The Effects Of Antimicrobial Peptide On The Resistance To Bacterial Infection In Mice

Antimicrobial peptides,according to their multifunctional role in mammals,such as antimicrobial activity,promoting growth and immune regulation,have been a hot research topic in medicine,livestock farming and food industry.In this paper,the antibacterial peptides from the Brevibacillus laterosporus S62-9 play multiple roles in the mice immune defense,such as antibacterial infection and immune regulation.This experiment firstly studied the survival rate of the mice in antimicrobial peptides dose group（low dose group AMPs 20 AU/mL,middle dose group AMPs 40AU/mL,high dose group AMPs 60 AU/mL）and control group（AMPs 0 AU/mL）,according to the situation of the mice infected with the half lethal dose concentration of E.coli ATCC 25922 in 7 days.Data show that the survival rate of the control group 50%,high dose group 90%.The survival rate of the high dose group is significantly increasing.Then experiments studied the effects of antimicrobial peptides on the immune organs in mice,the number of inherent macrophages,the proportion of CD³⁺CD⁴⁺CD^8-/CD³⁺CD^4-CD⁸⁺cells and the concentration of cytokine TNF-a,the content of IL-10 in the mice blood:1)The index of the immune organs（spleen and thymus）was calculated in the antibacterial peptides dose group and the control group,through the anatomy of the mice.The results show that the control mice spleen index 2.34,middle dose group 3.19,high dose group 3.34.With increasing the concentration of the antimicrobial peptides,healthy mice spleen index in turn increased,and it found that the spleen index of the mice in the middle dose group and the high dose group increased significantly.2)The abdominal cavity fluid was collected from the mice in the high dose group and the control group,using the flow cytometry instrument to detect the resident mononuclear macrophages in healthy mice and the inflammation macrophages ratio after the bacterial infections in mice.The results demonstrate that the ratio of the resident mononuclear macrophages in the control mice 41.9%,high dose group 51.6%.AMP increases in the number of macrophages in mice.And,the ratio of inflammation macrophage in the control mice was 46.9%,28.8%in the high dose group.AMPs control effectively the number of the inflammation macrophages in mice.3)The percentage of CD³⁺CD⁴⁺CD^8-cells/CD³⁺CD^4-CD⁸⁺cells in mice blood was detected by using the flow cytometry instrument.The results show that the ratio of CD³⁺CD⁴⁺CD^8-cells/CD³⁺CD^4-CD⁸⁺cells in the control mice blood 2.73,high dose group3.65,and found that in the high dose group the ratio of CD³⁺CD⁴⁺CD^8-/CD³⁺CD^4-CD⁸⁺cells increased significantly.4)The mice serum was collected in the AMPs dose group and the control group,using ELISA kits to detect the content of TNF-a and IL-10.The results demonstrate that the concentration of TNF-a and IL-10 in the antibacterial peptides feeding mice,compared with the control group,increased slightly.5)The content of TNF-a and IL-10 in the blood of the mice injected with E.coli,was detected by using ELISA kits.Experimental data show that in the two groups of mice injected with a low dose of E.coli,the change trend of peripheral blood cytokines TNF-a and IL-10 is consistent.In two groups of mice injected with the lethal doses of E.coli,at the beginning of the bacterial infection,the antimicrobial peptides can make more effective inhibition of bacterial infection in mice but also raise the expression of IL-10and inhibit the secretion of TNF-a,join the inflammatory response to control inflammation and protect the body from damage.Depending on these experiments,results showed that the antibacterial peptides in mice immune function play a regulatory role.AMPs increase the number of macrophage in mice,at the same time,join in the mice inflammation reaction to curb inflammation and the increase of inflammation macrophages,control the secretion of pro-inflammatory factor TNF-a,promote the production of anti-inflammatory factor IL-10,inhibit excessive inflammatory reaction.