Search

Abstract The complement system has important roles in both innate and adaptive host defense against invading microorganisms in vertebrates. The complement factor B (Bf), complements 2 (C2) and 4 (C4) can initiate and activate the complement system. In the present study, three complement genes, named as OnBf , OnC2 and OnC4 , were identified from Oreochromis niloticus , their distributions in host tissues and dynamic expressions after Gyrodactylus cichlidarum infection were investigated. The full-length cDNA of OnBf comprises an open reading frame (ORF) of 2055 bp, encoding a polypeptide of 684 amino acids which consists of two CCP modules at the N-domain, one VWA domain, and one Tryp_SPc domain at the C-terminal. The open reading frame (ORF) of OnC2 cDNA of 2385 bp encodes a protein of 794 amino acids with three (CCP) modules at the N-terminal, a less complex region, a VWA region, and a Tryp_SPc domain at the C-terminal. The full-length cDNA of OnC4 is comprised of an open reading frame (ORF) of 5082 bp encoding a polypeptide of 1693 amino acids which orderly includes A2M_N_2, ANATO, A2M, A2M_recep, C345C and three less complex regions. Quantitative real-time PCR (qPCR) analysis revealed that OnBf , OnC2 and OnC4 had higher levels of expression in the liver, stomach and spleen than in the tissues examined. After G. cichlidarum infection, the expression levels of OnBf , OnC2 , and OnC4 in the skin, liver, spleen and kidney were up-regulated at 2, 4, 6, 8, 10, 12 and 14 days, in general accordance with dynamics of prevalence and mean intensity, each showing an initial increase and subsequent decrease. These results might suggest that G. cichlidarum infection had induced a host immune response via OnBf , OnC2 , and OnC4. Highlights • The Bf/C2 and C4 genes were cloned and characterized from Oreochromis niloticus. • The expressions of Bf , C2 and C4 in different tissues of normal O. niloticus and those after Gyrodactylus cichlidarum infection. • After infection, the upgraded expression of immune related genes were consistent with trends of prevalence and mean intensity. • Gyrodactylus cichlidarum are preferentially located on the fins rather than on the body of Oreochromis niloticus. [ABSTRACT FROM AUTHOR]

Gyrodactylids mainly parasitizing on the skin and fins of fishes, represent an ongoing challenge of farmed fishes. Evidences from previous studies suggested that complement system play important role in fish against gyrodactylids. Through a series of parasite killing experiments with fish sera and mucus, the present study revealed the role of Oreochromis niloticus complement in killing Gyrodactylus cichlidarum. The killing effect on G. cichlidarum was observed in serum and mucus of O. niloticus , which was markedly weakened after the complement inhibition by heat treatment and C3 antibody neutralization. Scanning electron microscopy (SEM) revealed various injuries on the tegument of G. cichlidarum exposed to O. niloticus serum. After inhibiting the alternative complement pathway (ACP) by zymosan, the killing activity of O. niloticus serum to G. cichlidarum was significantly attenuated (P < 0.01). The inhibition (by adding EGTA or l -lysine) to the classical complement activation pathway (CCP) also resulted a weak suppression on the killing effect. The results demonstrated the indispensable role of O. niloticus complement in killing G. cichlidarum , mainly via the ACP and with the involvement of CCP as well. In addition, complement in serum of an unnatural host (Ctenopharyngodon idella) of G. cichlidarum showed highly significantly weaker killing effect to G. cichlidarum than that of O. niloticus (P < 0.01), which needs further study for its mechanism. These findings provided new evidences about the immune mechanism of fish against gyrodactylids, and are reference for the study on the control of gyrodactyliasis. • The complement in serum and mucus of Oreochromis niloticus displayed strong killing effect on Gyrodactylus cichlidarum. • The killing effect was mainly mediated by ACP, and CCPwas also involved. • The complement in serum of Ctenopharyngodon idella (non-host) showed weak killing effect to Gyrodactylus cichlidarum. [ABSTRACT FROM AUTHOR]

