Immunity to Chlamydia psittaci with particular reference to sheep

Chlamydophila abortus infection in the mouse: a useful model of the ovine disease

Chlamydophila (C.) abortus is an obligate intracellular bacterium able to colonize the placenta of several species of mammals, which may induce abortion in the last third of pregnancy. The infection affects mainly small ruminants resulting in major economic losses in farming industries worldwide. Furthermore, its zoonotic risk has been reported in pregnant farmers or abattoir workers. Mouse models have been widely used to study both the pathology of the disease and the role of immune cells in controlling infection. Moreover, this animal experimental model has been considered a useful tool to evaluate new vaccine candidates and adjuvants that could prevent abortion and reduce fetal death. Future studies using these models will provide and reveal information about the precise mechanisms in the immune response against C. abortus and will increase the knowledge about poorly understood issues such as chlamydial persistence.

Toward chaperone-assisted crystallography: protein engineering enhancement of crystal packing and X-ray phasing capabilities of a camelid single-domain antibody (VHH) scaffold

A crystallization chaperone is an auxiliary protein that binds to a target of interest, enhances and modulates crystal packing, and provides high-quality phasing information. We critically evaluated the effectiveness of a camelid single-domain antibody (V(H)H) as a crystallization chaperone. By using a yeast surface display system for V(H)H, we successfully introduced additional Met residues in the core of the V(H)H scaffold. We identified a set of SeMet-labeled V(H)H variants that collectively produced six new crystal forms as the complex with the model antigen, RNase A. The crystals exhibited monoclinic, orthorhombic, triclinic, and tetragonal symmetry and have one or two complexes in the asymmetric unit, some of which diffracted to an atomic resolution. The phasing power of the Met-enriched V(H)H chaperone allowed for auto-building the entire complex using single-anomalous dispersion technique (SAD) without the need for introducing SeMet into the target protein. We show that phases produced by combining SAD and V(H)H model-based phases are accurate enough to easily solve structures of the size reported here, eliminating the need to collect multiple wavelength multiple-anomalous dispersion (MAD) data. Together with the presence of high-throughput selection systems (e.g., phage display libraries) for V(H)H, the enhanced V(H)H domain described here will be an excellent scaffold for producing effective crystallization chaperones.

Relative importance of CD4+ and CD8+ T cells in the resolution of Chlamydophila abortus primary infection in mice

The role of the specific cellular immune response is well established in Chlamydiaceae infections, but the importance of each T-cell subset seems to be species-dependent. This study was designed to clarify the role of T-cell subsets in the response to Chlamydophila abortus primary infection. C57BL/6 mice were depleted of CD4+ or CD8+, or both, by monoclonal antibody injections and subsequently infected with C. abortus. Mice were killed at intervals and samples were collected for bacteriological and histopathological analysis. Also carried out were spleen cell culture, cytokine quantification, immunolabelling for C. abortus antigen, and a TUNEL assay for apoptosis. CD8+ T cell-depleted mice all died within 12 days of C. abortus infection, while no mortality was observed in the other groups; surprisingly, CD4+ T cell-depleted mice showed lower morbidity (expressed as weight loss) than did a non-depleted (control) group. CD8+ T cell-depleted mice also differed from the other groups in showing a significantly higher chlamydial burden in the liver. CD8+ T cell-depleted mice also had a higher number of apoptotic cells in hepatic inflammatory foci and showed exacerbated IFN-gamma production by spleen cells after specific stimulation. Simultaneous depletion of both T-cell subpopulations led to a chronic infection, but not to early mortality. It is concluded that CD8+ T cells may play a role in the regulatory control of the CD4+ T-cell response and may have a direct cytotoxic or IFN-gamma-mediated effect on infected cells.

