Using an artificial diet, composed of silt < 32 p in diameter and the alga Tetraselmis suecica, it was demonstrated that the oyster Crassostrea virginica could significantly reduce the concentration of algae voided in the pseudofaeces (measured as extracted chlorophyll pigment) by over 50 %, compared to levels in the food. More importantly, it was also shown that for C. virginica fed natural seston at concentrations between 4 to 20 mg I-', the proportion of energy, carbon and nitrogen voided in the pseudofaeces could also be reduced significantly compared to that in the food. As the organic material in natural seston is from a wide range of sources -e.g. phytoplankton of different sizes, bacteria, detritus particles, etc. -these results indicate that C. virginica has a well developed ability to ingest preferentially various types of organic material and to reject other particles as pseudofaeces. This discriminatory mechanism must be able to operate on individual particles despite the fact that they are bound in viscous mucus. We hypothesise (based on literature information for the properties of molluscan mucus) that the viscosity of the mucus in which the food particles are entrapped may be significantly reduced by the ciliary action on the ridged surfaces of the opposed labial palps. This reduced viscosity mucus is possibly moved to the free edge of the palp where, with a cessation of the mechanical stimulation, it regains its original viscosity. The individual particles may then be subject to chemical testing by chemoreceptors which determine whether a particle is moved over the palp ridge to the mouth or is admitted to the deep rejection tracts. These rejected particles move to the free edge of the palps where they are re-incorporated in the mucus and rejected as pseudofaeces.
Background Chlamydia trachomatis (CT) infection is the most prevalent bacterial sexually transmitted infection worldwide and, untreated, can lead to significant reproductive morbidity. Unfortunately, the prevalence remains high in the United States and no effective CT vaccine exists, in part because of an inadequate knowledge of immunological responses to CT infection in humans and, specifically, no correlates of protective immunity to guide vaccine studies. In animal studies, IFN-g and/or TNF-a producing CD4 cells are known to mediate protection against C. trachomatis. The objective of this study was to characterise the T-cell mediated immune responses to C. trachomatis in humans with and without CT reinfection at a follow up clinic visit. Methods In an ongoing study, peripheral blood mononuclear cells (PBMCs) are collected from CT-infected women at the time of treatment and stimulated in vitro with C. trachomatis antigens MOMP or PGP3, then fixed and permeabilized. The percentage of CD4 + and CD8 + T-cells expressing either IFN-g or TNF-a is then assessed using intracellular cytokine staining (ICCS) and flow cytometry. Women return at 3-and 6-months for repeat genital chlamydia screening. Cytokine-specific ICCS responses are then compared in women with versus without subsequent CT reinfection at follow-up to assess for possible correlates of protection.Results To date, we have performed ICCS on 44 women who have completed the study. Compared with women who had CT reinfection at a follow-up visit (n = 14), women without CT reinfection (n = 30) had higher baseline positive CD8 + TNF-a responses (p = 0.042). There was no significant association of IFN-g and/or TNF-a CD4 responses with CT reinfection risk. Conclusions Our preliminary findings reveal that a TNF-a-producing CD8 + T-cell response appears to correlate with a decreased risk for CT reinfection, suggesting a possible role in protective immunity. CD4 T-cell responses have not significantly differed in women with versus without CT reinfection.Introduction Chlamydia trachomatis causes two different sexually transmitted diseases: genital discharge (GD) and lymphogranuloma venereum (LGV). Apart from differences in tissue tropisms, little is known about differences in pathogenicity to the cells they infect, especially keratinocytes, the primary target of infection for LGV chlamydia. Methods Human keratinocytes (HaCaT cells), one LGV (serovar L2) and one GD (serovar E) isolate were used for all experiments with uninfected cells as the negative control. Experiments were performed at 37 and 33°C. For transmission electron microscopy (TEM) cells grown on Thermanox coverslips within 24-well plates were infected (MOI = 0.25) and incubated for various time-points over 48 h. The diameter of 15 mitochondria were measured in uninfected and infected cells at 1, 36 and 48 h post-infection using image analysis software. For the MTT assay cells grown in 96-well plates were infected (MOI = 0.25) and incubated for various time-points over 48 h. Median mitochondrial diameter wa...
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