However, we found no differences in the patient characteristics between the groups with Ig titers of <40 AU and 40 AU (Table 2). Surprisingly, only 47% (33/70) of the patients responded with a 2-fold increase in Ig titer to their infective serotype, and as many as 24% (24/70) of the patients showed a decrease in Ig titer between paired sera (Ig titer ratio, <1;Table 2). old had a lower median Ig titer ratio than did younger patients (P< 0.031). The patients with serotypes with a thin capsule (1, 4, 7F, 9N, 9V, and 14) and medium/high invasive potential (1, 4, 7F, 9N, 9V, 14, and 18C) had higher Ig Maltotriose titer ratios than did patients with serotypes with a thick capsule (3, 6B, 11A, 18C, 19A, 19F, and 23F) and low invasive potential (3, 6B, 19A, 19F, and 23F) (P< 0.05 for both comparisons after adjustment for age). Ig titer ratios of <1 were predominantly noted in patients with serotypes with a thick capsule. In 8 patients with pneumococcal DNA detected in plasma, the three patients with Maltotriose the highest DNA load had the lowest Ig titer ratios. In conclusion, a high antibody response was associated with serotypes with a thin capsule and medium/high invasive potential, although a low antibody response was associated with serotypes with a thick capsule and a high pneumococcal plasma load. == INTRODUCTION == Streptococcus pneumoniaeis the most important cause Maltotriose of community-acquired pneumonia (CAP) in adults, and it is associated with significant morbidity and mortality (1). The pneumococcal capsule constitutes an important virulence factor and provides protection against the host immune response (2). More than 90 known encapsulated serotypes have been identified (3) based on the composition of their capsular polysaccharides (CPS). Pneumococcal infections show a broad spectrum of clinical presentations, from nasopharyngeal colonization to invasive pneumococcal disease (IPD), depending on host factors and the causative serotype (4). In vaccination studies, a significant type-specific antibody response has been found to confer protection against pneumococcal disease (57), but in studies with patients with pneumococcal infections, the anti-CPS antibody responses vary considerably (811). Therefore, the association between the immunogenicity of pneumococcal CPS and disease should be investigated further. Heavily encapsulated serotypes, as determined by fluorescein isothiocyanate (FITC)-dextran exclusion, were recently shown by Weinberger et al. (12) to be associated with resistance to neutrophil-mediated killing and an increased prevalence in nasopharyngeal carriage. Nasopharyngeal acquisition of pneumococci has been observed to generate elevated antibody levels in unvaccinated individuals (13,14). If the degree of encapsulation correlates with immunogenicity in pneumococcal disease, we hypothesized that that heavily encapsulated serotypes would induce higher antibody responses in pneumococcal pneumonia than would serotypes with a low degree of encapsulation. Furthermore, in a meta-analysis by Brueggemann et al. (15), an inverse correlation was found between carriage prevalence and the invasive potential for serogroups/serotypes, with the most prevalent carried serotypes being less likely to cause invasive disease. Thus, we hypothesized that serotypes with a low invasive potential induce a high anti-CPS antibody response in pneumococcal pneumonia, which protects against invasive disease. In this prospective study of adult patients with pneumococcal pneumonia, we aimed to study the anti-CPS antibody response to the causative pneumococcal serotype, with the serotypes grouped according to their degree of encapsulation and invasive potential. We also aimed to study if this antibody response is usually correlated with the pneumococcal DNA load in the bloodstream. (Data from the manuscript were presented at the ISPPD-8, Iquau Falls, Brazil, 11 to 15 March 2012, and at the 23rd European Congress of Clinical Microbiology and Infectious Diseases, Berlin, Germany, 27 to 30 April 2013.) == MATERIALS AND METHODS == == Study population and controls. == Between November 1999 and Rabbit Polyclonal to ECM1 April 2002, 235 adult patients with CAP admitted to the Department of Infectious Diseases at rebro University Hospital, Sweden, were enrolled in a prospective study. The inclusion criteria and population characteristics were described previously (16). CAP was defined as an acute onset of illness, with new radiological signs of pulmonary consolidation and 2 of the following signs or symptoms: fever of 38C, dyspnea, cough, pleuritic chest pain, or abnormal lung auscultation. During the same period, 113 adult controls were enrolled who were hospitalized for skin infections (n= 14), urinary tract infections (n= 14), arthritis or spondylitis (n= 6), or planned orthopedic or urologic surgery (n= 79) (16). None of the controls had been hospitalized for any reason during the preceding month or had received any antibiotic treatment during the preceding week..