Breed-specific immune responses to Eimeria tenella infection in chickens of Bangladesh.

Indigenous chicken breeds in Bangladesh represent valuable genetic resources with resilience to infectious diseases; however, their breed-specific immune responses remain poorly defined. This study investigated cytokine-mediated immune responses in three native Bangladeshi chicken breeds (Deshi, Naked Neck, and Hilly) and one exotic commercial crossbred line, Sonali (widely used in Bangladesh), following experimental infection with 70,000 sporulated Eimeria tenella oocysts. Quantitative PCR was used to evaluate temporal expression of key cytokines (IL-2, IFN-γ, IL-12, IL-17A, IL-17F, IL-22, IL-10, TGF-β) and immune regulators (TLR-4, TLR-15, CTLA-4) at 6, 10, and 14 days post-infection (DPI), which corresponded to early invasion, active schizogony, and later stages involving repeated parasite life cycles. Distinct breed-specific immune patterns were observed. Deshi chickens exhibited a Th17-dominant response supported by Th1 activation, characterized by strong upregulation of IL-17A and IFN-γ at 14 DPI, along with balanced IL-10 expression, suggesting effective immune regulation and parasite clearance. Sonali chickens showed pronounced activation of innate immune receptors, particularly TLR-4 and CTLA-4, indicating strong early immune activation with variable cytokine modulation. Naked Neck chickens demonstrated moderate and balanced cytokine responses, while Hilly chickens exhibited dysregulated immune signaling, characterized by suppressed TLR-4 expression and elevated IL-12 levels, suggesting susceptibility to immune imbalance. Correlation and multivariate analyses revealed coordinated activation of Th1 and Th17 pathways and highlighted interactions between pro-inflammatory and regulatory cytokines. Principal component analysis clearly differentiated breeds based on cytokine expression profiles, indicating distinct immunological trajectories. These findings emphasize the importance of indigenous chicken breeds as genetic resources for disease resistance and provide insights for developing sustainable, breed-based poultry health strategies. To our knowledge, this is the first study to characterize breed-specific cytokine-mediated immune responses to E. tenella infection in indigenous chickens of Bangladesh.