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Chlamydia trachomatis is an obligate prokaryotic intracellular pathogen of humans that infects mucosal epithelial cells. Exposed domains of its major outer membrane protein (MOMP) are both serotyping and protective antigenic determinants. To identify these domains, we have cloned and epitope-mapped the genes of serovars A, C (C serogroup) and L2, B (B serogroup) with a panel of monoclonal antibodies (mAbs). Predominantly conserved regions of the genes of both serogroups are interspersed with four short variable domains (I-IV). Recombinant phage clones expressing specific MOMP antigenic determinants revealed that protective serotypespecific mAbs recognized epitopes in variable domains I and fl. Protective subspecies and serogroup-specific mAbs recognized overlapping determinants in variable domain IV near the C terminus. A nonprotective species-specific mAb mapped to an invariant peptide of nine residues contained within variable domain IV. In the intact chlamydial organism of serovar B, variable domains HI and IV were susceptible to proteolytic digestion, whereas both N and C termini were protected. These results suggest an arrangement of MOMP in the outer membrane in which three of the four variable domains are exposed to the outside and in which both N and C termini are presumably oriented toward the periplasmic space. This molecular analysis of MOMP antigenic determinants and their surface topology on intact chlamydiae will be useful toward the development of a recombinant subunit or synthetic chlamydial vaccine.

BackgroundDespite considerable progress in our understanding of land plant phylogeny, several nodes in the green tree of life remain poorly resolved. Furthermore, the bulk of currently available data come from only a subset of major land plant clades. Here we examine early land plant evolution using complete plastome sequences including two previously unexamined and phylogenetically critical lineages. To better understand the evolution of land plants and their plastomes, we examined aligned nucleotide sequences, indels, gene and nucleotide composition, inversions, and gene order at the boundaries of the inverted repeats.ResultsWe present the plastome sequences of Equisetum arvense, a horsetail, and of Isoetes flaccida, a heterosporous lycophyte. Phylogenetic analysis of aligned nucleotides from 49 plastome genes from 43 taxa supported monophyly for the following clades: embryophytes (land plants), lycophytes, monilophytes (leptosporangiate ferns + Angiopteris evecta + Psilotum nudum + Equisetum arvense), and seed plants. Resolution among the four monilophyte lineages remained moderate, although nucleotide analyses suggested that P. nudum and E. arvense form a clade sister to A. evecta + leptosporangiate ferns. Results from phylogenetic analyses of nucleotides were consistent with the distribution of plastome gene rearrangements and with analysis of sequence gaps resulting from insertions and deletions (indels). We found one new indel and an inversion of a block of genes that unites the monilophytes.ConclusionsMonophyly of monilophytes has been disputed on the basis of morphological and fossil evidence. In the context of a broad sampling of land plant data we find several new pieces of evidence for monilophyte monophyly. Results from this study demonstrate resolution among the four monilophytes lineages, albeit with moderate support; we posit a clade consisting of Equisetaceae and Psilotaceae that is sister to the "true ferns," including Marattiaceae.