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

Abstract

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.