Antibody response of channel catfish after channel catfish virus infection and following dexamethasone treatment.

Channel catfish virus (CCV, Ictalurid herpesvirus 1) and CCV disease have been extensively studied. Yet, little is known about CCV-host interaction after resolution of the primary infection. In order to determine potential recrudescence of CCV from latency, we established latency by exposing channel catfish juveniles with CCV or a thymidine kinase-negative recombinant (CCVlacZ) at a dose that caused less than 20% mortality. Then, we evaluated antibody response by serially sampling the same fish at 0 (pre-infection), 30, 60 and 90 d post challenge (DPC). We then attempted to induce viral recrudescence by intramuscular administration of dexamethasone and sampled the fish at 2, 4, 7, or 10 d post treatment. Recrudescence was evaluated by leukocyte co-cultivation and cell culture of tissue homogenates but no virus was detected. Western blot data demonstrated the highest number of seropositive fish by 30 DPC and a secondary antibody induction after dexamethasone treatment. The antigen specificity of the secondary response corresponded to viral proteins with molecular masses similar to those recognized by the same fish by 30 DPC. The recognized proteins were predominantly large, ranging from approximately 90 to >200 kDa. Expression analysis of selected virus genes at 90 DPC and following dexamethasone treatment demonstrated occasional immediate-early virus gene expression in peripheral blood leukocytes. Early and late gene expression was rarely detected. The combined data suggest restricted re-activation of CCV in our experimental system. Primary and secondary responses and virus gene expression were demonstrated in CCVlacZ-exposed fish but were less frequent than in CCV-exposed fish.

Identification and expression analyses of poly [I:C]-stimulated genes in channel catfish (Ictalurus punctatus).

Channel catfish (Ictalurus punctatus) have proven to be an excellent model with which to study immune responses of lower vertebrates. Identification of anti-viral antibodies and cytotoxic cells, as well as both type I and II interferon (IFN), demonstrates that catfish likely mount a vigorous anti-viral immune response. In this report, we focus on other elements of the anti-viral response, and identify more than two dozen genes that are induced following treatment of catfish cells with poly [I:C]. We showed that poly [I:C] induced type I interferon within 2 h of treatment, and that characteristic interferon stimulated genes (ISGs) appeared 6-12 h after exposure. Among the ISGs detected by RT-PCR assay were homologs of ISG15, Mx1, IFN regulatory factor 1 (IRF-1), inhibitor of apoptosis protein-1 (IAP-1) and the chemokine CXCL10. Microarray analyses showed that 13 and 24 cellular genes, respectively, were upregulated in poly [I:C]-treated B cell and fibroblast cultures. Although many of these genes were novel and did not fit the profile of mammalian ISGs, there were several (ISG-15, ubiquitin-conjugating enzyme E2G1, integrin-linked kinase, and clathrin-associated protein 47) that were identified as ISGs in mammalian systems. Taken together, these results suggest that dsRNA, either directly or through the prior induction of IFN, upregulates catfish gene products that function individually and/or collectively to inhibit virus replication.