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ABSTRACTPathogenically diverse Chlamydiaspp. can have surprisingly similar genomes. Chlamydia trachomatisisolates that cause trachoma, sexually transmitted genital tract infections (chlamydia), and invasive lymphogranuloma venereum (LGV) and the murine strain Chlamydia muridarumshare 99% of their gene content. A region of high genomic diversity between Chlamydiaspp. termed the plasticity zone (PZ) may encode niche-specific virulence determinants that dictate pathogenic diversity. We hypothesized that PZ genes might mediate the greater virulence and gamma interferon (IFN-γ) resistance of C. muridarumcompared to C. trachomatisin the murine genital tract. To test this hypothesis, we isolated and characterized a series of C. muridarumPZ nonsense mutants. Strains with nonsense mutations in chlamydial cytotoxins, guaBA-add, and a phospholipase D homolog developed normally in cell culture. Two of the cytotoxin mutants were less cytotoxic than the wild type, suggesting that the cytotoxins may be functional. However, none of the PZ nonsense mutants exhibited increased IFN-γ sensitivity in cell culture or were profoundly attenuated in a murine genital tract infection model. Our results suggest that C. muridarumPZ genes are transcribed—and some may produce functional proteins—but are dispensable for infection of the murine genital tract.

Chlamydia trachomatis genital infection is a worldwide public health problem, and considerable effort has been expended on developing an efficacious vaccine. The murine model of C. muridarum genital infection has been extremely useful for identification of protective immune responses and in vaccine development. Although a number of immunogenic antigens have been assessed for their ability to induce protection, the majority of studies have utilized the whole organism, the major outer membrane protein (MOMP), or the chlamydial protease-like activity factor (CPAF). These antigens, alone and in combination with a variety of immunostimulatory adjuvants, have induced various levels of protection against infectious challenge, ranging from minimal to nearly sterilizing immunity. Understanding of the mechanisms of natural infection-based immunity and advances in adjuvant biology have resulted in studies that are increasingly successful, but a vaccine licensed for use in humans has not yet been brought to fruition. Here we review immunity to chlamydial genital infection and vaccine development using the C. muridarum model.

ABSTRACTChlamydia trachomatisgenital infection is a worldwide public health problem, and considerable effort has been expended on developing an efficacious vaccine. The murine model of C. muridarumgenital infection has been extremely useful for identification of protective immune responses and in vaccine development. Although a number of immunogenic antigens have been assessed for their ability to induce protection, the majority of studies have utilized the whole organism, the major outer membrane protein (MOMP), or the chlamydial protease-like activity factor (CPAF). These antigens, alone and in combination with a variety of immunostimulatory adjuvants, have induced various levels of protection against infectious challenge, ranging from minimal to nearly sterilizing immunity. Understanding of the mechanisms of natural infection-based immunity and advances in adjuvant biology have resulted in studies that are increasingly successful, but a vaccine licensed for use in humans has not yet been brought to fruition. Here we review immunity to chlamydial genital infection and vaccine development using the C. muridarummodel.

ABSTRACTDespite effective antimicrobial chemotherapy, control of Chlamydia trachomatisurogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarummajor outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log10to 3 log10fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4+or CD8+T cells, and then challenged vaginally with C. muridarum. Depletion of CD4+T cells, but not depletion of CD8+T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log10to 4 log10more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log10to 3 log10decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4+T cells and antibody.

Despite effective antimicrobial chemotherapy, control of Chlamydia trachomatis urogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarum major outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log10to 3 log10fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4+or CD8+T cells, and then challenged vaginally with C. muridarum. Depletion of CD4+T cells, but not depletion of CD8+T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log10to 4 log10more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log10to 3 log10decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4+T cells and antibody.

Neoparamoebaspp. are amphizoic amoebae with the capacity to colonize the gills of some marine fish, causing AGD. Here, the gill tissue transcriptome response of Atlantic salmon (Salmo salarL.) to AGD is described. Tanks housing Atlantic salmon were inoculated with Neoparamoebaspp. and fish sampled at time points up to 8 days postinoculation (pi.). Gill tissues were taken from AGD-affected fish, and a DNA microarray was used to compare global gene expression against tissues from AGD-unaffected fish. A total of 206 genes, representing 190 unique transcripts, were reproducibly identified as up- or downregulated in response to Neoparamoebaspp. infection. Informative transcripts having GO biological process identifiers were grouped according to function. Although a number of genes were placed into each category, no distinct patterns were observed. One Atlantic salmon cDNA that was upregulated in infected gill relative to noninfected gill at 114 and 189 h pi. showed significant identity with the Xenopus, mouse, and human anterior gradient-2 (AG-2) homologs. Two Atlantic salmon AG-2 mRNA transcripts, designated asAG-2/1 and asAG-2/2, were cloned, sequenced, and shown to be predominantly expressed in the gill, intestine, and brain of a healthy fish. In AGD-affected fish, differential asAG-2 expression was confirmed in samples used for microarray analyses as well as in AGD-affected gill tissue taken from fish in an independent experiment. The asAG-2 upregulation was restricted to AGD lesions relative to unaffected tissue from the same gill arch, while p53 tumor suppressor protein mRNA was concurrently downregulated in AGD lesions. Differential expression of p53-regulated transcripts, proliferating cell nuclear antigen and growth arrest and DNA damage-inducible gene-45β (GADD45β) in AGD lesions, suggests a role for p53 in AGD pathogenesis. Thus AGD may represent a novel model for comparative analysis of p53 and p53-regulated pathways.

Neuronal cell death after DNA damage requires p53 and Bax, but the mechanism by which p53 activation leads to Bax translocation and cell death in neurons is not known. We report here that Peg3/Pw1 is up-regulated after DNA damage in cortical neurons in a p53-dependent manner. Overexpression of Peg3/Pw1 leads to decreased neuronal viability. The deleterious effect of Peg3/Pw1 on neuronal survival is abrogated by deletion of either p53 or Bax, indicating an essential role for both in Peg3/Pw1-mediated neuronal death. Moreover, overexpression of a Peg3/Pw1 dominant negative protein inhibits Bax translocation and neuronal cell death after DNA damage. These findings implicate Peg3/Pw1 as a mediator between p53 and Bax in a neuronal cell death pathway activated by DNA damage.