The Mycoplasma hominis P120 membrane protein contains a 216 amino acid hypervariable domain that is recognized by the human humoral immune response

Abstract

The epitope for mAb 26.7D was mapped to the hypervariable domain by expression of various parts of this domain in Escherichia coli using expression vector systems. A polyclonal antiserum (pAb 121) generated against the hypervariable region of Pl20 from PG2l identified the Pl20 homologue in M. hominis PG21. Fusion proteins of the hypervariable and constant parts of the proteins were constructed and tested for reactivity with 21 human sera. Twelve sera reacted with the 7488 hypervariable fusion protein, but only four reacted with the PG2l hypervariable fusion protein. No reactivity was seen with a fusion protein containing part of the constant region of P120. Gene fragments amplified from 18 M. hominis isolates by PCR confirmed the heterogeneity of the hypervariable domain. Based on restriction endonuclease cleavage patterns of the hypervariable domain the 18 isolates could be divided into four classes. Reactivity with both mAb 26.71) and pAb 121 confirmed these classes. The hypervariable, but not the constant, part of PI20 was recognized by the human humoral immune response. Such a variable domain may be important in evasion of the host's immune response, and thus aid survival of the micro-organism.

Characterization of the variability of a 75-kDa membrane protein in Mycoplasma hominis

“…The isolates DC63/ 7488 were shown to have identical hypervariable domains in p120 [11]. These isolates were, in the present study, shown to be in di¡erent p75 RFLP groups.…”

“…Four isolates were, by DNA sequencing, found to have pairwise identical hypervariable domains; 7488/DC63 and SC4/P2. They were speculated to have arisen by horizontal gene transfer [11]. The Vaa protein has a modular composition.…”

Coupled Phase-Variable Expression and Epitope Masking of Selective Surface Lipoproteins Increase Surface Phenotypic Diversity in Mycoplasma hominis

“…We have shown in clinical isolate 1620 of M. hominis that (i) size variation of Vaa is caused by gain or loss of the tandem repetitive sequences in the central region of this protein; (ii) Cterminal sequence divergence of Vaa leads to antigenic variation among strains, as shown also by others in diverse isolates (2,6); and (iii) single-nucleotide insertions or deletions in a polyadenine tract within the 5Ј end of the vaa coding region create reversible frameshift mutations causing variable expression of Vaa, with concurrent alterations of M. hominis adherence to human cells in vitro (29). The abundant P120 surface lipoprotein contains a hypervariable N-terminal region, two central semivariable domains, and a highly conserved C-terminal region (3,12). The hypervariable domain of P120 is exposed on the mycoplasma surface and is the target of a strong humoral response in the human host, while the conserved C-terminal region is not.…”

“…Comparison of p120 alleles in different strains has revealed that P120 contains a hypervariable Nterminal region and a highly conserved C-terminal region (12). The hypervariable region of P120 is exposed on the mycoplasma surface and is immunodominant in the human host, while the highly conserved C-terminal region of P120 is apparently not a target of the humoral immune response.…”

“…The hypervariable region of P120 is exposed on the mycoplasma surface and is immunodominant in the human host, while the highly conserved C-terminal region of P120 is apparently not a target of the humoral immune response. Variable expression among M. hominis strains and antigenic variation related to the hypervariable region of P120 have been documented (12). However, high-frequency phase variation, requiring analysis of reversible switching in clonal populations, has not been previously demonstrated.…”