Chlamydia psittaci causes economic losses in chickens. There is no vaccine. We tested the recombinant major outer membrane protein (rMOMP) for vaccinating SPF chickens. Recombinant MOMP-His was prepared in transiently transfected COS-7 cells and purified using column chromatography. Seven day-old chickens were vaccinated by aerosol. Group 1 (n = 5) received 250µg rMOMP + ISCOMS per chicken and the control group 2 (n=7) received PBS + ISCOMS. Both groups were aerosol challenged at the age of 21 days with a highly virulent C. psittaci strain (106 TCID50). Clinical symptoms were scored every day. Pharyngeal and cloacal swabs were taken every other day post infection (p.i.) for monitoring bacterial excretion and blood was collected for IgM, IgG and IgA detection. At 3 weeks p.i., the birds were euthanized. Macroscopic lesions were scored. Tissue samples of the respiratory tract, liver and spleen were immersed in 4% formaldehyde for histopathology. Samples of the same tissues were used for Chlamydia antigen detection in frozen tissue sections. Proliferative responses of peripheral blood lymphocytes (PBLs) were determined at euthanasia.
Clinical symptoms were significantly more severe in the control group with all birds showing rhinitis, conjunctivitis and dyspnoea, whereas only 2 chickens of the vaccinated group had dyspnoea and 1 chicken showed rhinitis. Macroscopic lesions in all tissues of the control group were significantly more severe than the ones observed in the vaccinated group. Histopathological lesions were more pronounced in the control group. PBLs of the vaccinated group showed significantly higher proliferative responses than those of the control group. Results of bacterial excretion, antigen and antibody detection and identification of proliferating PBL (sub)populations will be presented. Preliminary results show that rMOMP vaccination reduced clinical symptoms and lesions following challenge with a highly virulent C. psittaci strain. Protection was associated with a superior T cell response upon challenge.