OX-42 immunohistochemistry during symptomatic phase of disease. A, low power view reveals intensified immunoreactivity in spinal cord ventral horns; multiple large, rounded spots are visible. B, higher power view of large immunoreactive spots is suggestive of phagocytic clusters. C, same field as in B; counterstaining with cresyl violet facilitates identification of large immunoreactive spots as multinucleated giant cells. D, E, the same microscopic field prior to and after cresyl violet counterstaining reveals a well-formed multinucleated giant cell of the Langhans type. F, enlargement of framed area in C shows apoptotic microglial nucleus (arrow) within a giant cell. Scale bars: 500 μm (A), 40 μm (B, C), 20 μm (D-F).