The structure of the extracellular polysaccharide from Rhizobium meliloti, a microsymbiont in the nitrogen fixing symbiosis, has been investigated. The polysaccharide contains a terminal @-D-glucopyranosyl group with pyruvic acid ketalically linked to its 4 and 6 positions. After removal of this substituent from the methylated polysaccharide the four sugar residues in the side chain were removed sequentially by specific degradations; each of these steps involved oxidation, p-elimination by treatment with base, and, when necessary, acid hydrolysis under mild conditions. The result of each degradation was followed by trideuteriomethylation, hydrolysis, and analysis of the product by GLC/MS. The sequence of the sugar residues in the main chain was determined using a modified Smith degradation in which the polyalcohol, obtained after periodate oxidation-borohydride reduction, was methylated before the mild acid hydrolysis. As a result of these studies, it is concluded that the polysaccharide is composed of octasaccharide repeating units with the structure 25.Biosynthetic and structural studies have revealed that many bacterial polysaccharides are composed of oligosaccharide repeating units* and the largest of these which have been conclusively demonstrated are hexasaccharide repeating units (cf. ref 2-4). There is strong justification for this occurrence of small repeating units since larger ones would require more complex systems of enzymes for their biosynthesis. Despite this, however, preliminary studies on the extracellular polysaccharide from Rhizobium meliloti have indicated that it should either be composed of octasaccharide repeating units or have a less regular s t r~c t u r e .~,~ We now report the structural elucidation of this polysaccharide, using specific degradations.

A complementarity-determining region (CDR) of the mouse monoclonal antibody (mAb) F58 was constrcted with specificity to a neutalization-indudng region of human immunodeficiency virus type 1 (1HV-1). The mAb has its major reactivity to the amino acid sequence I-GPGRA in the V3 viral envelope region. All CDRs including several framework amno acids were synthesized from the sequence deduced by cloning and sequencing mAb F58 heavy-and light-chain variable d . Peptides derived from the third heavy-chain domain (CDR-H3) alone or in combination with the olher CDR sequences competed with F58 mAb for the V3 region. The CDR-H3 peptide was chemicaly modified by cyclization and then inhibited HIV-1 replication as well as syncytium formation by infected cels. Both the homologous lllB viral strain to which the F58 mAb was induced and the heterologous SF2 strain were inhibited. This synthetic peptide had unexpectedly potent antiviral activity and may be a potential tool for treatment of IRV-infected persons.

The ESEN (European Sero-Epidemiology Network) project was established to harmonize the seroepidemiology of five vaccine preventable infections including measles, mumps and rubella in eight European countries. This involved achieving comparability both in the assay results from testing in different centres and also sampling methodology. Standardization of enzyme immunoassay results was achieved through the development of common panels of sera by designated reference centres. The panels were tested at the reference laboratory and then distributed to each participating laboratory for testing using their routine methods. Standardization equations were calculated by regressing the quantitative results against those of the reference laboratory. Our study found large differences in unitage between participants, despite all using an EIA method standardized against an international or local standard. Moreover, our methodology adjusted for this difference. These standardization equations will be used to convert the results of main serosurvey testing into the reference country unitage to ensure inter-country comparability.

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The complete amino acid (aa) sequence of the hepatitis B virus (HBV) core protein (HBcAg), ayw subtype, was synthesized as decapeptides with five overlapping aas. The peptides were tested for reactivity with monoclonal antibodies (mAbs) to HBcAg (35/312, 37/275, and 7/275). All the mAbs specifically inhibited human anti-HBc by cross competition in assays for anti-HBc and anti-HBe. The mAb 35/312 recognised a peptide covering residues 76-85 of the HBcAg sequence. The other two mAbs did not react specifically with any linear peptide, suggesting discontinuous epitopes for these mAbs. The linear sequence EDPASR at residues 77-82 was found to constitute the epitope for mAb 35/312 when fine mapping the binding site. The most essential aas for mAb 35/312 were found to be the DP at residues 79-80, when peptides were synthesized where the aas at 77-83, were substituted by the other 19 aas. Since the mAb 35/312 inhibits the binding of human anti-HBc positive sera, which are known to recognise an SDS labile epitope, the sequence 77-82 might be a part of a larger discontinuous epitope. Alternatively the mAb 35/312 blocks the binding of human anti-HBc by steric hindrance.

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Eighteen colorectal carcinoma patients without macroscopic disease after surgery were immunized using recombinant (r) human (h) carcinoembryonic antigen (CEA) with (n=9) or without (n=9) the addition of soluble granulocyte/macrophage-colony-stimulating factor (GM-CSF). The dose of rhCEA per immunization was 100 microg (n=6), 316 microg (n=6) or 1000 microg (n=6). rhCEA was given s.c. on day 1 and 80 microg/day of GM-CSF s.c. on days 1-4. The schedule was repeated six times during a period of 9 months. All patients in the GM-CSF group developed a strong rhCEA-dose-dependent IgG antibody response while only one-third of the non-GM-CSF patients mounted a weak antibody response. All patients (9/9) in the GM-CSF group developed a strong rhCEA-specific proliferative T cell response as well as type I T cells (interferon gamma secretion). In 45% of the patients also a weak type II T cell response (interleukin-4 secretion) was evoked. Both MHC-class-I- and -II restricted rhCEA-specific T cells were noted. A specific cellular response (proliferation and/or cytokine secretion) against native hCEA could be found in 8/9 patients in the GM-CSF group, although at a significantly lower level than against rhCEA. In the non-GM-CSF group a weak rhCEA-specific T cell response was induced. Three patients had a proliferative response, 4 patients type I T cells and 6 patients type II T cells. No signs of autoimmune reactions were noted. Local pharmacological administration of GM-CSF seemed to be a prerequisite for the induction of a strong immunity against baculovirus-produced hCEA protein. However, the cellular response against native CEA was of a significantly lower magnitude.