Sequential skin lesions in chickens experimentally infected with Marek's disease virus

Skin biopsies taken at weekly intervals from the same specific-pathogen free (SPF) chickens inoculated with Md/5 Marek's disease virus revealed two distinctive patterns of perifollicular cutaneous lesions, tumour-associated and non-tumour-associated. The tumour-associated pattern was subdivided into two types. The progressive type was manifested by a continuous increase of lymphoid cell aggregates (LCA) in the skin, resulting in the development of gross skin tumours with or without visceral tumours, and the regressive type showed initially increased and finally regressed LCA in the skin, associated with the development of visceral tumours. The non-tumour-associated pattern was characterized by initial transient small LCA in the skin without evidence of tumour formation. Birds with the tumour-associated pattern, regardless of type, had persistent nuclear inclusions (NI) and positive reactions against MDV1-specific phosphorylated polypeptides in the feather follicle epithelium (FFE) and initial R1-type (consisting mainly of small lymphocytes with a few lymphoblasts) to advanced T-type (consisting predominantly of lymphoblasts) feather pulp lesions (FPL). On the other hand, birds with the non-tumour-associated pattern formed transient NI and positive reactions against MDV1-specific phosphorylated polypeptides in the FFE and Ri-type to R2-type (consisting mainly of plasma cells with oedema) FPL. Antigen-positive lymphoid cells against MDV1-specific phosphorylated polypeptides were detected in both inflammatory and tumourous lesions, especially in the necrotic tumour lesions in the skin of birds showing the progressive type.