Objective To measure the quantities and apoptosis-related protein levels of B lymphocyte in the patients with immunorelated pancytopenia(IRP)and explore the action of B lymphocyte in the pathogenic mechanism of IRP. Methods Quantities of whole B lymphocytes and CD5+ B lymphocytes as well as the expressions of Fas and Bcl-2 in B lymphocytes in 35 patients with untreated IRP, 15 IRP patients in complete remission (CR), and 10 normal controls were assayed by flow cytometry. Results The percentages of B lymphocyte and CD5+ B lymphocyte were significantly higher in untreated IRP patients than in CR IRP patients and normal controls (P<0.05), and there was no significant difference between the latter two groups (P>0.05). There was no significant difference of Fas expression in B lymphocyte among three groups (P>0.05). The expression of Bcl-2 in B lymphocyte was significantly higher in untreated patients than in CR patients or normal controls (P<0.01), and significantly higher in CR patients than in normal controls (P<0.01). The apoptosis-related index was significantly lower in untreated patients than in CR patients or normal controls (P<0.05), and significantly lower in CR patients than in normal controls (P<0.05). The percentage of B lymphocyte was positively correlated with post-treated response time(r=0.53, P<0.01). Conclusion The production of auto-antibodies in IRP patients probably has some relationship with the abnormal quantities of B lymphocyte and its subpopulations as well as with the inhibition of B lymphocyte apoptosis. Objective To measure the quantities and apoptosis-related protein levels of B lymphocyte in the patients with immunorelated pancytopenia (IRP) and explore the action of B lymphocyte in the pathogenic mechanism of IRP. Methods Quantities of whole B lymphocytes and CD5 + B lymphocytes as well as the expressions of Fas and Bcl-2 in B lymphocytes in 35 patients with untreated IRP, 15 IRP patients in complete remission (CR), and 10 normal controls were assayed by flow cytometry. Results The percentages of B lymphocyte and CD5 + B lymphocyte were significantly There was no significant difference between the latter two groups (P> 0.05). There was no significant difference of Fas expression in B lymphocyte among three groups (P <0.05), higher than untreated IRP patients than in CR IRP patients and normal controls (P> 0.05). The expression of Bcl-2 in B lymphocyte was significantly higher in untreated patients than in CR patients or normal controls (P <0.01), and significantly higher in CR patients t The apoptosis-related index was significantly lower in untreated patients than in CR patients or normal controls (P <0.05), and significantly lower in CR patients than in normal controls (P <0.05). The percentage of B lymphocyte was positively correlated with post-treated response time (r = 0.53, P <0.01). Conclusion The production of auto-antibodies in IRP patients probably has some relationship with the abnormal quantities of B lymphocyte and its subpopulations as well as with the inhibition of B lymphocyte apoptosis.