Cross-immune Protection Induced By Staphyloc-occus Aureus GapC And Streptococcus Agalactiae GapC

Cow mastitis is an acute or chronic mammary gland inflammation caused by a variety of pathogens,which often causes serious economic losses.The common pathogens causing the mastitis are staphylococcus and streptococcus,and both of which have glyceraldehyde3-phosphate dehydrogenase C(GapC).GapC amino acid sequence is highly conservedis and can induce good immune response to and protection against staphylococcus or streptococcus.However,it is not clear whether staphylococcus GapC and Streptococcus GapC have cross-immunogenicity and induce cross-immune protection.In this study,we selected Staphylococcus aureus GapC and Streptococcus agalactiae GapC as the model of staphylococcus GapC or streptococcus GapC respectively,and analyzed the using bioinformatics methods,and investigated the GapC-induced cross humoral immune response,cellular immune response and survival rate of the immunized mice post challenge.Firstly,the physicochemical properties,immunogenicity,homology,common B and T cell epitopes of Staphylococcus aureus GapC and S.agalactiae GapC were analyzed and predicted by bioinformatics software.Then S.aureus GapC and S.agalactiae GapC were expressed and purified,and immunized to mice by intramuscular injection after emulsified with Fredrin’s adjuvant.On 7th day post the boost immunization,the cross immune response of CD4~+T cells and that of CD8~+T cells were detected.On 14th day post the boost immunization,the cross immune response and cross opsonophagocytosis of antibody to GapC were detected,and the bacterial load in the organs of and the survival rate of the immunized mice were observed after challenged with Staphylococcus aureus or S.agalactiae.Bioinformatics analysis showed that S.aureus GapC and S.agalactiae GapC had stable physical and chemical properties and good antigenicity.The homology of the two GapC was69.0%,and there were 5 common linear B cell epitopes,9 CD4~+T cell epitopes and 6 CD8~+T cell epitopes in both GapC,indicating that both GapC may have a certain cross-immunogenicity.The experimental results showed that,in terms of cellular immune response,both GapC induced significant proliferation of CD4~+T cells and secretion of IFN-γ,IL-17A and IL-4 by CD4~+T cells from the immunized mice,and significant cross response of proliferation and secretion of IFN-γand IL-17A by CD4~+T cells from the immunized mice.Both GapC also induced significantly proliferation of and secretion IFN-γby CD8~+T cells from the immunized mice,and cross response of proliferation of and secretion of IFN-γby CD8~+T cells significantly;in terms of humoral immune response,both GapC induced high levels of antibodies with opsonophagocyto-sis in the immunized mice,as well as significant antibody cross-reaction and antibody-mediated cross-opsonophagocytosis.After challenge with S.aureus HLJ23-1 strain,the survival rate of the mice immunized with S.aureus GapC was 80%,and that of the mice immunized with S.agalactiae GapC was 50%;after challenge with S.agalactiae LS0310 strain,the survival rate of the mice immunized with S.agalactiae GapC was 70%,and that of the mice immunized with S.aureus GapC was 80%.In conclusion,the results demonstrate that there is cross-immunogenicity between S.aureus GapC and S.agalactiae GapC,and they can induce significant cross-immune protection against S.aureus and S.agalactiae in mouse model.It provides important reference for further study of GapC being as a common antigen of vaccine candidate against S.aureus and S.agalactiae infections.