[B cell subsets and the expression of CD40 in peripheral blood of patients with severe acute respiratory syndrome].

Objective: To explore the changing patterns of B cell subsets and the expression of CD40 on B cells in the course of severe acute respiratory syndrome (SARS) and their relationship to the severity of the disease.

Methods: Peripheral blood from 162 cases of SARS, 30 cases of mycoplasma pneumonia and 30 healthy adult volunteers were measured for the number of total B cells (CD19+ B cell), CD5 positive B cells (B1 cell) and mean fluorescent intensity of CD40 on B cell (CD40MF) using tri-color flow cytometry to analyze the distribution of the above parameters in SARS, mycoplasma pneumonia and healthy adult volunteers and their relation to the severity of SARS.

Results: The number of total B cells of clinically diagnosed SARS was (292 +/- 181) x 10(6)/L, significantly greater than that of healthy adults which was (200 +/- 65) x 10(6)/L (F = 6.17, P < 0.05) but smaller than that of patients infected with mycoplasma pneumonia which was (359 +/- 168) x 10(6)/L (F = 6.28, P < 0.05). During day 11 - 20 of the disease, the number of B1 cells of SARS patients was (24 +/- 14) x 10(6)/L smaller than that of healthy adults which was (39 +/- 20) x 10(6)/L (F = 4.23, P < 0.05). In the early stage of SARS (within 10 days), the expression of CD40 decreased significantly as compared with healthy adults (F = 5.13, P < 0.05). The number of B cells in severe SARS and mild cases were (347 +/- 156) x 10(6)/L and (268 +/- 211) x 10(6)/L respectively. The difference was statistically significant (F = 7.11, P < 0.01).

Conclusions: B cells, B1 cells and the expression of CD40 on B cells were involved in the pathogenesis of SARS. The B cell count correlated with the severity of SARS. The monitoring of B cells, B1 cells and the expression of CD40 on B cells is useful in the differential diagnosis of SARS.