MHC class I (MHC I) and Lysozyme C (LYZ C) play important roles in disease resistance in fish species, and are thought to participate in anti-viral innate immunity. Previously, after Cyprinid herpesvirus 2 (CyHV-2) infection, MHC I and LYZ C were found to be expressed in both moribund (acute infection) and survivor (chronic infection) fish based on suppression subtractive hybridization (SSH) analysis. Herein, the complete open reading frames (ORFs) of MHC I and LYZ C were cloned from crucian carp (Carassius auratus gibelio). The full-length cDNAs of these two genes contained ORFs of 1,038 and 438 bp, and encoded polypeptides of 345 and 145 amino acids, respectively. Phylogenetic analysis indicated that MHC I and LYZ C were most closely related to the common carp. We found that the two genes were expressed at low levels in all tissues examined in healthy crucian carp. The mRNA expression levels of MHC I and LYZ C in crucian carp kidney tissues was monitored at different time points for 72 h after CyHV-2 infection using real-time RT PCR analysis. During CyHV-2 infection experiments, peak levels of MHC I were observed at 72 hpi (5.55-fold, P < 0.01), whereas 48 hpi (3.87-fold, P < 0.01) was the peak expression time point for LYZ C. By analysis of samples from both acute and chronic infection, the expression levels of MHC I and LYZ C were up-regulated in comparison to uninfected fish. These data suggested that MHC I and LYZ C are involved in cellular response to CyHV-2 infection. The discovery of LYZ C induced by CyHV-2 in crucian carp suggests its potential role in fish innate immunity against viral pathogen as MHC I.
2016 The Japanese Society of Fish Pathology