Fig 2: Vasoactive intestinal peptide (VIP) relieved lymphocytic infiltration in the submandibular glands (SMGs) of Sjögren's syndrome (SS) mice. (A) The water intake of the Control, SS model, and VIP groups were calculated on a weekly basis (n = 7). (B–G) SMG tissues were examined using hematoxylin-eosin (H&E) stained and observed under the 10x objective (B–D) and 20x objective (E–G). The lower left corner in (E–G) is a magnified panel for the black rectangle in the figure. (H) The Chisholm–Mason grade was determined. (I) Saliva flow rates were determined after receiving intervention for 8 weeks (n = 7). Scale bar: 200 µm. *p < 0.05, **p < 0.01, ***p < 0.001.

Fig 3: Vasoactive intestinal peptide (VIP) upregulated PTEN, VIP receptor mRNA expression, and Treg-related cytokines in spleen. Q-PCR results for VIP mRNA, VIP receptors mRNA expression (A), and PTEN/PI3K/AKT pathway (B) in the spleen. The concentrations of VIP in the serum (C) were measured using ELISA kits (n = 7). The abundance of interleukin (IL)-10 (D) and IL-2 (E) in the splenic tissue homogenate supernatant was determined by ELISA as well (n = 7). Unpaired Student t-test was used in the analysis. *p < 0.05, **p < 0.01, ***p < 0.001.

Fig 4: The effect of vasoactive intestinal peptide (VIP) on the phosphorylation of PTEN and PI3K/AKT in Splenic lymphocyte cells (SPLCs). (A) SPLCs were isolated from the nonobese diabetic (NOD) mice and plated for 12 or 24 h with different doses of VIP. A CCK-8 assay was used to detect the optical density (OD) value of each group. The data were analyzed by a mixed-effects model approach with Geisser-Greenhouse correction. Tukey's multiple comparisons post hoc test was conducted following analysis of variance (ANOVA). (B) SPLCs were transfected with 5 pM mpten931 (siRNA targeting PTEN). At 24 h post-transfection, the knockdown efficiency of mpten931 was determined by qRT-PCR. (C) Cells were treated with 125 ng/µL VIP for the indicated times at 24 h post-transfection. The data were analyzed with one-way ANOVA. (D) Representative WB experiments. Cells were transfected or not with mpten931 followed by treatment with 0 or 125 ng/µL VIP for 12 h. (E–G) Protein expression levels of total AKT, phosphorylated AKT, total PI3K, phosphorylated PI3K, and phosphorylated PTEN were analyzed by Western immunoblotting (WB). Cumulative data from three independent experiments. *p < 0.05, **p < 0.01.