Changes in the distribution of cells expressing tumour-associated antigen in lymph nodes during the progression of enzootic bovine leukosis.

A monoclonal antibody (MAb), c143, that recognizes a tumour-associated antigen that is "upregulated" on neoplastic B cells in cattle with enzootic bovine leukosis (EBL), was used as a marker to study disease progression. An immunohistochemical examination of neoplastic tissue and superficial cervical lymph nodes from 14 animals with EBL revealed three morphologically definable stages of change in the structure of lymph nodes, associated with the distribution of c143-positive cells: (1) the presence of c143-positive cells at the marginal sinus with no apparent changes in lymph node structure; (2) the presence of positive cells extending into and distorting the architecture of the lymph node, with clear evidence of proliferation before overt changes (enlargement of lymph nodes) were evident; and (3) the presence of positive cells throughout the lymph node with total disruption of lymph node structure when clinical signs of lymph node enlargement were evident. The results indicated that the bovine leukaemia virus-transformed lymphocytes or neoplastic cells in peripheral blood accumulate in the marginal sinus area at the earliest stages, and subsequently proliferate and infiltrate into follicles, leading to the development of clinical signs of lymphosarcoma.