Objective To investigate the effect of pulmonary microvascular endothelial cells (PMVECs) induced by interleron-γ (IFN-γ) on the proliferation of co-cultured T lymphocytes, and to explore its possible mechanism. Methods The lung tissues of female Balb/C mice were isolated, and mouse PMVECs were cultivated by tissue block method. After the identification of inverted microscope, transmission electron microscope observation and endothelial cell surface marker CD31 fluorescence detection identification, PMVECs with high purity were coufirmed. PMVECs were added to the lower chamber of the Transwell plate and then were randomly divided into five groups: the control group, 10 ng/mL group, 20 ng/mL group, 50 ng/mL group, and 80 ng/mL group, which were added with 0, 10, 20, 50, and 80 ng/mL IFN-γ, respectively. T-lymphocytes were added to the upper chamber of the transwell plate for co-culture, and flow cytometry was used to detect the T-lymphocyte proliferation index (PI) of the upper chamber. PMVECs of the third generation were randomly divided into two groups: the observation group and control group, which were added with 80 ng/mL IFN-γ and an equal amount of PBS, respectively; reverse-phase high-performance liquid chromatography was used to detect tryptophan, kynurenine and indoleamine 2, 3-dioxygenase (IDO) activity in the cell culture supernatant. The expression levels of IDO mRNA and protein were detected by RT-PCR and Western blotting, respectively. Results The T-lymphocyte PI of the control group, 10 ngl mL group, 20 ngmL group, 50 ngmL group, and 80 nglmL group were 3. 06 土0. 07, 2. 93 土 0. 09, 2. 46 士0. 28, 2. 21 士0. 41, and 2. 20 土0. 05, respectively; T-lymphocyte PI of the 20 nglmL group, 50 ng/mL group, and 80 ng/mL group was lower than that of control group (all P < 0. 01), but there was no significant difference in T lymphocyte Pl among 20 ng/mL group, 50 ngmL group, and 80 ng/mL group (all P > 0. 05). The observation group had a significantly lower tryptophan level in the cell culture supernatant than the control group, and the kynurenine level and !DO activity were higher than those of the control group (all P <0. 01). The relative expression levels of !DO mRNA in the observation group and the control group were 0. 68 土0. 02 and O, and the relative expression levels of !DO protein were 0.49 士0. 02 and O, respectively, with significant difference between every two groups (all P < 0. 01). Conclusion PMVECs treated with IFN-γ can inhibit the proliferation of co-cultured T lymphocytes by promoting tryptophan degradation, kynurenine accumulation, and !DO expression. [ABSTRACT FROM AUTHOR]