Screening And Functional Study Of Lactobacillus With Immunomodulatory Activity

Lactobacillus is an important component of the body’s immune system,and it is an indispensable part of the body to maintain a stable state of immune function.It can improve the host’s immune activity through multi-mechanism regulation,thereby preventing and treating some diseases.With the development of my country’s dairy industry,probiotic research has developed rapidly in the food industry,and Lactobacillus is one of the largest probiotic strains.At present,there are few studies on the probiotic properties of Lactobacillus in dairy products in Hunan area.In this study,5 strains of lactobacillus strains isolated and preserved from the milk of the main mountain pastures in Hunan were selected as the research objects to evaluate the potential of probiotics and their immunomodulatory effects on macrophages in vitro.Lactobacillus with strong immunomodulatory ability;and to explore its immunomodulatory effect in vivo through an immunocompromised mouse model.The main findings are as follows:(1)The probiotic properties of 5 strains of Lactobacillus were investigated by p H and bile salt tolerance test,gastrointestinal fluid tolerance test,antibiotic sensitivity test,antibacterial activity test,adhesion Caco-2 cell test,and antioxidant activity test.The results showed that the five strains of Lactobacillus had certain resistance to environmental stress;they had certain inhibitory ability to Escherichia coli,Staphylococcus aureus and Listeria monocytogenes,and the diameters of the inhibition zones were all larger than 10 mm,20 mm and 13 mm,respectively;L.rhamnosus LZ260 has better probiotic properties,stronger adhesion,adhesion rate of 4.16%,DPPH free radical scavenging ability 56.36%,hydroxyl radical scavenging ability23.09%,total antioxidant capacity T-AOC content was 5.26 μmol/m L.(2)In vitro evaluation of 5 strains of Lactobacillus on macrophage RAW264.7 cell activity,phagocytic activity and immune activity molecules NO,cytokine tumor necrosis factor-α(TNF-α)and interleukin-10(IL-10)The effect of secretion level in order to screen out strains with good immunomodulatory effect.The results showed that L.rhamnosus LZ260 had a better immunomodulatory effect.At a specific concentration of Lactobacillus viable bacteria,it could significantly increase the cell activity,phagocytic activity and NO,TNF-α and IL-10 secretion level(p<0.05),the highest cell proliferation rate was 196.62%,the lowest lactate dehydrogenase(LDH)release was 554.36 U/100 m L;the highest phagocytic activity was 136.86%;the highest NO secretion was 5.70 μmol/ L;the highest IL-10 secretion was 15.56 pg/m L,and the highest TNF-α secretion was 50.98 pg/m L.(3)The immunocompromised mouse model was established by intraperitoneal injection of cyclophosphamide,and levamisole hydrochloride was used as a positive control to further verify the immune regulation effect of L.rhamnosus LZ260 suspension.The results show that L.rhamnosus LZ260 can exert immunomodulatory effects in many aspects,and has certain protective and repairing effects on the spleen of immunocompromised mice;it can improve the decrease in the number of blood cells in the state of bone marrow suppression;by increasing the serum Ig G(8.98 mg/m L),Ig M(1139.91 μg/m L)and Ig A(132.30 μg/m L)concentrations to enhance humoral immunity;increase Th1 secretion of IL-2(106.51 pg/m L)and IFN-γ(154.16 pg/m L),decreased Th2 secretion of IL-6(25.03 pg/m L)and IL-10(74.95 pg/m L),the results indicated that LZ260 of L.rhamnosus exerted an immunoregulatory function by regulating the imbalance of Th1/Th2.