Haemophilus influenzae type b lipooligosaccharide: stability of expression and association with virulence

Abstract

Spontaneous antigenic and phenotypic variations in the lipooligosaccharide (LOS) of two strains of Haemophilus influenzae type b (Hib) were previously shown to be associated with changes in virulence (A. Kimura and E. J. Hansen, Infect. Immun. 51:69-79, 1986). The goal of the present study was to define further the stability of LOS expression by this pathogen and the role of Hib LOS in virulence. Variation in LOS antigenic reactivity, as detected with LOS-specific monoclonal antibodies, was observed in 3 of 30 Hib strains after single-colony passage. When large numbers of individual colonies from seven other Hib strains were screened, however, spontaneous LOS antigenic variation was detected in all of the strains. Antigenic variation was not consistently associated with an altered LOS phenotype, as determined by sodium dodecyl sulfatepolyacrylamide gradient gel electrophoresis and silver staining of LOS preparations. Changes in the LOS antigenic phenotype were correlated with altered virulence potential in two strains. In these strains, acquisition of reactivity with certain LOS-directed monoclonal antibodies was associated with the synthesis of a highermolecular-weight LOS, enhanced virulence, and increased resistance to serum killing involving the classical complement pathway.

Identification of a new locus involved in expression of Haemophilus influenzae type b lipooligosaccharide

“…Hib strain DL180 was isolated from the cerebrospinal fluid of a child with Hib meningitis at Parkland Hospital, Dallas, Tex. The other 10 Hib strains used in this study have been described previously (5,6,9,11,12,20,31). The LOS antigenic characteristics of these 11 Hib strains are listed in Table 1.…”

“…Over the past few years, several genes involved in the biosynthesis of Hib LOS have been characterized (6,13,16,26,28,30,32), and some of these have been shown to be involved in expression of surface-exposed LOS epitopes. Four of these surface-exposed epitopes, defined by their reactivity with monoclonal antibodies (MAbs) 12D9, 6A2, 4C4, and 5G8 (9, 20), were first noted because of the correlation between phase variation of their expression and changes in the virulence potential of Hib (11,12). The spontaneous phase variation of the epitopes reactive with MAbs 12D9, 4C4, and 6A2 has been attributed to the presence of a repetitive DNA motif (5'-CAAT-3') located in the 5' region of some of the relevant genes; variable expression of these genes was directly correlated with the number of CAAT repeats (28).…”

“…All LOS antigenic group 2 strains express the MAb 4C4-reactive epitope, and some also express the MAb 5G8-reactive epitope. Moreover, expression of the MAb 5G8-reactive epitope is apparently dependent on expression of the MAb 4C4-reactive epitope (6,11,12,33). Phase variation of the former epitope occurs independently of phase variation of the MAb 4C4-reactive epitope and can affect the virulence of some Hib strains (11,12).…”

“…Moreover, expression of the MAb 5G8-reactive epitope is apparently dependent on expression of the MAb 4C4-reactive epitope (6,11,12,33). Phase variation of the former epitope occurs independently of phase variation of the MAb 4C4-reactive epitope and can affect the virulence of some Hib strains (11,12). In this report, we describe the cloning and characterization of a locus that is involved in expression of the MAb 5G8-reactive LOS epitope as well as the identification of a new repetitive DNA motif contained in this locus.…”

The position of phosphorylcholine on the lipopolysaccharide of Haemophilus influenzae affects binding and sensitivity to C‐reactive protein‐mediated killing

“…The first complete structural analyses of the H. influenzae oligosaccharide from wild‐type isolates have only recently been reported and comprise a limited spectrum of strains (Masoud et al ., 1997; Risberg et al ., 1997, 1999). Although the complete array of different oligosaccharide structures synthesized by H. influenzae is yet to be determined, structural analysis confirms earlier studies suggesting marked interstrain heterogeneity (Gulig et al ., 1987; Kimura et al ., 1987; Zamze and Moxon, 1987). This is because of variation in the composition and linkage of hexoses on extensions from each of three conserved heptose residues (I–III) attached in a chain to 3‐deoxy‐ d ‐manno ‐octulosonic acid (Kdo).…”