Objective    To investigate the effect of thymosin α1 (Tα1) on cellular immune function in gastric cancer patients through observing its treatment on the differentiation of T-lymphocyte subsets from screened peripheral blood mononuclear ce

lls (PBMCs).     Methods    PBMCs were obtained by centrifugation of blood samples from 18 healthy subjects and 32 patients with gastric cancer

and then cultured in the presence of culture medium with addition of Tα1 at 50

10 and 1 μg/ml for 2 d. T lymphocyte subsets (such as CD4

+

CD8

+

and CD4

+

CD25

+

Foxp3

+

T cells) and Th1/Th2 multiplex cytokines were detected by flow cytometry (FCM).     Results    After PBMCs isolated from healthy people and patients were incubated with or without Tα1

there was no significant change in percentage of CD4

+

CD8

+

peripheral lymphocyte subsets and ratio of CD4

+

/CD8

+

. There was no obvious change in the percentage of CD4

+

CD25

+

Foxp3

+

T lymphocyte subsets in the normal control

but a significant increase was observed in the cells from patients with gastric cancer after treatment (P0.05). Tα1 at 1 μg/ml induced the secretions of IL-1β and TNF-α in PBMCs from patients with respect to PBS treated cells

and 10 μg/ml of Tα1 increased the secretion of IL-6 in patient PBMCs. However

Tα1 had no such effect on multiplex cytokines in PBMCs from healthy people.     Conclusion    Tα1 increases the percentage of CD4

+

CD25

+

Foxp3

+

Treg cells in PBMCs from gastric cancer patients

and it may increase risk of patients for tumor immunotolerance.