OBJECTIVETo investigate immunomodulatory effect of Astragalus polysaccharides (APS) on IL-12-secreting dendritic cell (DC) subset CD11c(high)CD45RB(low) DC.

METHODSSpleen CD11c(high)CD45RB(low) DC and CD4(+)T lymphocytes in BALB/c mice were purified by magnetic beads sorting, and were treated with 0 (as control), 50, 100, 200 µg/mL APS. Immunofluorescence staining and flow cytometry were used to determine expressions of CD11c(high)CD45RB(low) DC surface molecules, including CD40, CD80, CD86, I-A/E, and Toll-like receptor (TLR) 4. IL-12 level in CD11c(high)CD45RB(low) DC culture supernatant was determined by ELISA. The CD4(+) T lymphocytes were divided into: normal control group, non-stimulation group (CD4(+)T lymphocytes cocultured with APS-unstimulated CD11c(high)CD45RB(low) DC), high-dose APS stimulation group (CD4(+)T lymphocytes cocultured with 200 µg/mL APS-stimulated CD11c(high)CD45RB(low) DC), high-dose APS stimulation+antibody 1 group (CD4(+)T lymphocytes cocultured with 200 µg/mL APS-stimulated CD11c(high)CD45RB(low) DC and IL-12 antibody), high-dose APS stimulation+ antibody 2 group (CD4(+)T lymphocytes cocultured with 200 µg/mL APS-stimulated CD11c(high)CD45RB(low) DC and IL-12 antibody isotype). Proliferation ability of CD4(+) T lymphocytes was determined with MTT method. IL-4 level as well as IFN-γ level in CD4(+)T lymphocyte culture supernatant was determined by flow cytometry. Data were processed with one-way analysis of variance.

RESULTSCompared with those in control, the expressions of CD11c(high)CD45RB(low) DC surface molecules (except for CD86) on CD11c(high)CD45RB(low) DC surface, as well as IL-12-secreting level with dose-dependence were increased in cells stimulated with 50, 100, 200 µg/mL APS. Proliferation ability of CD4(+)T lymphocytes in high-dose APS stimulation group was higher as compared with that in non-stimulation group (F = 13.438, P < 0.05). IFN-γ level in high-dose APS stimulation group \[(2784 ± 137) pg/mL\] was higher than that in non-stimulation group \[(1952 ± 101) pg/mL, F = 12.177, P < 0.05\]. IL-4 level in high-dose APS stimulation group was (172 ± 20) pg/mL, which was lower than that in non-stimulation group \[(193 ± 19) pg/mL, F = 11.963, P < 0.05\]. Proliferation ability of CD4(+) T lymphocytes, IFN-γ level, and IL-4 level in high-dose APS stimulation + antibody 1 group were all ameliorated when compared with those in non-stimulation group; while levels of the 3 indexes in high-dose APS stimulation + antibody 2 group were similar to those in high-dose APS stimulation group.

CONCLUSIONSAPS can activate IL-12-producing CD11c(high)CD45RB(low) DC, and further induce the activation of immune function of T lymphocyte with shifting of Th2 to Th1 in vitro. APS can enhance the immune response via promoting the phenotypic and functional maturation of CD11c(high)CD45RB(low) DC.