Identification and expression analysis of two CC chemokines in swordtail fish (Xiphophorus helleri) responses to Aeromonas hydrophila challenges

Chemokines are a large group of small proteins involved in migration, activation, and differentiation of leukocytes and are key regulators of the immune response and inflammatory response. In this study, we cloned and sequenced the cDNA of two CC chemokines (CCL4 and CCL19) from swordtail fish (X. helleri). The ORF-length of CCL4 is 294 nucleotides (nt) encoding a protein of 97 amino acids (aa), and the ORF-length of CCL19 is 333 nucleotides (nt) encoding a protein of 110 amino acids (aa). Quantitative real-time RT-PCR (qRT-PCR) analysis revealed both two CC chemokines were constitutively expressed in all tissues examined. The CCL4 was highly expressed in the spleen, lowly in the muscle and intestine; the CCL19 had the highest expression in the spleen and the relatively lower level in the heart. After challenge with bacteria, the CCL4 and CCL19 shared the same expression trend. In the spleen and liver, the mRNA level increased remarkably at 12 h, which suggested that the two CC chemokines may be involved in the X. helleri defense against A. hydrophlia infection. In summary, this study demonstrates the basic profiles of two CC chemokines in X. helleri and chemokines take an important part in inflammatory and immune responses to bacteria. Together, our results also indicate that the X. helleri could be utilized as a useful fish model for the research of fish diseases.