Fig. 4

Pathology of neutrophils and vacuolations in the E5415A model. Neutrophils and tissue vacuolation was strongly observed in the E5415A groups (0.1–1 mg), but never observed in the normal EAE, EAE with hIgG_cont, hIgG_NMO, and E5415A (0.01 mg) groups. Lesions were typically observed in a linear arrangement along radiating vessels and were diffusely present in the gray matter (a). The localization of neutrophils in the E5415A model (1 mg) is shown (b). The neutrophils were more abundantly present in the gray matter (GM) than in the white matter (WM) at spinal cord lesions (a, c), particularly at the lesion border (LB) (b). In the gray matter, the counts of neutrophils were significantly higher in the LB, than in the lesion core (LC) and normal appearance area (NAA) (c). Furthermore, there was a marked difference in tissue vacuolation in areas lacking AQP4 expression compared with NAA, statistically significant (d), particularly in the LC (b). The edges of these vacuoles were sometimes stained upon KB (f), MBP (g), or NF staining (h). KB staining was weak around the peri-vascular lesions, where foam-like vacuoles were found along with myelin debris (arrowhead) (f). Furthermore, some vacuoles included eosinophilic (e, arrowhead) and/or densely NF-positive distorted structures (h, arrowhead), suggesting degenerated and/or swollen fibers. These findings suggested the early active lesions with intra-myelinic edema and axonal injury. Scale bar = 100 μm (a), 40 μm (b), and 10 μm (e−h)