Blood samples were stored overnight at RT and centrifuged (325 × g, 4 °C, 10 min) to collect serum. Nasal swabs and serum were stored at −20 °C until analysis (see Section 2.10). At the time of euthanasia (25 days PC) proliferative responses in peripheral blood lymphocytes were determined. All turkeys were examined for gross lesions. Macroscopic lesions were evaluated using the lesion scoring system previously described [2]. Samples of lungs, airsacs, trachea, conjunctivae, conchae, pericardium, spleen and liver were ON1910 imbedded in methocel, snap frozen in liquid nitrogen and stored at −80 °C until

preparation of cryostat tissue sections for the detection of chlamydial antigen. Cryostat tissue sections were analyzed by the IMAGEN™ direct immunofluorescence staining (Oxoid) [2]. Pharyngeal and cloacal swabs were examined for the presence of viable Cp. psittaci by culture in BGM cells [19]. The number of Cp. psittaci positive cells was counted in five randomly selected microscopic fields (Radiance 2000MP, Bio-Rad; 600×). A score from 0 to 5 was given for each swab or tissue individually. Score 0 means that there were no Cp. psittaci positive cells. Score MEK inhibitor 1 was given when a mean of 1–5 non-replicating elementary bodies was present. Scores 2–4 were given when a mean of 1–5, 6–10 and >10 inclusion positive cells could be observed. Score 5 meant that the monolayer was completely infected. Total IgG

(H + L) MOMP specific serum antibody titers were determined using a previously developed rMOMP ELISA [20]. Samples from SPF turkeys were used as negative controls and positive samples from previous vaccination experiments served as positive controls. Serum antibody titres were determined in 2-fold dilution series, starting at a dilution of 1/30, as were antibody isotypes (IgG-, IgM- and IgA) in serum (1/30 serum dilution), both as described before [2]. Total MOMP-specific antibodies and isotypes in nasal swabs were determined in undiluted samples using the same protocols as for antibody detection in serum. The results were presented as the OD measured at 405 nm ± the standard

deviation. At euthanasia, peripheral blood very lymphocytes (PBLs) were isolated from heparinised blood samples obtained by venipuncture (v. ulnaris). Lymphocyte proliferative tests were performed as described by Vanrompay et al. [21]. Briefly, rMOMP, medium (negative control) or concanavalin A (positive control) were added to the wells of a 96-well plate containing 6 × 105 cells. At day 6, cells were pulse-labelled with 3H-thymidine (1 μCi/well) (Amersham ICN, Bucks, UK) and 16 h later harvested onto glass fibre strips (Skatron, Lier, Norway). The radioactivity incorporated into the DNA was measured with a β-scintillation counter (PerkinElmer). The stimulation index (SI) was defined as the ratio of counts per min (cpm) of stimulated to medium-only stimulated cultures. At euthanasia, PBLs were isolated, stimulated and cultured as described in Section 2.11.