In vivo exposure to microorganisms resident in the oral cavity is considered as a possible cause of Kawasaki disease (KD), and some epitopes derived from streptococci display homology with Factor H of Complement. Additionally, calprotectin, a major calcium binding protein released by neutrophils and activated monocytes, could be directly involved in endothelial damage occurring in KD. The aim of our study is to evaluate the percentages of IFN-y+ and/or TNF-a+ lymphocytes and double positive calprotectinffNF-a monocytes (CD14+) after in vitro stimulation with streptococcal-and/or Factor H-derived peptides, in patients with acute KD. Peripheral Blood Mononuclear Cells (PBMCs) obtained from KD patients and febrile controls were stimulated in vitro with peptides. After culture, cells were collected, stained with fluorochrome-labelled monoclonal antibodies against CD3, CD14, calprotectin, IFN-y and TNF-a, and cytofluorimetric analyses were performed. Our results showed increased percentages of TNF-a+IIFN-y+ lymphocytes in KD patients in respect to controls when PBMCs were stimulated with streptococcal or Factor H-derived epitopes. In addition, also calprotectin+rrNF-a+ monocytes from KD patients were activated after PBMC in vitro stimulation. These findings lead us to speculate that some peptides, derived from oral streptococci and cross-reactive with the human Factor H of Complement, could induce lymphocyte and monocyte activation potentially involved in the pathogenesis of KD. Our results should be confirmed by further studies enrolling more patients and controls than those analyzed in our study.Kawasaki disease (KD) is an acute febrile illness that primarily arises in infancy and early childhood characterized by diffuse vasculitis of medium-sized arteries. Clinical features consist of fever accompanied by lymphadenopathy, skin rash, conjunctivitis, oropharyngeal mucosal changes and extremity changes (l). Diagnostic criteria, used in clinical approach to patients may, however, be inadequate, and early diagnosis frequently remains challenging, with high risk of coronary damage. In fact, in most cases it is a limited illness resolving in few days after fever onset, but without appropriate intervention coronary artery aneurysms can develop in about 15-25% of the patients (1). The acute phase of KD is characterized by a deficiency of suppressor T cells, marked activation of the immune