A low level of naturally occurring antibodies associates with functional antibody deficiency.

Functional antibody deficiency is clinically assessed from antibody responses to vaccination. However, diagnostic vaccination is complex and may fail in practice. We hypothesized that the levels of naturally occurring antibodies against galactose-α-1,3-galactose (αGal) may represent alternative markers of functional antibody capacity. We included data from 229 patients with suspected primary immunodeficiency in a retrospective study. Antibody levels against αGal and twelve pneumococcal serotypes were determined with solid-phase immunoassays. Pneumococcal vaccinations and treatment with normal human immunoglobulin were assessed from medical records. Anti-αGal antibody levels correlated positively with anti-pneumococcal antibody levels measured before and after pneumococcal vaccination. Contrary to the anti-pneumococcal antibody levels, the anti-αGal antibody level showed potential for predicting subsequent immunoglobulin treatment - a marker of disease severity. Naturally occurring antibodies may reflect the functional capacity tested by diagnostic vaccination but add more useful clinical data. The clinical utility of this easy test should be evaluated in prospective studies.

The human natural anti-αGal antibody targets common pathogens by broad-spectrum polyreactivity.

Naturally occurring antibodies are abundant in human plasma, but their importance in the defence against bacterial pathogens is unclear. We studied the role of the most abundant of such antibodies, the antibody against terminal galactose-α-1,3-galactose (anti-αGal), in the protection against pneumococcal infections (Streptococcus pneumonia). All known pneumococcal capsular polysaccharides lack terminal galactose-α-1,3-galactose, yet highly purified human anti-αGal antibody of the IgG class reacted with 48 of 91 pneumococcal serotypes. Anti-αGal was found to contain multiple antibody subsets that possess distinct specificities beyond their general reactivity with terminal galactose-α-1,3-galactose. These subsets in concert targeted a wide range of microbial polysaccharides. We found that anti-αGal constituted up to 40% of the total antibody reactivity to pneumococci in normal human plasma, that anti-αGal drives phagocytosis of pneumococci by human neutrophils and that the anti-αGal level was twofold lower in patients prone to pneumococcal infections compared with controls. Moreover, during a 48-year period in Denmark, the 48 anti-αGal-reactive serotypes caused fewer invasive pneumococcal infections (n = 10 927) than the 43 non-reactive serotypes (n = 18 107), supporting protection on the population level. Our findings explain the broad-spectrum pathogen reactivity of anti-αGal and support that these naturally occurring polyreactive antibodies contribute significantly to human protective immunity.

Capsular Polysaccharide Expression in Commensal Streptococcus Species: Genetic and Antigenic Similarities to Streptococcus pneumoniae.

Expression of a capsular polysaccharide is considered a hallmark of most invasive species of bacteria, including Streptococcus pneumoniae, in which the capsule is among the principal virulence factors and is the basis for successful vaccines. Consequently, it was previously assumed that capsule production distinguishes S. pneumoniae from closely related commensals of the mitis group streptococci. Based on antigenic and genetic analyses of 187 mitis group streptococci, including 90 recognized serotypes of S. pneumoniae, we demonstrated capsule production by the Wzy/Wzx pathway in 74% of 66 S. mitis strains and in virtually all tested strains of S. oralis (subspecies oralis, dentisani, and tigurinus) and S. infantis Additional analyses of genomes of S. cristatus, S. parasanguinis, S. australis, S. sanguinis, S. gordonii, S. anginosus, S. intermedius, and S. constellatus revealed complete capsular biosynthesis (cps) loci in all strains tested. Truncated cps loci were detected in three strains of S. pseudopneumoniae, in 26% of S. mitis strains, and in a single S. oralis strain. The level of sequence identities of cps locus genes confirmed that the structural polymorphism of capsular polysaccharides in S. pneumoniae evolved by import of cps fragments from commensal Streptococcus species, resulting in a mosaic of genes of different origins. The demonstrated antigenic identity of at least eight of the numerous capsular polysaccharide structures expressed by commensal streptococci with recognized serotypes of S. pneumoniae raises concerns about potential misidentifications in addition to important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and for the pathogen. IMPORTANCE: Expression of a capsular polysaccharide is among the principal virulence factors of Streptococcus pneumoniae and is the basis for successful vaccines against infections caused by this important pathogen. Contrasting with previous assumptions, this study showed that expression of capsular polysaccharides by the same genetic mechanisms is a general property of closely related species of streptococci that form a significant part of our commensal microbiota. The demonstrated antigenic identity of many capsular polysaccharides expressed by commensal streptococci and S. pneumoniae raises important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and the pathogen.

