Modulation of Master Transcription Factor Expression of Nile Tilapia Leukocytes via Cholinergic Pathways

Teleost fish are the first evolutionary group to exhibit an innate and adaptive immune system. Within the mechanisms of adaptive immunity, fish possess, among others, T-helper cells (CD4-like) and their differentiation machinery, regulated by the master transcription factors T-bet, GATA3, Foxp3, and RORγ. Many studies support the existence of a non-neuronal cholinergic system involved in the immune response, named after the ability of leukocytes to synthesize de novo acetylcholine (ACh). Organophosphorus pesticides (OPs), such as diazoxon (DXN), are examples of compounds that act as cholinergic disruptors with immunotoxic effects. The present study aimed to evaluate the expression of transcription factors in leukocytes (spleen mononuclear cells, SMNCs) of Nile tilapia by modulating cholinergic pathways in immune cells using agonists, antagonists, and diazoxon (DXN), an anticholinesterase substance. The obtained data showed a significant increase in RORγ mRNA expression upon stimulation with the nicotinic agonist, whereas activation of the muscarinic receptor with its agonist increased T-bet mRNA expression. An alteration in RORγ expression levels induced by DXN exposure was also observed. The results suggest a probable directing of the immune response towards a pro-inflammatory profile orchestrated mainly by RORγ and T-bet transcription factors in response to cholinergic stimuli.