Immune responses of turkey poults with turkey poult enteritis

A turkey coronavirus (TCV) isolate associated with turkey poults with acute enteritis was identified and characterized by morphological, serological, and, molecular properties. Sephacryl S-1000 size-exclusion chromatography was found to be a useful method for purification of TCV from turkey embryo intestines. However, results of antibody-capture enzyme-linked immunosorbent assay (ELISA) coated with TCV antigens prepared from infected intestines were inconsistent. Alternatively, chicken infectious bronchitis coronavirus (IBV) was used as coating antigen for the antibody-capture ELISA based on the observed cross antigenicity between TCV and IBV. The established ELISA system was useful for diagnosis of turkeys infected with TCV as well as for evaluation of specific antibody responses of turkeys following experimental infection. Parameters for turkey lymphocyte proliferation responses to concanavalin A (Con A) were established for evaluation of T cell functional status of turkeys following experimental infection. Both humoral and cellular immunities were activated in turkeys infected with TCV. The humoral immunity was stimulated as indicated by the observations of TCV-specific antibody isotype responses and enhanced antibody response to sheep red blood cells. The cellular immunity was stimulated as indicated by the detection of TCV-specific lymphocyte proliferation response, increased lymphocyte proliferation responses to Con A, and enhanced proportions of CD4+ cells. Negative correlations between the activations of immune responses and the presence of TCV in the intestine were observed. Experimental suppression of B cell activity by cyclophosphamide enhanced severity of TCV infection. These results indicate that both humoral and cellular immunities of turkeys are activated following infection of turkey poults with TCV and humoral immunity may provide immunological protection for turkey poults against infection with TCV