Immunogene expression in head kidney and spleen of common carp (Cyprinus carpio L.) following thermal stress and challenge with Gram-negative bacterium, Aeromonas hydrophila

To evaluate the effect of thermal and microbial stress on the immune response of common carp (Cyprinus carpio L.), relative mRNA expression level of pro-inflammatory cytokines [tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-1 beta] and other genes related to immune or stress response [inducible nitric oxide synthase (iNOS), heat shock protein 70 (Hsp70), superoxide dismutase one (SOD1), and glucocorticoid receptor (GR)] was measured by quantitative PCR (qPCR). In addition, total protein and total immunoglobulin level in blood plasma of experimental common carp was also assayed. All the above parameters were estimated 24 h post-challenge with Gram-negative bacterium, Aeromonas hydrophila. Common carp (54.89 +/- 6.90 g) were initially exposed to 20 degrees C (control group) and 30 degrees C (thermal stress group) water temperature for 30 days, followed by experimental challenge with 2.29 x 10(8) colony forming unit/mL (CFU/mL; LD50 dose) of A. hydrophila. Exposure of fish to thermal stress and subsequently challenge with A. hydrophila significantly (P < 0.05) increases the IL-1 beta mRNA expression in head kidney and spleen of common carp by similar to 39.94 and similar to 4.11-fold, respectively. However, TNF-alpha mRNA expression in spleen decreased similar to 5.63-fold in control fish challenged with A. hydrophila. Thermal stress and challenge with bacterium suppresses the iNOS and GR mRNA expression in spleen of common carp. Moreover, significant (P < 0.05) increase in total protein content of blood plasma (similar to 43 mg/g) was evident in fish exposed to thermal stress and challenged with A. hydrophila. In conclusion, our study highlights the importance of elevated temperature stress and microbial infection in differential regulation of expression of several immunogenes in common carp.