Recombinant Ehrlichia P29 protein, but not P13 protein, induces a protective immune response in a mouse model of ehrlichiosis (P4280)

Abstract

Abstract Ehrlichioses are emerging tick-borne bacterial diseases of humans and animals. The diseases are caused by obligately intracelluar bacteria belonging to the genus Ehrlichia. Currently, no vaccine is available against any ehrlichial diseases. Several immunoreactive proteins of ehrlichiae identified using immune sera from human patients and animals that include the major outer membrane proteins, ankyrin-repeat proteins and tandem repeat proteins (TRPs). In the present study, we evaluated E. muris P13 and P29 proteins, which are orthologs of E. chaffeensis TRP32 and TRP47, respectively, as subunit vaccines in a mouse model of ehrlichiosis. Immunization of mice with recombinant P29, but not P13, induced significant protection against a challenge infection. The protection induced by recombinant P29 was associated with the induction of a strong IgG antibody response. In contrast to development of IgG antibodies to P13 in all E. muris-infected mice, fewer animals infected with E. muris had IgG antibodies to P29. We hypothesize that polyclonal activation of B cells by CD4+ Th1 cells and subsequent development of hypergamaglobluinemia during persistent E. muris infection impairs formation of antibodies to antigens, such as P29, with low B cell precursor frequencies. In conclusion, our study indicated that Ehrlichia P29, but not P13, induces protective immune response, and induction of antigen-specific antibody responses impaired during persistent ehrlichial infections.