Osteopontin enhances phagocytosis through a novel osteopontin receptor, the alphaXbeta2 integrin.

Osteopontin (OPN) is a cytokine with multiple functions, including immune defense mechanisms against invading microorganisms. OPN-deficient mice are impaired in clearing intracellular pathogens, suggesting an important role of OPN during phagocytosis, but it remains to be defined how OPN may enhance this innate immune process. Here, we demonstrate that OPN binds to monocytes, but not resting T cells, NK cells, or B cells, and mediates chemoattraction of IL-1-activated human monocytes. Moreover, OPN binds in a specific manner to all known serotypes of the two bacterial species Streptococcus agalactiae and Staphylococcus aureus and opsonizes these bacteria for phagocytosis. We identify the integrin alpha(X)beta(2) (CD11c/CD18), which is highly expressed on the cell surface of monocytes, as a novel OPN receptor. To eliminate the contribution from other molecular interactions between the bacteria and the phagocyte, we show that OPN-coated synthetic beads are phagocytosed in an alpha(X)beta(2) integrin-dependent manner. The ligand recognition does not involve the RGD motif previously reported to support binding of OPN to integrins. Taken together, these data identify the alpha(X)beta(2) integrin as a novel OPN receptor that is required for OPN-mediated phagocytosis, thereby elucidating an important mechanism of an innate immune function of OPN.

An easy method for detection of nasopharyngeal carriage of multiple Streptococcus pneumoniae serotypes.

In this paper, a simplified method for detection of pneumococcal carriage and for revealing the presence of several serotypes in a nasopharyngeal sample is evaluated. Enrichment broth was used for transportation and for the initial culturing of samples. All specimens were examined directly by the capsular reaction test for the presence of any of the 91 known pneumococcal serotypes. Sub-culturing on blood agar was used for isolation of the pneumococcal strains detected in the primary broth culture. A total of 693 nasopharyngeal swabs were obtained among children, their parents and employees in day care centres. Pneumococci were observed in 363 samples and 36 of these (9.9%) contained more than one serotype (multiple carriages). Two persons carried 3 different serotypes simultaneously. A significant increase in the positive sampling rate (5.8%) was achieved by using the simplified method compared to conventional streaking of the swabs directly on blood agar (p<0.0001).

Ascariasis is a zoonosis in denmark.

A preliminary epidemiological survey indicated an association between Ascaris infections in Danish patients and contact with pigs or pig manure. In the present study, we compared Ascaris worms collected from humans and Ascaris worms collected from pigs by amplified fragment length polymorphism (AFLP) analysis, a technique for whole-genome fingerprinting, and by PCR-linked restricted fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer region of nuclear rDNA. The AFLP data were analyzed by distance- and model-based clustering methods. These results assigned Ascaris worms from Danish patients to a cluster different from that for worms from humans in other geographic areas. In contrast, worms from humans and pigs in Denmark were assigned to the same cluster. These results were supported by the PCR-RFLP results. Thus, all of the examined Danish patients had acquired Ascaris infections from domestic pigs; ascariasis may therefore be considered a zoonotic disease in Denmark.

A unique variant of streptococcal group O-antigen (C-polysaccharide) that lacks phosphocholine.

Streptococcus mitis strain SK598, which represents a subgroup of biovar 1, possesses a unique variant of the C-polysaccharide found in the cell wall of all strains of Streptococcus pneumoniae and in some strains of S. mitis. This new variant lacks the choline methyl groups in contrast to the previously characterized forms of C-polysaccharide, which all contain one or two choline residues per repeat. The following structure of the repeating unit of the SK598 polysaccharide was established: where AAT is 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose. This structure is identical to the double choline-substituted form of C-polysaccharide, except that it is substituted with ethanolamine instead of choline. This extends the number of recognized C-polysaccharide variants to four.