Objective To explore the mechanism of down-regulation of regulatory T cells (Treg) by immunization with attenuated activated autologous T cells. Methods Aulologous T cells were activated with ConA in vitro. Mice were immunized subcutaneously and inlraperitoneally every 5 days for 3 times (5 ×10~6 per time for each mouse), and the number and function of Treg were examined. PBS was subcutaneously injected for control group. Serum level of anti-mouse CD25 antibody was measured by ELISA. The number and function of Treg was detected by serum adoptive transfer and proliferation and inhibition assays. Results Compared with control group, there were less CD4~+ CD25~+ Foxp3~+ Treg in the mice after immunization (P < 0. 01), the immunosuppression ability decreased (P<0. 01), and the level of anti-CD25 antibody increased (P <0.01). Adoptive transfer of serum from immunized mice to naive mice led to a significant decrease in Treg population and function in recipient mice (P<0. 01). Conclusion Immunization with attenuated activated autologous T cells induces more anti-CD25 antibody, which may further down-regulate CD4~+CD25~+Foxp3~+ Treg expansion and function in vivo.

In the course of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infec-tion,to verify whether ursodeoxycholic acid(UDCA)can reduce angiotensin-converting enzyme 2(ACE2)receptor in BALB/c mice and reduce the risk of infection.UDCA was administered by in-tragastric administration to BALB/c mice for 7 d.During the treatment,the turbinate bones and lungs of mice were taken every day,and the changes of ACE2 content in the turbinate bones and lungs of mice were detected by ELISA.In addition,after 1,4 and 7 d of intragastric prophylaxis,BALB/c mice were infected with SARS-CoV-2 C57MA14 mouse adapted strain and SARS-CoV-2 Omicron DY1.1,respectively,after nasal inoculation,and viral load was detected on the turnings and lungs of mice 3 d after challenge to evaluate the preventive effect.In addition,UDCA was used to treat BALB/c mice infected with SARS-CoV-2 C57MA14 mouse adapted strain after nasal drops by gavage for 3 d,and the viral load of the mouse turbinate and lung was detected to evaluate the therapeutic effect.UDCA can decrease ACE2 content in turbinate and lung of BALB/c mice.How-ever,after 1,4 and 7 d of UDCA intragastric administration,there was no statistical difference in viral load in turbinate and lung of BALB/c mice between the prevention group and the virus con-trol group.There was no significant difference in the viral load of the turbinate and lung between the UDCA treatment group and the viral control group.UDCA could reduce the ACE2 content in the turnings and lungs of aged BALB/c mice,but the daily dose and duration of UDCA treatment had no significant effect on the mice infected with SARS-CoV-2 C57MA14 mouse adapted strain and SARS-CoV-2 Omicron DY1.1.