Fourteen days later (Visit 2), a further venous blood


Fourteen days later (Visit 2), a further venous blood

sample was collected for post-vaccination serum antibody titres. Plasma leptin and serum neopterin were measured at MRC Human Nutrition Research, Cambridge UK. Leptin was measured by ELISA (R&D Systems, Abingdon, UK) and neopterin by a competitive enzyme immunoassay principle (BRAHMS Atiengesellschaft, Berlin, Germany). Both analytes were measured in duplicate and following manufacturers’ guidelines. Anti-Vi immunoglobulin G (IgG) analysis was conducted at the Laboratory of Developmental and Molecular Immunity, National Institutes of Child Health and Human Development, Bethesda, USA. Briefly, microtitre plates were coated with Vi (0.2 μg/well) purified from Citrobactor freundii and goat anti-human IgG (Jackson Immuno Research Laboratories Inc., West Grove, PA) conjugated to alkaline phosphatase were used for ELISA.

The anti-Vi IgG standard was a plasma sample from an adult vaccinated with Vi polysaccharide typhoid vaccine (provided by Wendy Keitel, Baylor University, Houston, TX). The Vi antibody content of this serum was also assayed by a radioimmunoassay (RIA) by Pasteur Merieux Connaught. The antibody levels were expressed in ELISA units (EU) and the reference sera were assigned a value of 75 EU. All samples were run in duplicate. Antibody levels were calculated using Program ELISA, version 12 (Center for Disease Control and Prevention, Atlanta, GA). Torin 1 mouse The lowest detectable level of the assay for anti-Vi IgG was 0.1 EU.

Prior to analysis, all data were log transformed, and results are presented as geometric means. For anti-Vi antibody levels, data are expressed as ELISA units (EU). Pneumococcal capsular polysaccharide specific IgG levels were measured at the WHO Pneumococcal Serology Reference Lab at the UCL Institute of Child Health, London, UK. Standard enzyme linked immunosorbent assay methods [11] were used to quantify anticapsular IgG antibodies to four specific many pneumococcal serotypes (1, 5, 14 and 23F). These serotypes were selected on the basis of frequency of carriage within this population setting, 14 and 23F being amongst the most common [12], and their importance in causing invasive disease (1 and 5 account for >40% in a recent series of pneumococci causing bacteraemia [13]). Comparisons amongst group means were made using two-sample t-tests. Vaccine data are presented as geometric means and 95% confidence intervals (CIs). Sex specific z-scores were calculated using UK reference data [14]. Associations between contemporary measures and antibody response to vaccination were compared by linear (for continuous variables) or logistic (for binary variables) regression analysis.

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