The VP7 structural protein is the most abundant of the major core proteins and is highly conserved in all serotypes of bluetongue virus (BTV). The aim of this study was to develop immunohistochemical techniques for the detection of BTV VP7 in Bouin's- and formalin-fixed and paraffin wax-embedded tissues from small ruminants (sheep and goats) naturally infected with BTV. Tissue samples were taken from animals in which BTV infection had been confirmed by reverse transcriptase polymerase chain reaction. Optimal results were obtained by incubation of monoclonal antibody 2E9 on samples fixed with Bouin's solution or neutral buffered formalin. Optimum antigen retrieval for Bouin's-fixed samples was by microwave heating (6 min) of tissue samples in citrate buffer (pH 6.0, 0.01 M), while for formalin-fixed samples a 30 min heating period in pH 9.0 buffer was required. In both species, BTV was mainly detected in the spleen, lymph nodes and lungs; specifically within the arteriolar and capillary endothelial cells, together with macrophages and lymphocytes. The immunohistochemical method described will be a useful tool for future research.
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