Immunopathology of Chlamydophila abortus infection in sheep and mice

Chlamydophila abortus targets the placenta, causing tissue damage, inflammation and abortion (enzootic abortion of ewes). It is one of the main infectious causes of abortion in ewes, resulting in major economic losses to agricultural industries worldwide. Although ruminants and pigs are the principal hosts, humans are also susceptible to infection. Control of disease requires a host inflammatory response, which is likely to contribute to pathology and abortion. Mouse models have been widely used to provide insight into the role of specific immune cells in controlling infection and disease. The use of such model systems for investigating the mechanisms of abortion, latency, persistence, and immunity to reinfection will result in the identification of novel vaccine control strategies for sheep.

Chlamydophila abortus (Chlamydia psittaci serotype 1) clearance is associated with the early recruitment of neutrophils and CD8(+)T cells in a mouse model

The immune mechanisms in response to Chlamydophila abortus (Chlamydia psittaci serotype 1) infection were studied in C57BL/6 and CBA mice. The infection was monitored and the following aspects of the immune response were evaluated: the nature of the leucocyte infiltrate in the liver, the percentages of polymorphonuclear neutrophils (PMNs), macrophages and lymphocytes in the spleen, and the concentrations of cytokines in serum. In addition, the serum concentrations of IgG1 and IgG2a were determined. Both mouse strains showed a Th1-like immune response, with high concentrations of IFN-gamma and minimal levels of IL-4; however, C57 mice differed from CBA mice in showing milder clinical signs and earlier resolution of infection. The greater ability of C57 mice than CBA mice to eliminate chlamydophilae was related to the establishment of an earlier innate immunity, based on a more pronounced PMN response, and on a greater presence of CD8(+)T cells.

Interferon-gamma mediates long-term persistent Chlamydia psittaci infection in vitro

The long-term anti-chlamydial effects of recombinant ovine interferon gamma (rOvIFN-gamma) were studied in ovine ST-6 fibroblasts infected with the S26/3 strain of Chlamydia psittaci. Chlamydial multiplication was assessed by enzyme-linked immunosorbent assay analysis of supernate lipopolysaccharide, titration of inclusion-forming units in culture supernates, and enumeration of inclusion bodies in cultured cells at 7-day intervals. Concentrations of 250 and 1000 U/ml of rOvIFN-gamma resulted in a microbistatic inhibition of C. psittaci growth, which appeared to become microbicidal when rOvIFN-gamma was maintained in the cultures for 14 days or more. There were no signs of C. psittaci multiplication when cultures were maintained in 25 or 100 U/ml of rOvIFN-gamma. However, subsequent removal of rOvIFN-gamma from these cultures resulted in a re-emergence of viable, infectious chlamydiae, which eventually killed all the fibroblasts. This re-emergence was more rapid in cultures initially treated with 25 U/ml of rOvIFN-gamma than in those treated with 100 U/ml.

Pathogenesis of Chlamydia psittaci infection in sheep: detection of the organism in a serial study of the lymph node

Sixteen sheep were inoculated subcutaneously over the left prefemoral lymph node with an abortifacient strain of Chlamydia psittaci. Groups of four animals were killed after 3, 6, 12 and 18 days. Four of eight sheep which received a control inoculum were killed on day 6 and four on day 18. The left and right prefemoral lymph nodes were removed and weighed and portions taken from each for examination by the polymerase chain reaction (PCR), by culture, and by histopathological and immunohistochemical methods. The left prefemoral lymph nodes enlarged after the injection of C. psittaci, with the group mean weight on day 6 being the greatest and that on day 18 being normal. Examination by "nested" PCR showed samples from these nodes to be positive, except for one animal killed on day 3 and one on day 12. Live organisms, however, were not cultured from any of the samples collected. C. psittaci antigen was detected immunohistochemically in three of four nodes on day 3, in each of four on day 6, and in two of four on both days 12 and 18. Nodes from the contralateral side remained normal, as did those from unchallenged control sheep, and no antigen or DNA was detected in them.

The development of proliferative responses of ovine peripheral blood mononuclear cells to Chlamydia psittaci during pregnancy

In vitro lymphoproliferative responses to Chlamydia psittaci elementary bodies were detected in the peripheral blood mononuclear cells of pregnant sheep infected with C. psittaci. These responses were suppressed in cells collected in the immediate peri-parturient period, but returned to levels significantly above background within 14 days. Infection also suppressed the lymphoproliferative response to the T-cell mitogen Con A until abortion or lambing, but did not affect the proliferative response to the B-cell mitogen LPS.

