Immune and gut microbiota regulation of live and heat-inactivated mixed Lactiplantibacillus plantarum and its postbiotics

Lactiplantibacillus plantarum (L. plantarum) and its postbiotics play significant roles in enhancing host immunity, protecting intestinal barrier function and maintaining gut microbiota homeostasis. This study investigated the effects of live L. plantarum and its postbiotics at varying doses on immune system, intestinal barrier integrity and gut microbiota modulation in immunosuppressed mice. Compared to the model control (MC) group, both live and heat-inactivated L. plantarum and its postbiotics significantly enhanced T lymphocyte proliferation and NK cell activity (P < 0.05). They also increased serum cytokine levels (TNF-α, IL-2, IL-4, IL-6, IL-10) and immunoglobulins (IgG and IgM) and upregulated mRNA expression of splenic cytokines (TNF-α, IL-2, IL-6, IL-10). Additionally, they elevated the mRNA expression levels of MyD88, p65, TLR4 and NF-κB in the spleen, thereby activated the TLR4/NF-κB immune signaling pathway. Meanwhile, all treatments significantly upregulated the mRNA expression of tight junction proteins (Claudin-1, Occludin-1 and ZO-1) and mucin (Muc-2), while increasing IgA+ plasma cell numbers in the jejunum (P < 0.05) compared with the MC group. Furthermore, at the phylum level, compared with the MC group, live L. plantarum mixed group (Mix group), low-concentration heat-inactivated L. plantarum mixed group (H-L-Mix group) and the high-concentration heat-inactivated L. plantarum mixed group (H-H-Mix group) all altered the composition of gut microbiota, characterizing by increased the abundance of Firmicutes and decreased the abundance of Proteobacteria. The postbiotic (PB) group showed a significant increase in the abundance of Verrucomicrobia and a decrease in the abundance of Proteobacteria. Compared with the MC group, all treatment groups significantly elevated the concentrations of acetic acid, propionic acid and butyric acid in the gut microbiota of mice (P < 0.05). These results suggested that postbiotics can become a new type of safe dietary supplement, replacing live Lactobacillus to regulate the body's immune activity.