Probiotics can affect multiple lymphocyte functions directly or indirectly. Animal models of antibiotic inhibition of intestinal probiotics have confirmed that Th1 cell function decreases in the absence of probiotics in the gut tube, while Th2 cell function increases and anti-infection immune function decreases. As the weather is getting hotter, the peak of various infectious diseases (especially intestinal infectious diseases) is coming. While reminding parents to pay attention to children’s personal hygiene, not to eat unclean food and not to go to crowded public places, they should also try to strengthen children’s own resistance to diseases, which is called “to protect the internal side before the external side”. Probiotics can enhance children’s immunity in many ways, providing a strong barrier to the invasion of infectious diseases. Building a balanced intestinal environment against pathogenic bacteria The intestinal tract is sterile before birth and the intestinal flora begins to colonize shortly after birth. Bifidobacteria are the dominant intestinal bacteria, followed by Lactobacillus, Bacteroidetes, and E. coli. Under normal condition, the composition and species of intestinal flora are stable, and they are closely combined with intestinal mucosa to form the biological barrier of intestine, which inhibits the overgrowth of conditional pathogenic bacteria and the invasion of foreign pathogenic bacteria through occupancy effect, nutritional competition and various metabolites and bacteriocins secreted by them, and maintains the micro-ecological balance of intestine. In addition, probiotics can enhance the barrier function of the epithelial cells of the gastrointestinal tract. Epithelial cells have receptors on their surface that recognize bacteria or viruses, the most important of which are Toll-like receptors (TLRs). Probiotic and pathogenic bacteria have different pathogen-associated molecular patterns (PAMPs) as ligands for TLRs. Pathogenic PAMPs stimulate epithelial TLRs and induce epithelial cells to produce inflammatory factors, causing intestinal inflammation. Probiotic PAMPs stimulate TLR2 and TLR4, induce the production of IL-6, stimulate Paneth cells to produce cryptosporin and defensin, inhibit the production of TNF-α induced by pathogenic bacteria PAMPs, thus promoting the proliferation and repair of epithelial cells, ensuring the integrity of barrier function and reducing local inflammatory response. Enhance immune function in multiple ways Probiotics can directly or indirectly affect a variety of lymphocyte functions. Animal models of intestinal probiotic inhibition by antibiotics confirm that Th1 cell function decreases in the absence of probiotics in the gut tube, while Th2 cell function is enhanced and anti-infection immune function is reduced. Lactobacillus and Bacillus divergens induce macrophages to express nitric oxide (NO) and inflammatory factors, enhance antiviral activity, and promote anti-infective immune responses. Other studies have shown that probiotics may enhance systemic immune function. In the study, the number of warm saline enemas and the incidence of diarrhea were lower in preterm infants given pefikon bulk (Bifidobacterium, Lactobacillus and Enterococcus faecalis) orally for 14 d than in the control group, and the levels of peripheral blood CD4+, CD4+/CD8+, IgM and IL-4 were higher than in the control group, suggesting that oral pefikon can stimulate T lymphocyte proliferation and differentiation, promote B cell secretion of immunoglobulins, upregulate CD45RO and memory T cell levels, and promote cytokine secretion. Prevention of food allergy Helper T cells are classified into Th1, Th2 and Treg (regulatory) depending on cytokine production. treg has both Th1 and Th2 immune response characteristics and plays an important role in immune tolerance to food or bacterial antigens by suppressing Th1 or Th2 overexpression through transforming growth factor (TGF-β). the balance of T cells and cytokine bypass plays an important role in regulating inflammatory response and immune tolerance. balance plays a role in regulating the inflammatory response and immune tolerance. These cytokines produced by activated T cells are both protective and involved in the inflammatory response to the host, and overexpression of these cell subtypes can also contribute to the development of allergy. Probiotics can reduce food allergy by inducing Treg production of the anti-inflammatory factor TGF-β, inhibiting T cell proliferation, reducing Thl and Th2 cytokine overexpression, balancing the T cell response, and correcting immune excursions.