Immunohistochemical detection of IBV antigens in chicken embryos after experimental infection with IBV M41. (A) Proventriculus, focally extensive, there is strong immunolabelling of smooth muscle cells and scattered cells within the vasculature (arrows). Bar = 100 μm (B) Brain, within the cytoplasm of numerous neurons there is strong staining of IBV antigen. Bar = 40 μm (C) Spleen, scattered through the parenchyma there are numerous singular polygonal cells with red intracytoplasmic staining for IBV antigen, interpreted to be macrophages. Bar = 40 μm (D) Myocardium, capillary endothelium stains strongly positive for IBV antigen. Bar = 100 μm.