Flow cytometric analysis of skin blister fluid induced by mosquito bites in a patient with chronic active Epstein–Barr virus infection

In chronic active Epstein–Barr virus (EBV) infection (CAEBV), ectopic EBV infection has been described in T or natural killer (NK) cells. NK cell-type infection (NK-CAEBV) is characterized by large granular lymphocytosis, high IgE levels and unusual reactions to mosquito bites, including severe local skin reactions, fever and liver dysfunction. However, the mechanisms underlying these reactions remain undetermined. Herein, we describe a patient with NK-CAEBV whose blister fluid after mosquito bites was analyzed. The patient exhibited significant increases in the percentage of CD56⁺ NK cells in the fluid compared with a simple mosquito allergy, in which the majority of infiltrated cells were CD203c⁺ cells, indicating basophils and/or mast cells. His fluid also contained CD203c⁺ cells, and his circulating basophils were activated by mosquito extracts in vitro. These results suggest that CD203c⁺ cells as well as NK cells may play pathogenic roles in the severe skin reactions to mosquito bites in NK-CAEBV.