Abstract: Objective To determine whether morphine has the ability to enhance HIV-1 replication in MT-2 cells in vitro.Methods MT-2 cells were random assigned into morphine treatment group,morphine/naloxone co-treatment group,naloxone treatment group,and control group.The MT-2 cells in treatment groups were treated with morphine and/or naloxone for 24 hours,and then infected with HIV-1 strain.HIV-1 p24 antigen in MT2 cells culture supernatant collected at days 3,4,5 and 6 after the infection was determined.Results For the MT-2 cells infected with HIV-1 on the 3rd,4th,5th,and 6th day,the expressions of HIV-1 p24 antigen in 10-12 mol/L,10-10 mol/L and 10-8 mol/L concentration of morphine treatment group were increased significantly compared to those of the control(P< 0.01 for all).There was no significant difference in the expression of HIV-1 p24 antigen among morphine/naloxone co-treatment group,naloxone treatment group and control group(P > 0.05 for all).When MT-2 cells infected with HIV-1 on the 3rd,4th,5th,and 6th,the p24 antigen expressions were enhanced remarkably with significant difference among different concentration morphine treatment groups (P< 0.05).There were significant differences for different infection time in the p24 antigen expressions of three concentration of morphine treatment groups(P< 0.05),with an increase trend with the duration HIV-1 infection.Conclusion Morphine has the ability to enhance HIV-1 replication in MT-2 cell and the enhancement increases with the duration of HIV-1 infection.The morphine-mediated increase of HIV-1 p24 antigen expression could be blocked by the opiate receptor antagonist(naloxone).