Kawasaki disease (KD) is a systemic vasculitis of unknown etiology which 
predominantly affects medium- and small-sized muscular arteries. Histopathologic 
studies of KD vasculitis lesions have demonstrated characteristic T cell 
infiltration and an abundance of CD8 T cells; however, the contribution of 
cytotoxic lymphocytes to KD vasculitis lesions has not been identified. Here, we 
histopathologically and immunohistochemically examined infiltrating inflammatory 
cells, particularly cytotoxic protein-positive cells, such as granzyme B cells 
and TIA-1 cells, in KD vasculitis lesions. Three autopsy specimens with 
acute-phase KD were observed and contained 24 vasculitis lesions affecting 
medium-sized muscular arteries, excluding pulmonary arteries. Infiltrating 
neutrophils in vasculitis lesions were evaluated by hematoxylin and eosin 
staining, and monocytes/macrophages and lymphocytes were evaluated by 
immunohistochemistry. The predominant cells were CD163 monocytes/macrophages and 
CD3 T cells. CD8 T cells, granzyme B cells, and TIA-1 cells were also observed, 
but CD56 natural killer cells were rare. To the best of our knowledge, the 
current study is the first histopathologic report confirming the infiltration of 
inflammatory cells with cytotoxic proteins in vasculitis lesions in patients 
with KD. Cytotoxic T cells may play a role in the development of vasculitis 
lesions in KD patients.