OBJECTIVEInfectious mononucleosis (IM) is a lymphoproliferative disease caused primarily by the Epstein-Barr virus (EBV) infection. The initial viral infection by EBV occurs in B lymphocytes and is followed by an extensive proliferation of T lymphocytes. Previous studies on immunity to EBV (including IM) have mainly focused on activation of peripheral blood T cells, which are responsible for the lymphocytosis in blood during acute IM. B cells, regarding CD23 as their activation marker, are the target cells of EBV infection. There are few reports on their effect in patients with IM. The role of them during acute IM is not known yet. The present study aimed to explore the action of B cells in patients with IM.

METHODSIn a prospective trial, a group of subjects comprised 22 patients with IM (14 boys and 8 girls) with mean age of 3.48 +/- 0.81 years (range 7 months to 8 years). 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) and convalescent phase (about 15 days) were analyzed for expressions of CD19, CD19(+)/CD23(+) on PBMC by flow cytometry (FCM) and was compared with those of control group. The number of the days with fever was recorded.

RESULTS(1) The levels of CD19 and CD19(+)/CD23(+) expressions were markedly decreased in acute stage [CD19 (5.63 +/- 2.91)%, (387 +/- 178)/mm(3), CD19(+)/CD23(+) (2.45 +/- 1.87)%, (160 +/- 99)/mm(3)] and in convalescent stage [CD19 (12.49 +/- 5.70)%, (428 +/- 156)/mm(3), CD19(+)/CD23(+) (5.05 +/- 2.79)%, (172 +/- 78)/mm(3)] in patients with IM as compared with those of the healthy controls [CD19 (16.20 +/- 2.80)%, (545 +/- 150)/mm(3); CD19(+)/CD23(+) (7.08 +/- 2.78)%, (249 +/- 136)/mm(3)]. The earlier the specimens were taken after onset, the lower the expressed levels were. (2) There was a positive correlation of the expressions of CD19 and CD19(+)/CD23(+) between acute and convalescent stage (P < 0.01);there was also a positive correlation between the expressions of CD19 and CD19(+)/CD23(+) during acute and convalescent stage (P < 0.01). (3) A negative correlation was found between the duration of fever and the level of CD19 and CD19(+)/CD23(+) in acute stage (P < 0.01).

CONCLUSIONThe results indicate that B cells and CD23(+) B cells were significantly inhibited during the onset of IM in the patients, that with the recovery of the disease, the condition was gradually improved, and that the more evidently the CD19 and CD19(+)/CD23(+) decreased, the more serious the clinical symptoms were and the longer time the recovery needed. The levels of CD19 and CD19(+)/CD23(+) expressions may be useful in diagnosis and predicting the severity.