Modification of Helicobacter pylori outer membrane protein expression during experimental infection of rhesus macaques

Abstract

Clinical isolates of Helicobacter pylori show marked diversity, which may derive from genomic changes that occur during the often lifelong association of the bacterium with its human host. We used the rhesus macaque model, together with DNA microarrays, to examine genomic changes in H. pylori that occur early during experimental infection. Microarray analysis showed that H. pylori recovered from challenged macaques had deleted babA, a member of a large family of paralogous outer membrane proteins (OMPs) that mediates attachment of H. pylori to the Lewis B blood group antigen on gastric epithelium. In some cases the babA gene was replaced by babB, an uncharacterized OMP that is closely related to babA. In other cases the babA gene was present but was not expressed because of alteration in dinucleotide CT repeats in the 5 coding region. In either case, strains lacking babA did not adhere to Lewis B, which is expressed on macaque gastric epithelium. Absence of babA and duplication of babB was also seen in H. pylori isolates derived from human clinical samples, suggesting that this gene conversion event is not unique to experimentally infected rhesus monkeys. These results demonstrate in real time with a relevant animal model that H. pylori regulates OMP expression in vivo by using both antigenic variation and phase variation. We suggest that changes in babA and babB after experimental infection of macaques represent a dynamic response in the H. pylori outer membrane that facilitates adherence to the gastric epithelium and promotes chronic infection.

A mutation burst during the acute phase of Helicobacter pylori infection in humans and rhesus macaques

“…Similar to previous observation on J166 output strains from another macaque infection experiment 28 , the hopS (babA) gene was either replaced by the closely related OMP gene hopT (babB) by intra-chromosomal translocation or contained a frameshift mutation that was caused by an extra CT dinucleotide repeat unit in the 5 0 part of the hopS gene (Supplementary Tables 8-19). As was shown previously, either gene conversion or frameshift in the poly(CT) tract functionally inactivates babA, resulting in loss of adherence to the Lewis b blood group antigen on the gastric epithelium 28 . These changes in the H. pylori babA expression in mice and in monkeys typically occurred within the first 4-8 weeks 28,29 .…”

“…As was shown previously, either gene conversion or frameshift in the poly(CT) tract functionally inactivates babA, resulting in loss of adherence to the Lewis b blood group antigen on the gastric epithelium 28 . These changes in the H. pylori babA expression in mice and in monkeys typically occurred within the first 4-8 weeks 28,29 . In addition, the apparent loss of cag PAI function by frameshift mutations in the cagX and cagY genes ( Supplementary Fig.…”

Metastability of Helicobacter pylori bab adhesin genes and dynamics in Lewis b antigen binding

“…Chimeric babA͞B genes were found in a population genetic survey, although they were not very common (28). Derivatives of human H. pylori strain J166 with formally equivalent replacements of babA by babB were found as the most common monkey-adapted type after experimental infection of each of several rhesus monkeys (19). A few of the other J166 derivatives had lost Leb binding by slippage in a CT repeat that happens to occur in this particular strain's babA gene.…”

“…It is not known whether the adaptation of strain J166 to this primate model often involves selection against BabA, selection for elevated levels of BabB, or both. Assuming babB and babA each to be beneficial to H. pylori in particular hosts or stages of infection, the long-term survival of lineages in which particular bab genes have been lost by replacement, as witnessed here, and in strain J166 in monkeys (19) may depend on occurrence of at least transient mixed infection and reacquisition of lost bab genes by interstrain recombination.…”

“…For example, reference strain CCUG17875 (here denoted 17875) has two babA genes: babA2, from which the BabA adhesin is expressed, and babA1, which is silent because of an incomplete signal peptide (5). The babB gene is highly homologous to babA at its 5Ј and 3Ј ends but not at the central region that (in babA) determines the specificity of receptor binding (3,5,19). Other hop genes, babB included, contain repetitive sequence motifs that are prone to frameshift mutation and thereby metastable hop gene expression (17,18,20).…”