Nile tilapia, Oreochromis niloticus , is among the most preeminent aquaculture species in the world. In aquaculture systems, this species is vulnerable to various pathogens including Gyrodactylus cichlidarum (Monogenea). The major histocompatibility complex (MHC) genes, a highly polymorphic gene superfamily, have vital roles in adaptive immunity and are closely associated with disease resistance. In the present study, the relationship between MHC II α polymorphism of Oreochromis niloticus and the susceptibility to G. cichlidarum infection were analyzed. A total of 50 alleles of MHC II α were identified, which demonstrated a high level of polymorphism representing a variability of 89.6% amino acid sites. In the peptide-binding region (PBR) and entire region, the values of d N to d S were 1.155 and 1.180, respectively. Infection experiments revealed that hosts with moderate polymorphism of MHC II α (2 to 3 alleles) had relatively higher resistance to G. cichlidarum infection. In addition, the alleles Orni-DAA*0201 and Orni-DAA*0701 were found to be significantly associated with susceptibility (P < 0.05), while Orni-DAA*3601 was highly associated with resistance (P < 0.05). The results suggested that the diversity of MHC II α allele was associated with the susceptibility of tilapia to this monogenean, which would contribute to the study on MHC diversity maintenance and molecular-assisted selection of O. niloticus to enhance disease resistance. Of course, small scale of productive tests is required to further confirm these results. • Oreochromis niloticus has high level of polymorphism in Orni-DAA alleles. • The diversity of MHC II α in O. niloticus might be generated by positive selection, which was mediated by parasites. • Oreochromis niloticus with medium number of Orni-DAA alleles had higher resistance to Gyrodactylus cichlidarum infection. • The allele Orni-DAA*3601 was highly associated with resistance to G. cichlidarum infection, while Orni-DAA*0201 and Orni-DAA*0701 were significantly linked with susceptibility. [ABSTRACT FROM AUTHOR]

Gyrodactylus cichlidarum and Cichlidogyrus sclerosus , two monogenean ectoparasite species commonly found on the body surface and gills of Nile tilapia ( Oreochromis niloticus ) respectively, inflicted considerable economic losses in intensive tilapia farming. In order to explore the immune response of tilapia against these two species of monogeneans, expression patterns of five immune-related genes were studied after singular G. cichlidarum or C. sclerosus infection and their coinfection. The transcription levels of IL-1β were up-regulated in the skin after G. cichlidarum infection, reaching a peak at day 5 PI, and in the gills after C. sclerosus infection (peaking at day 8 PI), with significant elevation only detected in the gills after high-dose C. sclerosus infection. A trend favoring increased gill TNF-α expression at day 8 PI of C. sclerosus infection was statistically significant only in the low-dose infection group. TNF-α expression in the skin did not change significantly after G. cichlidarum infection. TGF-β had extremely up-regulated expressions in the gills at day 8 PI after both high- and low-dose C. sclerosus infections, but its significantly promoted expression in the skin was observed only after infection of high-dose G. cichlidarum . Significantly increased expressions of HSP70 and COX-2 in the skin were detected after high-dose G. cichlidarum infections. In comparison to singular infection with either G. cichlidarum or C. sclerosus , concurrent infection resulted in significantly advanced expression of TGF-β in both skin and gills, and lower expressions at day 8 PI, and similar patterns were observed in the expression of IL-1β and TNF-α in the gills. G. cichlidarum infection on the body surface significantly down-regulated the expressions of TNF-α, TGF-β and COX-2 in the gills. In addition, the intensity of G. cichlidarum was significantly positively correlated with that of C. sclerosus (correlation index 0.922, p = 0.000) at day 2 PI under concurrent infection. These results contribute to the understanding of mucosal immunity of fish against monogenean infection, particularly when two monogenean species infect concurrently. [ABSTRACT FROM AUTHOR]

Monogenean Gyrodactylus cichlidarum can cause severe mortality of Nile tilapia (Oreochromis niloticus) fry. To date, reports about mucosal immunity of O. niloticus against this parasite have been rare. In order to explore the mucosal immunity of Nile tilapia against G. cichlidarum infection, the expressions of six adaptive immune-related genes and the contents of specific immunoglobulin IgM and IgT in the skin-associated lymphoid tissues (SALT) were dynamically analyzed after primary and secondary infections. The abundances of G. cichlidarum on the hosts after secondary infection were lower than those after primary parasite infection, which implied that hosts could initiate immune protection against G. cichlidarum reinfection to some degree. The transcription levels of TCR-β and CD4 genes in the skin tissue were significantly up-regulated after primary G. cichlidarum infection, while genes pIgR and IgT were only detected with significant up-regulations during secondary infection. With the exception of pIgR, which had remarkably higher expression in the fish with low parasite loads, all other genes studied tended to have higher mRNA level in the fish with higher parasite loads. The specific IgM content in the skin mucus increased significantly on the 2nd day after the primary exposure, higher than the corresponding value during the secondary exposure, and had significantly positive correlation with the parasite loads during the first parasite infection. These results manifested that acquired immune responses in the SALT of Nile tilapia participated in the resistance against G. cichlidarum infection, underscoring the involvement of mucosal immunity in fish against monogenean infection, and suggesting potential prophylactic treatment of gyrodactylid disease of tilapia. • G. cichlidarum loads in reinfection were lower than those in primary infection. • Significant up-regulations of adaptive immune-related genes expressions were detected. • Specific IgM significantly increased and had positive correlation with parasite loads. [ABSTRACT FROM AUTHOR]