Effects of composite yeast culture on the expression of immune-related genes in the splenic tissue of weaned lambs.

The objective of this study was to evaluate the effects of dietary supplementation with a composite yeast culture (CYC) on the immune status and splenic gene expression in weaned lambs. Eighteen healthy, male weaned lambs of similar age and body weight were randomly assigned to three groups, including the control group (Con, basal TMR diet), the CYC1 group (TMR supplemented with 40 g/day/lamb of CYC), and CYC2 group (TMR supplemented with 50 g/day/lamb of CYC). The pre-feeding period lasted for 7 days, followed by a 40-day formal experimental period. Upon completion of the experiment, spleens were collected from the three groups of weaned lambs, weighed, and appropriate tissue samples were obtained for histological sectioning, ELISA analysis, RT-qPCR testing, and transcriptome sequencing. Hematoxylin-eosin (H.E.) staining results revealed that the area of splenic corpuscles in the CYC1 and CYC2 groups was significantly greater than that in the Con group (P < 0.05). Enzyme-linked immunosorbent assay (ELISA) analysis indicated that the levels of tuftsin, IgG, and IgM in the splenic tissues of the two experimental groups were significantly elevated compared to those in the Con group (P < 0.05). RT-qPCR results demonstrated that dietary supplementation with CYC1 or CYC2 significantly enhanced the mRNA expression of IL-2, IL-4, and IL-1β in the spleen tissue of weaned lambs (P < 0.05), while simultaneously suppressing the expression of IL-6 and TNF-α (P < 0.05). Transcriptomic analysis revealed that the differentially expressed genes (DEGs) in the splenic tissues of the CYC1 and CYC2 groups were predominantly enriched in pathways related to cell adhesion molecules and oxidative phosphorylation. Furthermore, weighted gene co-expression network analysis (WGCNA) revealed that the MEyellow and MEmagenta modules were significantly correlated with the expression levels of immune-related factors, including tuftsin, IgG, IgM, IL-2, and IL-4. Six potential candidate genes (ICAM1, CDH5, DQA, PTPRM, NDUFB8, and ATP5MC3) associated with these immune-related factors in the spleen were identified from these modules. Functional enrichment analysis indicated that ICAM1, CDH5, DQA, and PTPRM were enriched in the cell adhesion molecules signaling pathway, while NDUFB8 and ATP5MC3 were involved in the oxidative phosphorylation signaling pathway. In conclusion, supplementing the diet with CYC can enhance the histological development of the spleen in weaned lambs, increase the splenic contents of tuftsin, IgG and IgM, up-regulate the mRNA expression of IL-2, IL-4 and IL-1β, and down-regulate that of IL-6 and TNF-α, which may be achieved through cell adhesion molecules and oxidative phosphorylation signaling pathways. This study provides a theoretical foundation for further understanding of the regulatory mechanisms of splenic immune function by composite yeast culture in weaned lambs.