Abstract: Objective To investigate the relationship between apoptosis of peripheral blood lymphocytes (PBLCs) and impaired immunity by assessing the apoptosis and expression of Fas and Bcl-2 in PBLCs of patients with secondary syphilis. Methods Flow cytometry (FCM) was used to detect PBLC apoptosis as well as Fas and Bcl-2 expression in 33 patients with secondary syphilis and 30 normal controls. Results The Fas expression on PBLCs and CD4⁺ cells was significantly higher in patients than that in controls (P<0.01), which was contrary to the Bcl-2 expression. No significant difference was found in either Fas or Bcl-2 expression on CD8⁺ or CD19⁺ cells between patients and controls (P>0.05). The apoptosis levels were significantly higher in PBLCs and CD4⁺ cells in patients than those in controls (P<0.01), and were not different in the CD8⁺ or CD 19⁺ cells between patients and controls (P>0.05). In patients group, the apoptosis levels of both PBLCs and CD4⁺ cells had a positive correlation with the Fas expression (r=0.68, P<0.01;r=0.71, P<0.01, respectively), but a negative correlation with the Bcl-2 expression (r=-0.82, P<0.01;r=-0.74, P<0.01, respectively). Conclusions Dysfunction of cellular immunity may be due to the increased PBLC apoptosis in patients with secondary syphilis, which is associated with the abnormal expression of Fas and Bcl-2 on PBLCs.

Key words: Syphilis, Lymphocyte subsets, Apoptosis, Antigens, CD95, Proto-oncogene proteins c-bcl-2