High species homology potentiates quantitative inflammation profiling in zebrafish using immunofluorescence

Due to substantial homology between the human and zebrafish genome and a high level of conservation of the innate immune system across species, zebrafish larvae have become an invaluable research tool for studying inflammation and modelling inflammatory disease. However, further microscopy techniques need to be developed for better profiling of inflammation and in particular, integrated cytokine responses to different stimuli - approaches are currently largely limited to assessment of changes in cytokine gene transcription and in vivo visualisation using transgenics, which is limited in terms of the number of cytokines that may be assessed at once. In this study, after confirming substantial homology of human vs zebrafish cytokine amino acid sequences, immunofluorescence staining using antibodies directed at human cytokines was performed. Inflammatory cytokine signalling responses to experimental tailfin transection was assessed over 24 h (1 hpi (hours post injury), 2 hpi, 4 hpi, 24 hpi) in zebrafish larvae, with experimental end point at 120 h post fertilization (hpf). When immunofluorescence results were compared to responses observed in rodent and human literature, it is clear that the cytokines follow a similar response, albeit with a condensed total time course. Notably, tumor necrosis factor-α and monocyte chemoattractant protein-1 increased and remained elevated over the 24-h period. In contrast, interleukin-1β and interleukin-6 peaked at 4 hpi and 2 hpi respectively but had both returned to baseline levels by 24 hpi. Macrophage migration inhibitory factor was lowest at 1 hpi, potentially encouraging macrophage movement into the site of injury, followed by a sharp increase. This protocol provides valuable insight into inflammation over a time course and more so, provides an affordable and accessible method to comprehensively assess inflammation in zebrafish disease models.