Bacterial infection triggers CD3εT cell expansion and interaction with macrophages in grass carp (Ctenopharyngodon idella).

Abstract

While T cells are well established as key players in mammalian adaptive immunity, their functional roles in teleosts remain poorly understood. Here, a monoclonal antibody against grass carp (Ctenopharyngodon idella) CD3ε was generated, and characterized by Western blotting, flow cytometry, and immunofluorescence. In healthy fish, CD3εT cells accounted for 5.1 %, 4.0 %, and 2.6 % of splenic, head kidney, and peripheral blood lymphocytes, respectively. Upon Aeromonas hydrophila infection, CD3εT cell populations elevated significantly in immune tissues such as spleen, head kidney, and posterior intestine, accompanied by upregulated transcription of T cell markers (Cd3ε, Tcr-β, and Lck). Strikingly, immunofluorescence analysis revealed that CD3εT cells and MCSFRmacrophages were located in the same region in the spleen tissue of A. hydrophila-infected fish, suggesting functional crosstalk between T cells and macrophages. Our findings provide the first evidence of T cell-macrophage interaction in teleost antibacterial defense, offering insights into the adaptive immune responses in fish.