| Fish mucosal surfaces are directly in contact with aquatic water that contains numerous pathogens.Thus,fish are easily vulnerable to various pathogens.Teleosts have evolved unique mucosa-associated lymphoid tissues(MALTs)that constitute the first line of defense against pathogens.The gill and nasal-associated lymphoid tissue(GIALT,NALT)are important components of the mucosal barrier in teleost fish.Teleost gills are important gas exchange tissues,and the GIALT plays a main role in protecting gill mucosal surface from pathogenic invasion during the air acquirement.In the respiratory tract of mammals,MALTs are the first physical barrier against viral pathogens,and secretory Ig A(s Ig A)is the main player in protecting respiratory tract mucosal by neutralizing viruses,or preventing viruses’adherence and invasion to epithelial cells.While,the function of different immunoglobulins(Igs)in teleost gill in immune defense against viral pathogens still needs further study.In this study,we analyzed the Igs and B cells responses of rainbow trout(Oncorhynchus mykiss)gills upon challenged with infectious hematopoietic necrosis virus(IHNV).Numerous of leukocyte hyperplasia in trout gills and the transcription level of anti-viral genes increased markedly when compared with controls.Moreover,local proliferation of Ig T~+B cells was detected,and significant Ig T-specific titers against the virus were generated in the gill mucus of the survived fish.More importantly,we demonstrated for the first time the function of gills s Ig T in viral neutralization.Our study suggesting the conservation of mucosal Ig in response to viral challenge of teleost fish and tetrapods.Many pathogens infect animal hosts via the nasal route.Teleost NALT has formed an effective immune barrier,while,teleost NALT s Ig responses to bacterial infection are still not well studied.In this study,rainbow trout was infected with Flavobacterium columnare via continuous immersion,after which the adaptive immune responses within NALT were evaluated.F.columnare could invade trout nasal mucosa and then cause histopathological changes in trout OO and induce the response of inflammatory gene.Moreover,the accumulation of Ig T~+B cells in trout nasal mucosa was induced by bacterial challenge,which was accompanied by strong bacteria-specific Ig T responses in the nasal mucus.These results suggested that trout nasal adaptive immune responses elicited by bacterial infection.Challenge experiments showed the highest survival rates in intranasal and intramuscular injection groups,while,immersion vaccination provides only transient protection.In mammals,the NALT is composed of organized lymphoid aggregates(O-NALT)and diffuse lymphoid tissue(D-NAL).Teleost NALT has been described as one D-NALT,whether there also exist O-NALT?Until recently,we noted the presence of a lymphoid structure that we have coined as organized NALT(O-NALT)in the olfactory organ of trout.This structure aggregates a large number of lymphocytes(i.e.,CD8α~+T,CD4-2b~+T,Ig M~+B and Ig T~+B cells).We found that the genes transcription level about T cells and Ig M~+B cells associated surface markers in O-NALT was significantly higher than those in D-NALT,which suggesting the different immune responses between O-NALT and D-NALT.The bacterial antigen uptake occurred via both O-NALT and D-NALT.Our results showed that the number of CD8α~+T and Ig M~+B cells in trout O-NALT significantly increased at 1 day post vaccination(dpv),while the number of Ig T~+B cells increased slightly but not significantly at 90 dpv.CCL19 can be as a biomarker for nasal vaccine responses in trout,and we also found the CCL19 increased notably both in O-NALT and D-NALT of rainbow trout at 1 dpv.Overall,our research for the first time identified the O-NALT in rainbow trout nasal,and explored its immune responses after intranasal vaccination.Our data provides new insights into the immune function of teleost NALT,which will help develop better vaccination strategies for salmonids via the nasal route. |
PDF Full Text Request