Exaggerated pro-inflammatory reactions during the acute phase of Kawasaki disease (KD) suggest the role of immune dysregulation in the pathogenesis of KD. We investigated the profiles of T regulatory cells and their correlation with the clinical course of KD.

Peripheral blood mononuclear cells were collected from 17 KD patients during acute febrile and subacute afebrile phases. T cells expressing CD4, CD25, and Foxp3 were analyzed using flow cytometry, and the results were correlated with the clinical course of KD.

The percentage of circulating CD4⁺CD25^highFoxp3⁺ T cells among CD4⁺ T cells was significantly higher during the subacute afebrile phase than during the acute febrile phase (1.10%±1.22% vs. 0.55%±0.53%, P =0.049). Although levels of CD4⁺CD25^lowFoxp3⁺ T cells and CD4⁺CD25^-Foxp3⁺ T cells were only slightly altered, the percentage of CD4⁺CD25⁺Foxp3^- T cells among CD4⁺ T cells was significantly lower during the subacute afebrile phase than during the acute febrile phase (2.96%±1.95% vs. 5.64%±5.69%, P =0.036). Consequently, the ratio of CD25^highFoxp3⁺ T cells to CD25⁺Foxp3^- T cells was higher during the subacute afebrile phase than during the acute febrile phase (0.45%±0.57% vs. 0.13%±0.13%, P=0.038).

Decreased CD4⁺CD25^highFoxp3⁺ T cells and/or an imbalanced ratio of CD4⁺CD25^highFoxp3⁺ T cells to CD4⁺CD25⁺Foxp3^- T cells might play a role in KD development. Considering that all KD patients were treated with intravenous immunoglobulin (IVIG), recovery of CD4⁺CD25^highFoxp3⁺ T cells during the subacute afebrile phase could be a mechanism of IVIG.