Evaluation of two serological methods for potency testing of whole cell pertussis vaccines.

The European Pharmacopoeia (Ph. Eur.) and the World Health Organization (WHO) require the performance of extensive quality control testing including a potency test before a vaccine batch is released for human use. Whole cell pertussis (wP) vaccine potency is assessed by a mouse protection test (MPT) based on the Kendrick test. This test compares the vaccine dose necessary to protect 50% of mice against the effect of a lethal intracerebral dose of Bordetella pertussis and the dose of a suitable reference vaccine needed to give the same protection level. Due to the large variability in the results of this test and the severe distress which is inflicted on the many animals involved, its replacement by an alternative method is highly desirable. At the initiative of the European Directorate for the Quality of Medicines and HealthCare (EDQM) of the Council of Europe, in collaboration with the WHO and the In-vitro toxicology Unit/European Centre for the Validation of Alternative Methods (ECVAM) of the European Commission (EC) Joint Research Centre-Institute for Health and Consumer Protection (JRC-IHCP), wP vaccine specialists from all over the world were invited to present an overview of candidate alternatives at a symposium organised in Geneva (Switzerland) in March 2005. Although no alternative method was found suitable for immediate implementation of batch potency control, the Pertussis Serological Potency Test (PSPT), initially developed in mice and recently transferred to guinea pigs (gps), was identified as a model of interest. Using the PSPT in gps to test several components of combined vaccines such as Diphtheria-Tetanus-wP vaccines in the same animal series would allow further implementation of the European 3Rs policy to batch potency control, by additional method refinement and reduction of animal use. The present study evaluated 2 features of the serological response to wP vaccination: 1) the overall antibody response as measured by a "whole cell" ELISA (PSPT-wC-ELISA) which uses the B. pertussis 18323 challenge strain prescribed for the MPT to coat the assay plates and 2) the functional neutralising antibodies to pertussis toxin (PT, one of the main virulence factors of B. pertussis), as measured by the Chinese Hamster Ovary (CHO) cell assay. The results showed that 1) the gp model can be used for wP vaccine potency testing; 2) despite good repeatability and precision, the CHO cell assay did not generate results comparable to the MPT. Moreover, the CHO cell assay showed significant differences in the ability of wP vaccines to induce neutralising anti-PT antibodies, which did not correlate to the overall antibody response evaluated by PSPT-wC-ELISA; 3) comparable potencies were obtained in the MPT and the PSPT-wC-ELISA. This study, supported by the previous ones correlating the PSPT-wC-ELISA in mice with the MPT, confirms that PSPT-wC-ELISA in gps is a promising approach for batch release potency testing of wP vaccines for which consistency in production has already been demonstrated by the MPT. However, a large scale validation study is required prior to the adoption of PSPT-wC-ELISA as a compendial reference method for wP vaccines batch release control.

Interleukin-1 gene polymorphisms and gastric cancer risk in a high-risk Italian population.

OBJECTIVES: Host genetic factors, including the IL1 gene cluster, play a key role in determining the long-term outcome of Helicobacter pylori infection. The aim of the study was to investigate the relationship between selected IL1 loci polymorphisms and gastric cancer risk in an Italian population. METHODS: In a case-control study we compared the IL1B-31 and IL1B+3954 biallelic and IL1RN pentaallelic variable number of tandem repeats (VNTR) polymorphisms in 185 gastric cancer patients and 546 controls randomly sampled from the general population of an area at high gastric cancer risk (Tuscany, Central Italy). RESULTS: Genotype frequencies of the IL1B-31 T/C, IL1B+3954 C/T, and IL1RN polymorphisms among our population controls were in Hardy-Weinberg equilibrium. In multivariate analyses, no increase in gastric cancer risk was observed for the IL1B-31*C- and IL1B+3954*T- carriers; a significant 50% increase emerged for IL1RN*2 allele carriers (OR = 1.49; 95% CI: 1.01-2.21). Analyses based on combined genotypes showed also that the association with IL1RN*2 allele was limited to two-variant allele carriers who were also homozygous for the IL1B-31*T allele (OR = 2.23; 95% CI: 1.18-4.23) with a statistically significant interaction between these two genotypes (p= 0.043). Haplotype analysis showed an increased risk for the haplotype IL1RN*2/IL1B-31*T. CONCLUSIONS: Our results suggest that host genetic factors (such as the IL1RN and the IL1B-31 polymorphisms) interact in the complex process of gastric carcinogenesis in this high-risk Italian population. Overall, this effect appears more modest than previously reported in other populations, supporting the hypothesis that other still-to-be-defined factors are important in gastric carcinogenesis. These findings might be due to a haplotype effect.

