Kinetics Andmolecular Mechanismof Memory B Celldevelopmentin Mice Immunized With Plague Vaccines

Plague is a zoonotic disease caused by the Gram-negative bacterium Yersiniapestis, which is usually transmitted to humans from infected rodents via the bite of aninfected flea. Historically, plague was a lethal infectious disease that afflicted humanpopulations.Plague has been recently classified as a re-emerging disease by the WorldHealth Organization and has attracted considerable attention because of its potentialmisuse as an agent of biological warfare or bioterrorism.To prevent this disease, bothlive attenuated vaccines (LAV) and killed whole-cell vaccines (KCV) against plaguehave been used in humans since the early part of the20thcentury. However, KCVonly provide short-term protection against bubonic plague.The LAV EV76iseffective against bubonic and pneumonic plagues, but it has side effects of varyingseverity and has not been used in the Western world at present. The DNA and subunitvaccines based on Y. pestis F1and LcrV antigens alone or in combination wereefficacious against both bubonic and pneumonic plagues,and had obvious advantagesover traditional vaccinesin terms of efficacy or safety, and are beingdevelopedcurrently.In our previous work, to develop a safe and effective plague subunit vaccine,highly purified natural F1antigen from Y. pestis EV76was extracted using a newpurification strategy and a non-taggedrV270proteincontaining amino acids1to270of LcrV was prepared using thrombin digestion from recombinant Escherichia coliBL21cells. The subunit vaccine, which comprises a dose20μg F1and10μg rV270that wereadsorbed to25%(v/v) alhydrogel in PBS buffer (SV1), provides goodprotective efficacy against Y. pestis challenge in mice, guinea pigs, rabbitsand rhesusmacaques.In addition, long-termprotection and antibody response forLAV EV76andthe subunit vaccine F1+rV270were determined in mouse model.The completeprotection against lethal challenge of Y. pestiscould be achievedup to day518afterprimary immunization. Antibodies to F1and rV270were still detectable over a periodof518days. These results indicate that the immunity elicited by plague vaccines islong-lived. Interestingly, after challenging with Y. pestison day56,126or518, nosignificant anti-F1antibody titre boost was observed in the group SV1or the groupEV76within21days. This result seems not to be consistent with the conclusion thatthe memory B cells could quickly produce more antibodies when they are exposed tothe same antigen. Long-lived plasma cells and memory B cells are responsible for the long-termhumoral immunity elicited by vaccination.The serum antibody levelis maintained bylong-livedplasma cells. Memory B cells are in charge of drivingthe rapid anamnesticantibody response that occurs after re-exposureto antigen.Memory Bcells also play arole in replenishing the pool of long-livedplasma cells to maintain long-term antibodylevels in the absence ofpathogen.Therefore, we suppose that memory B cells elicitedby plague vaccines are short-lived in vivo, and that long-term humoral immunity maybe maintained by long-term plasma cells.RNA-Seq determination showed15765difference genes between memory Bcells and na ve B cells,including697up-regulated genes,820down-regulatedgenesand131genes associated with immune responses. There are16304differencegenes between plasma cells and na ve B cells, including1574up-regulated genes,451down-regulated genes and162genes associated with immune responses; There are16212difference genes between memory B cells and plasma cells, including1495up-regulated genes,252down-regulated genes and164genes associated with immuneresponses.Many up-or down-regulated genes associated with complement receptor,immunoglobulin, lymphocyte antigens and cytokines were observed in na ve B cells,memory B cells and plasma cell, among which the profile of up-or down-regulatedgeneswas different.