Abstract: Objective   To study on the fluctuation of cytokines of T helper type 1（Th1） and T helper type 2 （Th2） after Toxoplasma gondii infection, as well as pathological damage of testis and apoptosis of spermatogenic cells in male rats.   Methods   Eighty-eight SD male rats (9-10 week old) were randomly and equally divided into normal control group and infection group. Rats in infection group were infected with 1×104 tachyzoites by intraperitoneal injection, while those in normal control group received same volume of PBS. On the day before infection and at the 3rd, 6th, 9th, 12th, ……, and 30th day post infection, four rats from each group were sacrificed for sera and testes. γ-interferon (IFN-γ) and interleukin-4 (IL-4) levels in sera were measured by ELISA. The testes were sliced and observed by microscope. The levels of apoptosis relative proteins Bcl-2 and Bax in seminiferous tubules were detected by immunohistochemistry. Results  IFN-γ in sera of infected rats increased rapidly with the peak ［(518.3±83.6) pg/ml］ at the 6th day post infection, and then decreased rapidly. IL-4 increased slowly with the peak ［(325.0±38.6) pg/ml］ at the 12th day, and then decreased. Both cytokines were significantly higher than the control (P<0.01) in the 30-day period. Pathological examination at the 6th day post infection showed that the cell levels of testicular seminiferous tubule disturbed. The number of primary and secondary spermatocytes decreased significantly. There were few sperms within the lumen or cavity which even closed. All the changes did not recover during 30 days. Bax expression in infected rats significantly increased in spermatogenic cells especially in spermatocytes at the 3rd day (P<0.05), reached a peak （0.547±0.037） at the 6th day, and then gradually decreased to normal after 15 days. The expression of Bcl-2 in infected rats did not change significantly (P>0.05).  Conclusion   T. gondii causes severe pathological damage in spermatogenic cells of the host. During the acute phase there appears Th1 cytokine polarization accompanied by high expression of apoptosis protein Bax, which is mainly expressed in spermatocytes. After rebalance of Th1/Th2, Bax protein expression decreases without noticeable recovery of spermatogenesis.

Key words: Toxoplasma gondii, Th1/Th2, Bcl-2/Bax, Spermatogenic cell