Neutrophils in Atlantic salmon (Salmo salar L.) are MHC class II+ and secret IL-12p40 upon bacterial exposure

Antigen-presentation via major histocompatibility complex (MHC) to T cells is the key event to initiate adaptive immune responses. In teleosts, as in mammals, the main types of professional antigen-presenting cells (APCs) are dendritic cells (DCs), monocytes/macrophages, and B cells. In the current study, flow cytometry, immunostaining and qPCR have been used to show that neutrophils in the teleost fish Atlantic salmon (Salmo salar L.) have antigen-presenting properties. The neutrophils were positive for MHC class II, CD83 and CD80/86, and upon in vitro bacterial exposure, gene expression analysis of purified neutrophils showed that IL-12p40, which is essential for proliferation of naïve T cells, was highly upregulated at both 6 and 24 h post bacterial exposure. Based on presence of MHC class II and upregulation of molecules involved in antigen presentation and T cell activation, we suggest that neutrophils in Atlantic salmon have potential to function as professional APCs. This work makes an important basis for further exploring the potential of using neutrophils to develop new, targeted immunoprophylactic measures.publishedVersio