Decoration of lipopolysaccharide with phosphorylcholine: a phase-variable characteristic of Haemophilus influenzae

Abstract

Choline, although not a nutritional requirement for Haemophilus influenzae, is taken up from the growth medium and incorporated into its lipopolysaccharide (LPS). Incorporated choline is in the form of phosphorylcholine (ChoP) based on the reactivity with the monoclonal antibody with specificity for this structure, TEPC-15. Incorporation of [ 3 H]choline from the growth medium and expression of the TEPC-15 epitope undergo high-frequency phase variation, characteristic of other LPS structures in this species. The expression and phase variation of ChoP require a previously identified locus involved in LPS biosynthesis, lic1. The first gene in lic1, licA, contains a translational switch based on variation in the number of intragenic tandem repeats of the sequence 5-CAAT-3. The full-length LicA polypeptide resembles choline kinases of eucaryotes, suggesting that the pathway for choline incorporation into the H. influenzae glycolipid has similarities to the pathway for choline incorporation in eucaryotic lipid synthesis. The display of ChoP, a host-like structure, renders the organism more rather than less susceptible to the bactericidal activity of human serum. The increased serum sensitivity of variants with ChoP correlates with higher serum immunoglobulin G titers to LPS containing this structure. ChoP appears to be a cell surface feature common to a number of pathogens of the human respiratory tract, including Streptococcus pneumoniae and mycoplasmas. In the case of H. influenzae, its primary contribution to pathogenesis does not appear to be antigenic variation to evade host humoral clearance mechanisms.

Viral and Bacterial Interactions in the Upper Respiratory Tract

“…A third, well-described interaction mechanism involves phosphorylcholine, a cell-surface molecule that mediates bacterial adherence to host cell receptors. Phosphorylcholine is expressed by both S. pneumoniae [28] and H. influenzae [29], and seems to contribute to the competitive effect between these two species through its immunogenicity [30]. Pre-exposure to one of the two species induces the production of antibodies against phosphorylcholine, thereby promoting clearance of the other co-colonizing species [30,31].…”

“…Pre-exposure to one of the two species induces the production of antibodies against phosphorylcholine, thereby promoting clearance of the other co-colonizing species [30,31]. Since in vitro studies have shown that phosphorylcholine is necessary for the survival of pneumococci but not H. influenzae, the latter may switch off phosphorylcholine expression to give it an advantage over S. pneumoniae [29,31]. The host immune system is also involved in interspecies competition, as has been elegantly shown in vivo by Lysenko et al [32].…”

Structural analysis of the lipopolysaccharide oligosaccharide epitopes expressed by a capsule‐deficient strain of Haemophilus influenzae Rd

“…Subspectra corresponding to the individual glycosyl residues were identified on the basis of J-connectivity pathways delineated in the 1 H chemical shift correlation maps, the chemical shift values, and the vicinal coupling constants. 13 C resonances were assigned by heteronuclear 1 H± 13 C chemical shift correlation in the 1 H detected mode (HMQC) and the data are presented in Tables 3 and 6. The chemical shift data are consistent with each d-sugar residue being present in the pyranosyl ring form.…”

“…In accord, C-6 of Glc I in the LPS-OH and Fr. 1 oligosaccharides gave 13 (Table 4). In addition, the subspectrum of a b-linked GalNAc was recognized from the characteristic chemical shift values for H-2 (d 3.95) and C-2 (d 53.5) (Tables 4 and 6).…”

Diversity of mucosal immune responses in upper respiratory airways and the suitability of mucosal vaccines

“…As a nutritional requirement for S. pneumoniae, choline is taken up from the growth medium, and incorporated as PC into the capsular polysaccharide and cell membrane lipoteichoic acid [10]. Although not nutritionally required by H. influenzae, choline is incorporated into its lipooligosaccharide [11]. These findings suggest that PC is a vaccine candidate that is potentially protective against both S. pneumoniae and H. influenzae infections.…”