Trypanosoma brucei brucei Infection Depletes Memory B Cells Resulting in Inability of the Host to Recall Protective B Cells Responses.

BACKGROUND Trypanosoma brucei brucei (T. b. brucei) evades host immune responses by multiple means, including the disruption of B cell homeostasis. This hampers anti-trypanosome vaccine development. As the cellular mechanism underlying this pathology has never been addressed, our study focuses on the fate of memory B cells (MBCs) in vaccinated mice upon trypanosome challenge. METHODS A trypanosome variant surface glycoprotein (VSG) and fluorescent phycoerythrin (PE) were used as immunization antigens. Functional and cellular characteristics of antigen-specific MBCs were studied after homologous and heterologous parasite challenge. RESULTS Immunization with AnTat 1.1 VSG triggers a specific antibody response and isotype-switched CD73 +CD273 +CD80 + MBCs, delivering 90% sterile protection against a homologous parasite challenge. As expected, AnTat 1.1 VSG immunization does not protect against infection with heterologous VSG-switched parasites. After successful curative drug treatment, mice were shown to have completely lost their previously induced protective immunity against the homologous parasites, coinciding with the loss of vaccine-induced MBCs. A PE immunization approach confirmed that trypanosome infections cause the general loss of antigen-specific splenic and bone marrow MBCs, and a reduction in antigen-specific IgGs. CONCLUSION Trypanosomosis induces general immunological memory loss. This benefits the parasites by reducing the stringency for antigenic variation requirements.