Serological evidence of the three chlamydial species in an aboriginal community in the Northern Territory

OBJECTIVE

To determine the pattern of seropositivity to the three species of Chlamydia in women and children from a single community.

DESIGN

Testing of blood samples obtained during a prospective study of mothers and infants. For each individual, the sample giving the highest titre of antichlamydial antibody was included in the analysis.

SETTING

The only health centre for a small rural community in the Top End of the Northern Territory. This served all 1200 or so residents, almost 95% of whom were Aboriginal.

PARTICIPANTS

Sixty-one pregnant Aboriginal women at routine antenatal clinic visits, and 114 of their children aged between one and six years at the time of sampling.

MAIN OUTCOME MEASURE

Specific IgG or IgM antibody to any of the three species of Chlamydia at titres > or = 32, as determined by micro-immunofluorescence.

RESULTS

IgG antibody to one or more chlamydial species was found in 83.6% of mothers and 42.1% of their children. IgM antibody was found in five mothers and four children, in each case against only one chlamydial species. IgG antibody to C. trachomatis was found in 55.7% of mothers and 28.9% of children, to C. pneumoniae in 59.0% of mothers and 19.3% of children, and to C. psittaci in 29.5% of mothers and 17.5% of children. Log linear modelling gave positive correlations between seropositivity for C. trachomatis and C. pneumoniae (chi 2 = 9, P < 0.01), and for C. trachomatis and C. psittaci (chi 2 = 15, P < 0.001). Cross-reactivity was more evident in children than in mothers.

CONCLUSIONS

This is the first Australian report providing serological evidence of exposure to the three chlamydial species in one community. The seropositivity patterns suggest complex interactions when all species are present.

Interactions of porcine lymphocytes with Campylobacter-like organism membranes purified from proliferative enteropathy

Peripheral blood mononuclear cells prepared from 6 healthy pigs and 6 pigs apparently affected by proliferative enteropathy were incubated with dilutions of a sonicate of purified Campylobacter-like organisms 872/87 prepared from a separate case of proliferative enteropathy. Incubations were carried out in RPMI 1640 medium, supplemented with foetal calf serum, L-glutamine, sodium pyruvate and 2-mercaptoethanol for 5 days, with relevant concanavilin A and medium controls. Marked stimulation of lymphocyte proliferation was clearly evident in samples prepared from the pigs apparently affected by proliferative enteropathy (peak stimulation index 4.4-13.2) compared to the healthy pigs (peak stimulation index 3.0). Diagnosis of proliferative enteropathy in these naturally derived cases was confirmed by a specific IgM indirect immunofluorescence assay. The results suggested that a specific antigen-related mitogenesis of blood lymphocytes occurs in pigs affected by proliferative enteropathy. This may have implications for immunization regimes.

Immune responses of the ovine lymph node to Chlamydia psittaci. A cellular study of popliteal efferent lymph

The popliteal efferent lymphatics were cannulated in sheep of two categories, seronegative or immune to Chlamydia psittaci. Following subcutaneous injection of live C. psittaci or control material into the draining area of the popliteal node, sequential samples of efferent lymph were collected and analysed. Both categories of sheep responded to C. psittaci with increased outputs of lymphocytes and blast cells. Numbers of blast cells rose both absolutely and as a proportion of the total. Plasmablasts increased in number only in seronegative sheep. Outputs of total T cells (CD5+), helper T cells (CD4+), cytotoxic/suppressor T cells (CD8+) and non-helper, non-suppressor T cells (T19) were maximal 4 and 7 days after challenge in immune and seronegative sheep, respectively. Proportionally, CD4+ T cells declined, CD8+ T cells increased and T19 cells were unaltered with time after infection. Chlamydial antigens could not be demonstrated in the cells of efferent lymph by an immunoperoxidase method. The results of this preliminary study show that both T and B cell responses are involved in immunity to C. psittaci.