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We have investigated the use of a nested polymerase chain reaction assay for the detection of a fetal-specific Y-chromosomal sequence (DYS14) from DNA extracted from unsorted maternal peripheral blood. Serial dilutions of male DNA into female cord blood DNA indicated that the assay could detect an equivalent of a single male cell in 300,000 female cells. The assay exhibited absolute specificity for male DNA with no amplification from a DNA panel obtained from 10 female cord blood samples. When used on DNA extracted from unsorted peripheral blood from a series of pregnant women, the predictive values of a positive test for a male fetus were 86%, 67% and 87% in the first, second and third trimesters, respectively. We have also demonstrated that retesting the samples allows the detection of a proportion of male-bearing pregnancies with a high degree of accuracy, in that all 15 women who gave positive signals in two consecutive amplifications had male fetuses. We have also applied the test at 8 weeks postpartum to eight women who had previously delivered male babies; no Y-specific signal could be detected in any of them, suggesting that most women have cleared their circulation of fetal cells by 8 weeks after parturition.

Electron microscopic examination of a negatively stained suspension of Zinga virus showed particles 90-100 nm in diameter, enveloped with spikes 12-20 nm in length and 5 nm in diameter. Further identification of the virus by immune electron microscopy showed the reactivity of human Rift Valley fever virus-positive serum with Zinga virus. Results of this study are in agreement with earlier reports that Zinga virus is a strain of Rift Valley fever virus.

A carbon-based immunocytochemistry (CarBIC) method, whereby the epoxy resin is completely removed from a section prior to immunocytochemistry (IC), is described. The resulting absence of embedding medium allows for an optimal access of both primary antibodies and marker systems to structures at various levels throughout the depth of the section. A carbon film evaporated onto the surface of the section before extraction of the resin forms a base to which the section adheres and maintains structural integrity during subsequent processing. The conventional and accepted electron microscopical (EM) appearance for epoxy-resin-embedded material is regained by re-embedding in Epon before contrasting in the normal manner. The technique is demonstrated using human cytomegalovirus (HCMV)-infected human fibroblasts. HCMV+ serum is the source of primary antibodies and 10-nm protein A-gold (pA-G10) together with rabbit anti-human IgG + IgM is the marker for IC.

In the preceding study the degree of adsorption of virus to electron microscope grids has been shown to be an important parameter governing the efficiency of sedimentation techniques used for particle counting. In the present study the application of poly-L-lysine not only improves the binding ability but makes it more reproducible. In addition the distribution of adsorbed particles between grid bars and holes is characterized and its importance as an additional parameter for such techniques discussed. For accurate particle titre estimation and for assessing the efficiencies of sedimentation techniques in virus diagnostics the product of these parameters represents a correction factor which must be taken into consideration. Furthermore it could be demonstrated, using the technique here described over the surface of a poly-L-lysine treated grid after drying. This phenomenon makes possible the estimation of a titre through particle counting on gravimetrically determined volumes.

A test for the presence of antibodies in sera is described in which the binding of the antibody to a morphologically identifiable antigen, visualized using staphylococcal protein A-coated gold, serves as the criterion for specificity. This 'Antigen Controlled Immuno Diagnosis' (ACID test) as applied to T4 bacteriophage, vaccinia virus and Enterobacterium Yersinia has proved to be reliable and simple to carry out.