Immunohistochemical study on the relationship between doppel protein and bovine leukocytes.

Doppel (Dpl) is a prion-like protein whose sequence is notably similar to that of prion protein (PrP). Dpl is mainly expressed on testis and ovary and it is associated to neurodegeneration when ectopically expressed in transgenic mouse. PrP expression has been identified on tissue and blood leukocytes. Also Dpl has been detected on leukocytes located in germinal centers of lymphoid organs. Aim of this work is to immunohistochemically verify if also Dpl is expressed on leukocytes. This would help us to understand the biology and the mechanism of invasion of prion related protein. Samples of spleen and lymph nodes were collected from clinically healthy bovine at slaugthering. Tissues were frozen in liquid nitrogen. Cryostatic sections were stained by immunohistochemstry using the ABC technique: bovine Dpl was identified using a polyclonal antibody; leukocyte subsets were identified with monoclonal antibodies against the following antigens: CD1 (dendritic cells); CD4 (T4 cells); CD8 (T8 cells); CD11b (monocytes and granulocytes); CD11c (myeloid cells); CD14 (macrophages) CD21 (B cells); TCR / (T cell subpopulations); MHC II (activated leukocytes). Bovine Dpl was occasionally identified on spleen and lymph nodes. The distribution of the different leukocyte subsets in these organs, as defined by using the specific monoclonal antibodies, was normal: the Dpl-expressing leukocytes were morphologically identifiable as lyymphocytes and were localised at the periphery of germinal centers, where most of the lymphocytes were B-positive. The large part of the cells detectable on lymphoid organs, however, was Dpl negative. Based on their morphology, localisation and immunophenotype, the Dpl positive cells in spleen and lymph nodes might be interpreted as B lymphocytes. Nevertheless, most of the cells from lymphoid organs did not express, Dpl. This suggests that the positive cells might be derived from blood. The flow cytometric identification of Dpl on blood leukocytes is required to confirm this hypothesis.