Table 1.

Effects of gene diversity in chlamydial proteins on disease severity and tissue tropism.

Gene family	Gene name	Locus	Function/role	Effect on tissue tropism	Potential effect on disease severity
Omp family	omp A	ct681	Most prominent outer membrane protein; porin; antigen-variants	Classification of Chlamydia trachomatis serovars into A–K and LGV	No correlation between ompA and disease severity demonstrated
Pmp family	pmp A	ct412	Type V secreted proteins: some members (D, E, G and H) are expressed on the EB surface. PmpD, D and G elicit a strong inflammatory response. All of these proteins likely play a role in phase variation	Unknown	High variability of pmp genes by SNPs, gene duplication and indel mutations may be significant in contributing to disease severity
	pmpB	ct413		Specific amino acid substitutions distinguish LGV from non-LGV; difference in C. trachomatis E and F to other genital serovars
	pmpC	ct414		Specific amino acid substitutions distinguish LGV from non-LGV; difference in C. trachomatis E and F to other genital serovars
	pmpD	ct812		Specific amino acid substitutions distinguish LGV from non-LGV
	pmpE	ct869		Specific nucleotide substitutions segregate ocular from urogenital and LGV; difference in C. trachomatis E and F to other genital serovars
	pmpF	ct870		Specific nucleotide substitutions segregate ocular from urogenital and LGV
	pmpG	ct871		Specific amino acid substitutions distinguish LGV from non-LGV
	pmpH	ct872		Specific nucleotide substitutions segregate ocular from urogenital and LGV; difference in C. trachomatis E and F to other genital serovars
	pmpl	ct874		Difference in C. trachomatis E and F to other genital serovars
	tarp	ct456	Binds to actin, phosphorylated by host kinases; cytoskeleton rearrangement; involved in internalization	Number of actin-binding sites differentiate LGV and non-LGV; number of actin-binding sites important for tropism?	Number of actin-binding sites important for disease severity?
Inc proteins	incD	ctll 5	Sphingolipid transport; interacts with CERT	Mutations in incD specific to ocular and LGV tissue tropism	Unknown
	incE	ct116	Unknown	Unknown	Unknown
	incF	ct117	Unknown	Unknown	Unknown
	incG	ctll8	Blocks release of cytochrome C and inhibits apoptosis	Unknown	Unknown
	incA	ct119	Homotypic fusion of intracellular inclusions	In LGV the genetic variation of incA may reflect tissue tropism	Nonfusogenic clinical isolates have less severe clinical signs
		ct229f †	Modulation of inclusion trafficking; binds to Rab4A	Unknown	Unknown
	incB	ct232	Unknown	Unknown	Unknown
	incC	ct233	Unknown	Unknown	Unknown
	aaxB	ct373	AAX: arginine decarboxylase proenzyme; inhibits host cell polyamine synthesis, or inhibition of nitric oxide synthesis?	Unknown	Unknown
	aaxC	ct374	AAX: cytoplasmic arginine:agmatine antiporter; inhibits host cell polyamine synthesis, or inhibition of nitric oxide synthesis?	Unknown	Unknown
	trpA	ct171	Subunit of Trp synthase, which produces Trp from indole	Mutations in trpA segregate ocular from genital isolates	Unknown
		ct166f	Toxin-like protein; glycosylates Rac1; causing actin reorganization	Contains serovar specific loci, missing in LGV strains; potential role in invasiveness?	Potentially plays a role in disease severity (LGV strains lack the cytotoxin)

^†These loci have not, as yet, been named.

AAX: Arginine:agmatine exchange system; EB: Elementary body; Indel: Insertion and deletion; LGV: Lymphogranuloma venereum; SNP: Single nucleotide polymorphism.