Text Box: EXPRESSION OF CD19,CD23 ON PERIPHERAL BLOOD MONONUCLEAR CELLS (PBMC) FROM CHILDREN WITH INFECTIOUS MONONUCLEOSIS Luo XM, Zhou FY, Zhou YL, Wang XX, Qiu LN Zhejiang People¡¯s Hospital, Hangzhou, China Objective: To explore the action of B cells in the patients with IM Methods: The study group comprised 17 patients with IM (twelve boys and five girls) with mean age of 3.56¡À1.87 years (range 7 months to 7 years). Clinical diagnosis of IM was confirmed based on fever, lymphadenopathy, splenomegaly, lymphocytosis, atypical lymphocytes in blood smears and the elevated levels of IM antibody against EBV capsid antigen. The day of onset of fever was recognized as day 1 of illness. Blood samples taken during acute (3-5 days) and convalescent phase (10-15 days) were analyzed for expressions of CD19, CD19+/CD23+and CD23 on PBMC by Flow cytometry (FCM). The manifestation of fever and incidence of lower respiratory complications were recorded. Results: (1)The levels of CD19 and CD19+/CD23+ expressions were markedly decreased in acute stage(CD19 5.96¡À2.95%, CD19+/CD23+ 2.29¡À1.9%) and in convalescent stage(CD19 12.01¡À5.46%,CD19+/CD23+ 4.87¡À2.14%) in patients as compared with the healthy controls (CD1916.27¡À3.31%, CD19+/CD23+ 7.8¡À3.15%) (p<0.01). The earlier the history was, the lower the expressive levels were. (2)There was a positive correlation between the expressions of CD19 and CD19+/CD23+ during acute and convalescent stage (r=0.7163, 0.7652, p<0.01). (3) There was a negative correlation between the fever time and the level of CD19 in acute stage (r=0.8421, p<0.01)and the patients of lower CD19 had high incidence of lower respiratory complications . Conclusion: The results indicate that B cells especially CD23+ B cells were inhibited obviously during early stage in the patients with IM and the more evidently the CD19 decreased, the more serious the clinical symptoms was. The level of CD19 and CD19+/CD23+ expressions may be useful in diagnosis and forecasting the seriousness. The varied trend of CD23+,a mark of immortalized cells by EBV need to be observed longer. 1032