NLR Family CARD Domain Containing5 (NLRC5) was identified as a transcription factor for MHC class- I gene expression . In this study, we used zebrafish as a model to study the function of nlrc5 under virus infections. Nlrc5 was knocked out from the zebrafish genome by CRISPR/Cas9 mediated gene editing and the complete absence of nlrc5 was confirmed in F2 homologs. We used the larval as well as adult zebrafish to understand the role of nlrc5. Either poly I:C or VHSV was administered intraperitoneally, organs were collected, and the gene expression was analyzed.
Immersion of the zebrafish larvae in poly I:C or VHSV (~108 TCID50/mL) did not alter the immune gene expression indicating that the zebrafish larvae are well protected by physical barriers from external stimulation . Microinjection of poly I:C into 5 dpf larvae did not alter the MHC class- I gene expression pattern between the nlrc5 KO and WT. In adult zebrafish, the spleen, blood, gills, and intestine had a considerable expression of nlrc5. Immune stimulation indicates the downregulation of MHC class-I genes in nlrc5 KO zebrafish (Figure A, B). VHSV titer (Figure C), disease pathology, and mortality were significantly higher in the nlrc5 ablated fish compared to the WT fish.
With our findings, we suggest that the zebrafish nlrc5 gene is important for the MHC class-I gene expression in adult zebrafish . Further studies on the role of the nlrc5 on the immune cell recruitment, and the antiviral defense is in-progress to fully unveil the role of this protein .