Experimental Study Of Chinese Herbal Medicine Huangqi Maxingshigan Decoction In Treatment Of Avian Infectious Laryngotracheitis

This experiment was conducted to select the valid Chinese herbal medicine formulas and the best dosages for infectious laryngotracheitis (ILT) among the three different prescriptions modified from Maxingshigan Decoction, through studying the therapeutic effects on LTV chickens.Then, the possible working mechanism of the selected prescription was investigated.Methods:ILTV-Wanggang E4 strain was propagated, assayed and harvested on allantocherion from inoculated specified pathogen-free (SPF) chicken embryos.And it was passaged approximately four generations.Then,the EID50 was determined. 52-day-old chickens were inoculated intratracheally refer to 100EID50, and the clinical symptoms were observed.480 one-day-old chickens were randomly allocated into twelve groups of 40 birds each.Except for blank control group, other groups were infected with infectious laryngotracheitis virus via the intratracheal route on 52 d. Birds in drug treated groups were administrated with different concentration of every prescription respectively, as well as Ding Chuan San in groupⅩfor comparison at 36 h post-inoculation (54 d) when they showed clinical signs, 2 times daily for 5 days. Clinical observations and fatality were recorded. The effective power and cure rate of different prescriptions on ILTV chicken were calculated in order to screen the valid one.The possible working mechanism of the selected prescription named Huangqi Maxingshigan Decoction was investigated.160 one-day-old chickens were randomly allocated into four groups of 40 birds each.Except for blank control group, other groups were inoculated with infectious laryngotracheitis virus on 52 d, Birds in drug therapeutic groups were administrated with concentration of 0.4ml respectively, as well as Ding Chuan San in groupⅡfor comparison, 2 times daily for 5 days.10 chickens of every group were chosed randomly to take blood from the heart on day 5, 15, 25 postinfection, and serum for laboratory examination was collected, the SOD activity and MDA contents in serum was measured by spectrophotography.Then, the spleens were removed immediately and placed into liquid nitrogen. And then the expression levels of IFN-γand IL-4 mRNA, as well as the immunomodulation of Th1/Th2 imbalance in ILTV chicken spleen using semi-quantitative RT-PCR assay; the trachea was removed and fixed in bouin to detect the SIgA secreting cells.In addition, lung,liver, spleen,kkidney and bursa of fabricius were moved, and the dynamic distribution of ILTV in infected chickens at different time and different tissues was detected with the Polymerase Chain Reaction (PCR).Results:(1)ILTV infected model could be replicated succesfully, and it could be conformed by the clinical symptoms, the pathological appearances and PCR for ILTV.(2)The results of curing artificial infection ILT showed that, the total efficiency of prescriptionⅡwas 94.2%, the cure rate was 91.7%, it was confirmed that the therapeutic effect of prescriptionⅡon ILTV infection was significantly. (3) From 56 d postincubation, the SOD activity were elevated gradually. From 67 d to 77 d, the enzyme activities of SOD in drug treated groups were higher than other groups,and showed significance with blank control group (Ⅵ); the contents of MDA in serum decreased gradually,and showed significance with model group. (4)There exists the down-regulation of IFN-γand Th2-dominant Th1/Th2 imbalance when chickens were infected with ILTV 5 d postinfection. Then, IFN-γmRNA expression was elevated gradually, and the IL-4 mRNA expression decreased.Th2-dominant th1/th2 imbalance was changed. (5)The result indicated that the TK gene can be detected from the intratracheal route, lung, liver, bursa of fabricius and kidney 2 d postinfection. The tissues which was detected the highest efficiency were the intratracheal route and lung. (6)At 67 days, the areas of IgA secreting cells in groups challenged with virus continued to increase, but the the increasing format of groupⅡandⅢwere lower than Huangqi Maxingshigan Decoction Group. At 77 days, GroupⅠremain the increasing format, and showed significant difference with GroupⅡ,ⅢandⅣ( p<0.01). There exists significance between groupⅡandⅢ(p<0.05), and the blank control group remain the same;Conclusion: Huangqi Maxingshigan Decoction could enhance the SOD activity in serum of ILTV chickens, and lower the contents of MDA. Furthermore, Huangqi Maxingshigan decoction could extend the period of SOD in the body and improve the function of oxidative resistance. Huangqi Maxingshigan Decoction can significantly promote the expression level of IFN-γmRNA, and reduce the expression of IL-4 mRNA, induce the production of Th2 Dominant Immune Responses to enhance cellmediated immunity, ease inflammatory responses caused by ILTV.