Determination of the structure of the Escherichia coli K100 capsular polysaccharide, cross-reactive with the capsule from type b Haemophilus influenzae

Secretory IgA in Intestinal Mucosal Secretions as an Adaptive Barrier against Microbial Cells

Secretory IgA (SIgA) is the dominant antibody class in mucosal secretions. The majority of plasma cells producing IgA are located within mucosal membranes lining the intestines. SIgA protects against the adhesion of pathogens and their penetration into the intestinal barrier. Moreover, SIgA regulates gut microbiota composition and provides intestinal homeostasis. In this review, we present mechanisms of SIgA generation: T cell-dependent and -independent; in different non-organized and organized lymphoid structures in intestinal lamina propria (i.e., Peyer’s patches and isolated lymphoid follicles). We also summarize recent advances in understanding of SIgA functions in intestinal mucosal secretions with focus on its role in regulating gut microbiota composition and generation of tolerogenic responses toward its members.

IgA and the intestinal microbiota: the importance of being specific

Secretory IgA has long been a divisive molecule. Some immunologists point to the mild phenotype of IgA deficiency to justify ignoring it, while some consider its abundance and evolutionary history as grounds for its importance. Further, there is extensive and growing disagreement over the relative importance of affinity-matured, T cell-dependent IgA vs. "natural" and T cell-independent IgA in both microbiota and infection control. As with all good arguments, there is good data supporting different opinions. Here we revisit longstanding questions in IgA biology. We start the discussion from the question of intestinal IgA antigen specificity and critical definitions regarding IgA induction, specificity, and function. These definitions must then be tessellated with the cellular and molecular pathways shaping IgA responses, and the mechanisms by which IgA functions. On this basis we propose how IgA may contribute to the establishment and maintenance of beneficial interactions with the microbiota.

Escherichia coli BL21(DE3) chromosome contains a group II capsular gene cluster

During our study of de novo synthesis of Escherichia coli K1 capsular polysaccharides, we found that E. coli BL21(DE3) has a capsular gene cluster, similar to those of group II capsular E. coli strains. Analysis of the nucleotide sequence of the E. coli BL21(DE3) gene cluster showed homologues to all group II regions 1 and 3 genes and the presence of an IS1 element in one of the region 2 ORFs, which likely prevents capsule expression. Complementation analysis showed that region 1 and 3 genes encode functional proteins that are sufficient for the export of newly synthesized polysaccharide. The gene products of Bl21(DE3) kpsC and kpsS supported in vitro de novo synthesis of K1 polysaccharide when co-expressed with K1 NeuE and NeuS. Sequence homology between BL21(DE3) region 2 open reading frames and capsule-related genes in other bacteria such as Haemophilus influenzae serotype b, suggests that the encapsulated ancestor of BL21(DE3) may have produced a ribose/ribitol-phosphate containing polysaccharide.

Are anticapsular antibodies the primary mechanism of protection against invasive pneumococcal disease?

BACKGROUND

Antibody to capsular polysaccharide has been the basis of several vaccines that offer protection against invasive disease from Streptococcus pneumoniae. The success of such vaccines has led to the inference that natural protection against invasive pneumococcal disease is largely conferred by anticapsular antibody. If this is so, one would expect that the decline in disease from different serotypes would vary significantly, and that the appearance of substantial concentrations of anticapsular antibodies would coincide temporally with the decline in age-specific incidence.

METHODS AND FINDINGS

Using incidence data from the United States, we show that, on the contrary, the decline in incidence with age is quite similar for the seven most important serogroups, despite large differences in exposure in the population. Moreover, only modest increases in antibody concentration occur over the second and third years of life, a period in which serotype-specific incidence declines to less than 25% of its peak. We also present detailed data on the distribution of antibody concentrations in Israeli toddlers, which are consistent with the United States findings. The same conclusion is supported by new data on age-specific incidence in Finland, which is compared with published data on antibody acquisition in Finnish toddlers.

CONCLUSION

We suggest some additional studies of the mechanisms of protection that could distinguish among potential alternative mechanisms, including acquired immunity to noncapsular antigens, maturation of nonspecific immune responses, or changes in anatomy or exposure.

An NMR spectroscopic identity test for the control of the capsular polysaccharide from Haemophilus influenzae type b

We describe the use of Nuclear Magnetic Resonance (NMR) spectroscopy to control the identity of purified bulk capsular polysaccharide [called poly(ribosylribitolphosphate) or PRP] from Haemophilus influenzae type b (Hib), and derivatised forms, used in the production of Hib polysaccharide-protein conjugate vaccines. We describe the approaches we have developed to validate this test.

Degradation studies on Escherichia coli capsular polysaccharides by bacteriophages

The serologically and structurally related Eschrichia coli capsular polysaccharides (K antigens) K13, K20, and K23 were found to be depolymerized by the bacteriophages phi K13 and phi K20 to almost similar oligomer profiles as shown by polyacrylamide gel electrophoresis. The phage-polysaccharide interactions were followed by an increase of reducing 2-keto-3-deoxyoctulosonic acid due to a phage-associated glycanase that catalyzed the hydrolytic cleavage of common beta-ketopyranosidic 2-keto-3-deoxyoctulosonic acid linkages. The related E. coli K antigens K18, K22, and K100 as well as the Haemophilus influenzae type b capsular polysaccharide were degraded by bacteriophage phi K100 with different efficacy. It is suggested that phi K100 enzymatically cleaves ribitol-5-phosphate bonds as the only structural feature present in all the polysaccharides investigated.

Structure of the capsular antigen of Escherichia coli O8:K50:H-

The primary structure of the acidic capsular antigen of Escherichia coli O8:K50:H- was shown by glycose analysis, methylation analysis, and one- and two-dimensional 1H and 13C NMR spectroscopy to be composed of repeating linear tetrasaccharide units having the structure: (formula: see text).