix was not labelled, suggesting that part of the structure formed in vivo is composed of modified antigen or is host derived.

Detection of HTLV-III/LAV antigens in peripheral blood lymphocytes from patients with AIDS

HTLV-III was searched for in frozen sections of peripheral blood lymphocytes obtained from AIDS patients by an immunofluorescence technique. Human IgG against HTLV-III/LAV and monoclonal antibodies against HTLV-III/LAV P 24 antigen, yielded a strong cytoplasmic fluorescence in frozen sections of the lymphocytes. Some cells containing HTLV-III antigens displayed multinucleated giant forms. They also reacted with monoclonal antibodies against helper/inducer T-cells (OKT4+), as demonstrated by direct double staining immunofluorescence. Similarly, complexes of immunoglobulins and C3 component of complement were also detected on HTLV-III/LAV Ag expressing lymphocytes. Immunofluorescence study of frozen sections of peripheral blood lymphocytes appeared to be a simple, fast and reliable method for detection of HTLV-III/LAV Ag in AIDS patients.

Ultrastructural demonstration of retrovirus antigens with immuno-gold staining in prodromal acquired immune deficiency syndrome

The peripheral lymphocytes of a patient with prodromal acquired immune deficiency syndrome contained giant multivesicular bodies. These were specifically stained by immuno-gold labelled polyclonal antibodies against the major core protein p24 of bovine leukaemia virus and human T cell leukaemia virus I. Moreover, the patient's serum was positive for bovine leukaemia virus by the ELISA method.

Immunoelectron microscopic localization of rabies virus antigen in central nervous system and peripheral tissue using low-temperature embedding and protein A-gold

A protein A-gold technique was used in conjunction with low temperature embedding to visualize ultrastructurally mature virions and sites of viral replication in the brains of rabies virus-infected mice after peripheral inoculation of virus. The association of viral profiles and gold particles with synaptic membranes, microtubules and rough endoplasmic reticulum suggested a mechanism of rabies virus transport within the central nervous system. Early interactions of inflammatory cells with the virus inoculum were characterized by phagocytosis by non-degranulating neutrophils and mononuclear cells.