Ox40 expression by T cells in NMO lesions. (A-C) Confocal microscopy of a perivascular early active NMO lesion stained with antibodies against Ox40 (A, red) and CD3 (B, green) (overlay C, yellow). The Ox40 antigen is expressed by a subset of T cells (white arrow). (D-F): Further stainings of NMO lesions with antibodies against Ox40 (brown) and CD8 (blue) (D-E) or CD4 (blue, F) reveals a complete absence of Ox40 expression on CD8+ T cells, both in perivascular lesions (D) and in the parenchyma at the edge of a demyelinating lesion (E). In contrast, Ox40 products are expressed by CD4+ T cells (purple), as seen in this perivascular lesion. Bars: 25 μm (A-C) and 50 μm (D-F).