Pulmonary and systemic inflammation in a domestic animal model of respiratory chlamydophila psittaci infection: Evaluation of dose-response relationships

This study aimed to evaluate dose-response relationships of pulmonary and systemic inflammation with respect to a new model of respiratory Chlamydophila (C.) psittaci infection introduced recently. Four infection dosages (inclusion forming units of strain DC 15) were administered intrabronchially per calf: 10 6 (n = 4), 10 7 (n = 4), 10 8 (n = 4), 10 9 (n = 2). Control animals received medium (n = 4) or the inactivated strain (10 8 ; n = 6). Pulmonary inflammation was assessed by analysing broncho-alveolar lavage fluid (BALF) 2-3 days post inoculation (dpi). As biomarkers of systemic inflammation, acute phase proteins (LBP=lipopolysaccharide binding protein, Hp= haptoglobin, CRP) were measured in serum samples. Marker of pulmonary and systemic inflammation (Means) Controls Challenge with viable C. psittaci [ifu/calf] Medium Cp inactivated 10exp6 10exp7 10exp8 10exp9 BALF (2–3 dpi) Cell Count [G/L] 0.4 0.4 0.5 0.6 0.9 1.2 Granulocytes [%] 7 17 24 34 45 42 Macrophages [%] 90 80 72 62 52 45 Protein [μg/mL] 117 157 179 179 292 1019 Blood (2–3 dpi) LBP [μg/mL] 33 98 44 69 154 222 Hp [μg/mL] 66 175 637 843 311 62 CRP [μg/mL] 36 57 43 54 38 48 After challenge with viable chlamydiae, most of inflammatory markers followed dose-response curves (Table). In the lung, recruitment of neutrophil granulocytes increased with increasing doses. In blood, LBP was superior in reflecting host response. Conclusion: In conclusion, pulmonary and systemic inflammation varied from mild (10 6 ifu) to severe (10 9 ifu). For further studies, inoculation of 10 8 ifu per animal is recommended to induce a clinically apparent respiratory disease with local and systemic host responses.