University of Tehran Iranian Journal of Veterinary Medicine 2251-8894 19 1 2025 01 01 Role of Tumor Necrosis Factor-α in Experimental Streptococcus pneumoniae Infection in Lambs 11 22 100614 10.32598/ijvm.19.1.1005527 EN Abbas Abedulyemah Hamza Department of Pathology and Poultry diseases, College of Veterinary Medicine, University of Baghdad, Baghdad , Iraq. Zainab Ismail Ibrahim Department of Pathology and Poultry diseases, College of Veterinary Medicine, University of Baghdad, Baghdad , Iraq. Journal Article 2024 02 27 <strong>Background</strong>: Streptococcus pneumoniae is a common bacterial pathogen causing various diseases in humans and animals. <br /><strong>Objectives</strong>: We aimed to evaluate the role of tumor necrosis factor (TNF)-α against infection with Streptococcus pneumoniae by intratracheal route in lambs as an experimental animal model. <br /><strong>Methods</strong>: Six male un-weaned lambs, aged 1 to 2 months and weighing 5 to 7 kg, were exposed to S. pneumoniae strain ATCC 6303 serotype 3 at 2×106 CFU/mL via intratracheal route to induce pneumonia. Pneumonic clinical signs were monitored daily, and blood samples were collected before exposure (day 0) and on days 3, 6, and 14 post-exposure for total and differential white blood cells (WBC) counts and TNF-α assessments. Additionally, on days 6 and 14 post-exposure, trachea and lung tissue samples were collected for macroscopic and microscopic pathological evaluation.<br /><strong>Results</strong>: The findings revealed a significant increase (P<0.001) in total WBC counts from day 3 post-exposure, maintaining elevated levels on days 6 and 14 compared to day 0. Differential WBC counts indicated an early, significant rise in neutrophils, with sustained elevation in lymphocytes and monocytes. TNF-α levels peaked on day 3 and gradually declined by day 14 post-exposure, reflecting an acute inflammatory response to the infection. Gross pathology at 6-14 days post-exposure showed pulmonary congestion and edema of affected lungs, emphysema, swelling, and congestion of the trachea. Histopathologically marked epithelial degeneration and necrosis with inflammatory processes in tracheitis and focal interstitial pneumoniae.<br /><strong>Conclusion</strong>: The present study concluded the pivotal role of TNF-α in the immune response against S. pneumoniae infection in lambs.  https://ijvm.ut.ac.ir/article_100614_4782602bf72cb642cec938b422ee3ec6.pdf