Immune Response To HBsAg Can Not Be Enhanced With B7-H1Protein Vaccine

According to the report of World Health Organization, there are around2billion people who have been infected with hepatitis B virus (HBV). Amongthem, nearly350million are chronic HBV infectors. It is obvious that chronichepatitis B (CHB) has been one of the most serious diseases threatening humanhealth.The continuing replication of virus and the immune tolerance or lowimmune response in patients infected by HBV are two basic factors leading toCHB. Fortunately, more and more scientsts and clinicians have reached aconsensus: as long as upregulate and restore the anti-HBV immune response youcan conquer the chronic illness eventually. Therefore, it is still of great urgencyfor us to explore new therapeutic medicine and methods in recent tens years.In recent years, the study of programmed death1(PD-1) and programmeddeath1ligant1(PD-L1) have been the hot topics. Belonging to immunoglobuin super family, PD-1is one of type I transmembrane proteins and exists asmonomers. It can mediate negative regulatory signals and expresses on T and Blymphocyte. PD-L1, also known as B7-H1(B7homolog1), is the third memberof B7family, discovered by Dong et al. It is also one of type I transmembraneproteins and can express in antigen presenting cells (APC) and stellate cells.The PD-1/B7-H1signal path can negatively regulate the immune responsein which T and B cells participate. It can also be involved in immune toleranceprocess so that the immune function of virus specific cytotoxic T lymphocytescould be restrained. When there is virus infection, it can up-regulate theexpressions of PD-1and B7-H1. As a vital path for HVB to avoid immunologicalsurveillance and start the infection, the PD-1/B7-H1signal path could be aneffective therapeutic target of chronic HBV infection. It has been reported thatunder HBV immune tolerance status, HBV transgenic mouse (Tg mouse) yieldneither cellular nor humoral immune response. This feature is similar to thecircumstance of some chronic HBV infectors. Thus, HBV-Tg mouse can be usedas a model, in which B7-H1protein vaccine (manufactured by the department ofpharmacy，The Fourth Military Medical University), can be used to makeHBV-Tg mouse produce anti-B7-H1antibody and consequently, PD-1/B7-H1signal passway could be blocked, HVB immune response would be up-regulated,the chronic process of hepatitis B shall be weakened or even stopped, and HBVwill be finally eliminated. This in return provides the theoretical basis for a newCHB treatment method studied in this paper.The main contents and results of this paper are listed as follows:1. Immunize the HBV-Tg mouse with different dosages of hepatitis Bvaccine and B7-H1protein vaccine for four times altogether, respectively at the beginning of this experiment, the end of the second week, the fourth week andthe eighth week. And then the blood samples were taken at the rear of themouse’s orbit respectively in the first week, the third week, the fifth week, theseventh week, the ninth week, the eleventh week and the thirteenth week, andthe sera were isolated and stored at-20℃. The titer of B7-H1antibody in serumat different time points was tested by ELISA and there is no apparent differencebetween each group at the same time point.2. At the end of the fourteenth week, all of the immunized mouse weresacrifaced and their spleen cells were isolated for measurement of HBsAgspecificity secretion IFN-γT cell quantity, HBsAg specificity Th1type cytokines(IFN-γand IL-2) produced by mouse spleen cells and the lymphocyteproliferation. The results showed us that the amount of HBsAg specificity Th1type of cells secreting IFN-γ and IL-2secreted from the groups of miceimmunized with B7-H1(P＜0.05) were lower than the groups immunizedmerely with the same dosage of HBsAg protein immune. Nevertheless, there areno apparent differences in the amount of IFN-γ, the numbers of spleen cellssecreting IFN-γ and the lymphocyte proliferation abilities.The experiment has proved that B7-H1protein vaccine can induce theHBV-Tg mouse to generate obvious B7-H1antibody response, but cannotenhance the immune response to HBsAg. However, as showed by the test, asmall dosage of HBsAg can actually induce the HBV-Tg mouse to secrete Th1type cytokines (IFN-γand IL-2) and promote the proliferation of lymphocyte.Taken together, the experiment results tell us that anti-HBV immuneresponse can not be enhanced or upregulated only by blocking the PD-1-PD-L1passway, and it is possible and hopeful to breakdown the immune tolerance or restore the anti-HBV immune response after HBV infection by combineintervene pointing to multitargets and through more mechnism, and thereafterwe can realize or approach the ultimate goal, conquering and healing hepatitis Bthoroughly.