Abstract:Objective: To study the lesion of mice thymus cells and the expression of Bax/Bcl-2 induced by Mycoplasma fermentans(Mf) and Mycoplasma pirum(Mpi).Methods: 47 ICR mice(clean class) were randomly divided into immunosuppressive group(n=35)and non-immunosuppressive group(n=12).The immunosuppressive model was made by intraperitoneal injection with cyclophosphamide(50mg/kg?d)every other day.The immunosuppressive group of mice were divided into Mf infected group、Mpi infected group and the normal saline (NS)control group. They were respectively received 0.3mL(6×108-9 /mL)Mf , Mpi and the sterile normal saline by intraperitoneal injection.The non-immunosuppressive group of normal mice were received equal amount of Mf by intraperitoneal injection.The mortality rates of each group were evaluated.The serum samples from each group of mice were taken for re-cultivation of the mycoplasma and the thymus tissue of the dead mice were subjected to ultrastructural observation by electron microscope.And the expression of Bax/Bcl-2 of mice thymus were analysed with immunohistochemistry.Results:The mortality rates of Mf and Mpi infected immunosuppressive group in comparison with the normal saline control group and Mf infected non-immunosuppressive group, which is statistical differences(P<0.05).The mycoplasma was positive in infected experimental group.Ultrastructural observation showed that the apoptosis of thymus cell in Mf and Mpi infected group were increased dramatically.It was found that significant enhanced existed in the expression of Bax/Bcl-2 of mice thymus between the infected group and the control group by immunohistochemistry(P<0.05).Conclusion:Mf and Mpi infections may induce the apoptosis of mice thymus cell,and promote the expression of Bax in the mice thymus.