Advanced age does not diminish phagocytic activity or NET production in zebrafish (Danio rerio) kidney leukocytes

Abstract

Abstract The pace of growth in populations over the age of 65 is increasing in the U.S. and worldwide, posing serious challenges for health care systems. Studies in both humans and mice have revealed evidence of dysregulation of innate immunity in older individuals, although experimental systems and results of those studies vary widely. To explore whether the zebrafish (Danio rerio) model could be valuable in understanding the effects of aging on innate immune processes, we assessed phagocytic activity, respiratory burst response and neutrophil extracellular trap formation (NETosis) by anterior kidney phagocytes from healthy young (7–8 months old) and aged (>2.5 year old) zebrafish. Exposing leukocytes from transgenic mpx:GFP fish to opsonized pHrodo-labeled killed E. coli for 30 or 60 minutes revealed is no difference in the mean percentage of neutrophils that phagocytosed bacteria between the two ages at either time point. Interestingly, older fish displayed a wider range of responses and a higher level of individual variability than the younger population. Active neutrophils from the aged fish also exhibited a higher mean fluorescence intensity (MFI) than young fish at 30 min incubation, but fluorescence levels were similar in the two populations after 60 minutes of incubation. Leukocytes from older and younger wild type AB fish showed identical respiratory burst responses to PMA. When NET production was stimulated by calcium ionophore, neutrophils from aged AB zebrafish exhibited a higher NET index than the younger cohort. These initial results indicate that older zebrafish preserve a similar level of activity, if not hints of higher activity, in tested neutrophil functions compared to younger fish.