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Summary. The reactivity of four different monoclonal antibodies (MAbs) with populations of Bacteroides fragilis NCTC 9343, enriched by density gradient centrifugation for a large capsule, small capsule and electron-dense layer (EDL) only visible by electronmicroscopy, was examined. The MAbs reacted strongly with polysaccharides present in both the large capsule-and EDL-enriched populations but not in the small capsule-enriched populations. The pattern of labelling was determined by immunoblotting, immunofluorescence and immuno-electronmicroscopy, and flow cytometry. The MAbs labelled cell membraneassociated epitopes in the large capsule-and EDL-enriched populations and cell-free material in the EDL population. By immunoblotting, ladders of repeating polysaccharide subunits were evident in the EDL population but not in the large capsule population. The proportion of cells labelled within each population was determined by flow cytometry. The reactivity of another MAb with the small capsule population was confirmed by flow cytometry. A qualitative indication of epitope expression was obtained by examination of the flow cytometric profiles. Differential expression of the same saccharide epitope was observed both between and within structurally distinct B. fragilis populations. The MAbs were speciesspecific and cross-reacted with several recent clinical isolates. These polysaccharides may be relevant to the virulence of B. fragilis.

The molecular biology of Mapuera virus was studied at both the protein and nucleic acid levels. Seven virusencoded proteins were detected in infected Vero cells. The sizes and characteristics of each of the proteins determined from various radiolabelling experiments allowed preliminary identification of the proteins as the large (L; 190 kDa), haemagglutinin neuraminidase (HN; 74 kDa), nucleocapsid (N; 66 kDa), fusion (Fo; 63 kDa), phosphoprotein (P; 49 kDa), matrix (M; 43 kDa) and non-structural (V; 35kDa) proteins. Western blot analysis showed that the HN, N and P proteins were major antigens recognized in the mouse. A cDNA library of total virus-infected cellular mRNA was created and screening of the library resulted in the detection of cDNA sequences representing the N mRNA transcript of Mapuera virus. The N mRNA sequence determined from the clones was 1731 nt in length and contained an ORF that encoded 537 amino acids, the complete 3' untranslated region and part of the 5' non-coding region. The calculated M r of the N protein was 59 kDa, which is close to the 66 kDa protein observed by SDS-PAGE.

SUMMARYSeveral strains of measles virus which did not agglutinate monkey erythrocytes in phosphate-buffered saline did so in buffer containing o.8 M-ammonium sulphate. Haemadsorption to cells infected with these viruses was also salt-dependent. In a series of tests salt-dependent agglutinin was shown to be a stable structural component of the infectious virion.The relevance of these findings is discussed in the light of previous reports that many measles virus preparations do not agglutinate erythrocytes.

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