AUTHOR=Luo Tian , Patel Jignesh G. , Zhang Xiaofeng , McBride Jere W. 

TITLE=Antibody reactive immunomes of Ehrlichia chaffeensis and E. canis are diverse and defined by conformational antigenic determinants

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2024

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1321291

DOI=10.3389/fcimb.2023.1321291

ISSN=2235-2988

ABSTRACT=<p>For decades, the defined antibody reactive proteins of <italic>Ehrlichia chaffeensis</italic> and <italic>E. canis</italic> were limited to a small group with linear antibody epitopes. Recently, our laboratory has utilized an immunomics-based approach to rapidly screen and identify undefined <italic>Ehrlichia chaffeensis</italic> and <italic>E. canis</italic> antigenic proteins and antibody epitopes. In this study, we analyzed the remaining portion (~50%) of the <italic>E. chaffeensis</italic> and <italic>E. canis</italic> proteomes (<italic>n</italic> = 444 and <italic>n =</italic> 405 proteins, respectively), that were not examined in previous studies, to define the complete immunomes of these important pathogens. Almost half of the <italic>E. chaffeensis</italic> proteins screened (196/444) reacted with antibodies in convalescent HME patient sera, while only 43 <italic>E. canis</italic> proteins reacted with CME dog sera. New major immunoreactive proteins were identified in <italic>E. chaffeensis</italic> (<italic>n</italic> = 7) and <italic>E. canis</italic> (<italic>n</italic> = 1), increasing the total number of <italic>E. chaffeensis</italic> (n = 14) and <italic>E. canis</italic> proteins (n = 18) that exhibited antibody reactivity comparable to well-defined major antigenic proteins (TRP120 and TRP19). All of the <italic>E. chaffeensis</italic> but only some <italic>E. canis</italic> major immunoreactive proteins contained major conformation-dependent antibody epitopes. The <italic>E. chaffeensis</italic> immunoreactive proteins were generally small (&lt; 250 amino acids; ~27kDa) and the <italic>E. canis</italic> proteins were slightly larger (&gt; 320 amino acids; ~35 kDa). The majority of these new <italic>Ehrlichia</italic> major immunoreactive proteins were predicted to be type I secreted effectors, some of which contained transmembrane domains. Characterization of the immunomes of <italic>E. chaffeensis</italic> and <italic>E. canis</italic> and understanding the host specific <italic>Ehrlichia</italic> immune responses will facilitate identification of protective antigens and define the biophysical epitope characteristics vital to effective vaccine development for the ehrlichioses.</p>