Improvement of rotavirus isolation in the cell culture by immune peroxidase staining

Processing of tissue culture cells

Live cells are often studied, in vitro, bathed in nutrient growth media. It is sometimes necessary to study individual compounds produced by these cells and antibodies work well for this purpose. These cells must first be concentrated and fixed before testing. There are a couple of ways to study cells in culture using antibodies. One is to fix the cells in place as they adhere to a solid surface and then test them as though they were cells on a slide. Another is to retrieve them and pellet the cells, fixing them in a test tube and then embedding and sectioning them as though they were a solid tissue. Fixatives can be mild to moderate depending on the antigens to be studied. Sectioned cells can be tested following mild pretreatment steps. Cells fixed in the culture dish can be tested following mild pretreatment steps in buffers containing 0.25% Triton X-100 and 5% dimethylsulfoxide (DMSO) to allow for easier antibody penetration. The endogenous peroxidase enzyme or oxidative compounds can be quenched in a mild hydrogen peroxide solution. The sections are then ready to test with antibody after an incubation in a normal serum solution blocks any available charged sites.

Improvement of the specificity of enzyme immunoassays for the detection of rotavirus and adenovirus in fecal specimens

A variable rate of false-positive results may be observed with commercial enzyme immunoassays (EIAs) for the detection of rotavirus and adenovirus antigen in stool specimens, depending on the quality of the reagents and the presence of potentially interfering substances in stool samples. The present study was performed in an attempt to improve the specificity of current commercial rotavirus and adenovirus EIAs without significant loss of sensitivity by optimizing the cut-off value. A collective of 174 stool samples obtained from children suffering from acute gastroenteritis was tested. Electron microscopy (EM) and PAGE were used as reference methods for rotavirus detection. For the evaluation of the adenovirus kits, virus isolation in cell culture and the polymerase chain reaction served as reference standards. The highest sensitivity for rotavirus and adenovirus detection was achieved by the Ridascreen(R) Rotavirus and Ridascreen Adenovirus. However, the Ridascreen(R) Rotavirus and Ridascreen Adenovirus produced the highest number of false-positive results (n = 9) for each rotavirus and adenovirus detection. Cross-reactivities to coronaviruses and reoviruses were observed with the rotavirus antigen EIAs. For Rotazyme II, Ridascreen Rotavirus and Ridascreen Adenovirus, the specificity could be markedly increased without loss of sensitivity by doubling the cut-off value. For the alternative immunoassays, which were overall more specific, it was not possible to significantly decrease the rate of false-positive results without impairment of sensitivity by raising the cut-off value. In conclusion, at least for some rotavirus and adenovirus antigen EIAs, the cut-off value set by the manufacturer may not permit an optimal differentiation between true-positive and -negative samples. By raising the cut-off value from 50 to 100%, the specificity of two rotavirus antigen and one adenovirus antigen EIA can be improved markedly without significant loss of sensitivity.

Congenital rubella syndrome after maternal reinfection

This report concerns a case of congenital rubella syndrome (CRS) with atypical immune response affecting an infant whose mother had repeated evidence of immunity before pregnancy. Laboratory diagnosis of CRS could only clearly be achieved by virus isolation after the second month of life despite typical clinical features of CRS and multiple organ involvement. After the first month of age, low concentrations of specific IgM antibodies were revealed by ELISA and confirmed by a reference test system (IgM-specific haemagglutination inhibition assay). Persistent and increasing high levels of IgM antibodies were detected only after the 6th month of life. Later on IgG antibody levels decreased. Immunological investigations showed an IgG1-hypoglobulinaemia. The unusual feature of the present case report is not only the failure of the maternal rubella immunity to prevent CRS, but the defect of the child's immune system, probably attributable to congenital infection. As a consequence, laboratory diagnosis of CRS could not be achieved initially by the proved serological methods.