OBJECTIVEEpstein-Barr virus (EBV) is a common causative agent of infectious mononucleosis (IM) and capable of efficiently immortalizing primary B cells into continuously growing lymphoblastoid cells in vitro. As B cell activation antigen, CD23 expression is induced by EBV infection of B cells and remains constitutively expressed at high levels in virtually all EBV-immortalized cells, which have been strongly linked to the development of B-cell lymphoproliferative disease and lymphoma. Whereas previous studies were performed in vivo in animals or ex vivo cultures, the present study aimed to explore the role of EBV-immortalized cells (CD23(+)/CD19(+)) in vivo analysis of children with EBV-IM.

METHODSIn a prospective trial, a group of 30 patients with IM (18 boys and 12 girls) with mean age of 3.9 +/- 1.3 years (range 6 months to 8 years) were enrolled. Clinical diagnosis of IM was confirmed based on fever, lymphadenopathy, splenomegaly, lymphocytosis (> 50%), atypical lymphocytes (> 10%) in blood smears and the elevated levels of IgM 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), early convalescent (about 11 - 15 days) and convalescent phase (about 30 - 45 days) were analyzed for expressions of CD19(+)/CD23(+), CD23, CD19 on peripheral blood mononuclear cells by flow cytometry (FCM) and was compared with those of control group.

RESULTS(1) The levels of CD23(+)/CD19(+) and CD23 expressions were markedly decreased in acute stage [CD23(+)/CD19(+) (2.22 +/- 1.47)%, (132 +/- 91)/mm(3); CD23 (3.12 +/- 1.88)%, (195 +/- 102)/mm(3)] and in early convalescent stage [CD23(+)/CD19(+) (4.51 +/- 2.25)%, (166 +/- 85)/mm(3); CD23 (5.55 +/- 2.76)%, (231 +/- 130)/mm(3)] in patients with IM as compared with those of the healthy controls [CD23(+)/CD19(+) (6.71 +/- 2.25)%, (215 +/- 68)/mm(3); CD23 (7.85 +/- 3.09)%, (249 +/- 86)/mm(3), respectively]. The earlier the history was, the lower the expressive levels were. The levels of CD23(+)/CD19(+) expressions returned to, but those of CD23 expressions exceeded, normal level in convalescent stage [CD23(+)/CD19(+) (6.72 +/- 2.16)%, (213 +/- 108)/mm(3); CD23 (9.46 +/- 2.73)%, (366 +/- 200)/mm(3)]. (2) There was a positive correlation in the expressions of CD23(+)/CD19(+) and CD23 among the three stages (P < 0.01). The positive correlation between the expressions of CD23(+)/CD19(+) and CD19 only occurred during acute stage (P < 0.01). There was no correlation between the expressions of CD23 and CD19 (P > 0.05).

CONCLUSIONEBV-immortalized cells and CD23(+) cells were inhibited effectively during the acute and early convalescent stage of IM. With the recovery of the disease, they gradually recovered and the levels of CD23 expressions exceeded normal level in convalescent stage.