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Objective To investigate the effect of albumin-bound paclitaxel (ab-PTX) on programmed death ligand 1（PD-L1) expression in lung squamous cell carcinoma H520 cells and its possible mechanism of action. Methods 1 Determination of ab-PTX concentration and duration of effect used in this study： H520 cells were cultured with 0. 001，0. 01，0. 1，1, and 10 μmol/L ab-PTX for 24，36, and 48 h. The cell proliferation inhibition rate was calculated, and finally, the 48 h with the most significant cell proliferation inhibition and its corresponding ab-PTX half maximal inhibitory concentration (IC50) value (1. 221 μmol/L) were selected for subsequent experiments. 2 Observation of PD-L1 expression in H520 cells after administration of different concentrations of ab-PTX in culture： lung squamous carcinoma H520 cells were cultured in vitro with 0，0. 001，0. 01，0. 1，1, and 10 μmol/L ab-PTX in culture medium for 48 h (based on the duration of ab-PTX action determined in 1）, and PD-L1 positive cell rate was measured by flow cytometry and PD-L1 mRNA was detected by qRT-PCR. 3 Observation of extracellular-regulated protein kinase (ERK) and p-ERK expression after administration of ab-PTX, ERK inhibitor alone or in combination in culture： the H520 cells were divided into the Control group, ab-PTX group, PD98059（ERK inhibitor) group, TPA (ERK activator) group, ab-PTX combined with PD98059 group, ab-PTX combined with TPA group; cells in the ab-PTX group were added with 1. 221 μmol/L ab-PTX (based on the ab-PTX concentration determined in 1）; in the PD98059 group，50 μmol/L PD98059 was added; in the TPA group, 50 nmol/L TPA was added; in the ab-PTX combined with PD98059 group，1. 221 μmol/L ab-PTX, and 50 μmol/L PD98059 were added; in the ab-PTX combined with TPA group，1. 221 μmol/L ab-PTX and 50 nmol/L TPA were added, and cells were cultured for 48 h. The PD-L1 positive cell rate was measured by flow cytometry, and ERK and p-ERK were detected by Western blotting. Results 1 PD-L1 expression in H520 cells after different concentrations of ab-PTX culture： The PD-L1 positive cell rates of H520 cell line cultured with 0，0. 001，0. 01，0. 1，1, and 10 μmol/L ab-PTX were 33. 9%±1. 1%，39. 5%±2. 7%，52. 6%±3. 3%，60. 3%±3. 4%，69. 9%±2. 3%, and 77. 8%±2. 2%, respectively, and the relative expression levels of PD-L1 mRNA were 1. 06±0. 07，1. 65±0. 22，2. 12±0. 16，3. 25±0. 11，3. 79±0. 14, and 4. 45±0. 28, respectively; with the increase of ab-PTX concentration, the PD-L1 positive cell rate and the PD-L1 mRNA relative expression gradually increased (all P<0. 05）. 2 Expression of ERK, p-ERK, and PD-L1 positive cell rate after the administration of ab-PTX, ERK inhibitor alone or in combination in culture： Compared with the Control group, the relative expression of p-ERK increased in the ab-PTX group, decreased in the PD98059 group and increased in the TPA group; the relative expression of p-ERK decreased in the ab-PTX combined with PD98059 group compared with the ab-PTX group and increased in the PD98059 group compared with the ab-PTX group; the relative expression of p-ERK was elevated in the abPTX combined with TPA group compared with the ab-PTX group and the TPA group (all P<0. 05). Compared with the Control group, PD-L1 positive cell rate increased in the ab-PTX group; compared with the ab-PTX group, the PD-L1 positive cell rate in the ab-PTX combined with PD98059 group decreased; compared with the PD98059 group, PD-L1 positive cell rate in the ab-PTX combined with PD98059 group increased; compared with the ab-PTX group and the TPA group, PD-L1 positive cell rate in the ab-PTX combined with TPA group increased (all P<0. 05). Conclusion Ab-PTX can upregulate PD-L1 expression in a dose-dependent manner within a certain range. The mechanism of action of ab-PTX up-regulating PD-L1 expression may be partly related to the activation of ERK signaling pathway. [ABSTRACT FROM AUTHOR]