Demonstration of a peptidoglycan-linked lipoprotein and characterization of its trypsin fragment in the outer membrane of Brucella spp.

The sodium dodecyl sulfate (SDS) extraction-trypsin digestion protocol used by Braun and Sieglin (V. Braun and U. Sieglin, Eur. J. Biochem. 13:336-346, 1970) to show the peptidoglycan-linked lipoprotein of Escherichia coli was applied to both Brucella abortus and E. coli. Whereas a single polypeptide of 8,000 molecular weight was obtained from E. coli, several proteins of apparent molecular weight lower than 35,000 were demonstrated by SDS-polyacrylamide gel electrophoresis in B. abortus. These results did not change when the trypsin digestion conditions were modified. On the other hand, when the SDS extractions were performed under conditions more stringent than those used for other gram-negative bacteria, only a polypeptide fragment of apparent molecular weight of 8,000 was obtained from B. abortus. This polypeptide was similar to the trypsin fragment of the E. coli lipoprotein with respect to its behavior in SDS-polyacrylamide gels, isoelectric point in urea, molecular weight, and presence of both ester- and amide-linked fatty acids. Moreover, the amino acid analysis showed an overall similarity with respect to the amino acid composition of E. coli lipoprotein. A polypeptide of the same molecular weight, isoelectric point, and amino acid composition was also obtained from Brucella ovis by the same method. These results demonstrated that B. abortus and B. ovis cell envelopes contain a lipoprotein and strongly support the hypothesis that it is the only major protein covalently linked to the peptidoglycan.

Brucella outer membrane lipoprotein shares antigenic determinants with Escherichia coli Braun lipoprotein and is exposed on the cell surface.

In an enzyme-linked immunosorbent assay (ELISA), purified Brucella abortus and Escherichia coli peptidoglycan-linked lipoproteins gave a strong cross-reaction with sera from rabbits hyperimmunized with the heterologous lipoprotein. When smooth E. coli cells were used as ELISA antigens, the immunological cross-reaction was not observed unless the cells were treated to remove lipopolysaccharide and other outer membrane components. In contrast, intact cells from smooth strains of B. abortus and Brucella melitensis bound anti-lipoprotein immunoglobulin G, and the controls performed by ELISA showed that this reaction was not due to antibodies to the lipopolysaccharide, group 3 outer membrane proteins, or porins. Electron microscopy of cells labeled with antilipoprotein serum and protein A-colloidal gold showed specific labeling of smooth cells from both B. abortus and B. melitensis, even though unspecific labeling by nonimmune serum was observed with rough B. abortus. These results confirm the close similarity between E. coli and Brucella peptidoglycan-linked lipoproteins and show that, in contrast to E. coli, the lipoprotein of B. abortus and B. melitensis is partially exposed on the surface of smooth cells.

Serological response to the outer membrane lipoprotein in animal brucellosis.

The presence of antibodies to Brucella outer membrane lipoprotein was investigated in cattle and rams. Low but significant amounts of antibody were detected in sera from B. abortus-infected cattle and from B. ovis-infected rams which had developed epididymitis. Strain-19-vaccinated cattle also showed a weak albeit transient antibody response.