The long-term objective of the proposed research is to determine how antibodies contribute to host defense against intracellular bacteria. Our model system uses the obligate intracellular bacterium Ehrlichia chaffeensis, the etiologic agent of human monocytic ehrlichiosis (HME). Preliminary studies have confirmed the feasibility of the mouse model to study immunity to E. chaffeensis, and its relevance to human disease. These studies have also revealed that significant immunity could be achieved in susceptible immunocompromised SCID mice after passive transfer of antibodies. Bacterial clearance was observed in some tissues even when antibodies were administered well after infection was established, and repeated antibody administration rescued mice from an otherwise fatal infection. Our preliminary studies have determined that Fc receptors for IgG are critical for antibody effectiveness, and that antibodies do not block bacterial adhesion or entry into cells. These later observations suggest that antibodies actively elicit critical effector functions in host phagocytes. The proposed studies will determine how antibody protects against intracellular infection, and will resolve the effector mechanism(s) involved.
The Specific Aims are to 1) Determine where antibodies encounter bacteria and mediate their effects in vivo, 2) Evaluate the role of particular FcgRs and antibody class during the humoral immune response, 3) Determine how inflammatory processes induced upon antibody administration contribute to host defense, and 4) Determine how antibodies, via FcgRs, affect the localization and survival of bacteria inside macrophages.
Aim#1 will resolve if the general mechanism of antibody mediated bacterial clearance by determining if antibodies mediate their effects only when bacteria are exposed during intercellular transfer.
Aim #2 will utilize several isotype switch variants of protective antibodies and gene targeted mice deficient for Fc receptors to identify which antibodies and receptors are critical for antibody efficacy.
Aim #3 will test the hypothesis that cytokines, complement, and other inflammatory mediators elicited upon antibody administration play important roles in host defense.
Aim #4 will utilize an in vitro infection model to determine if antibodies promote the fusion of phagosomes with lysosomes, and if antibodies can access bacteria in early endosomal compartments. Antibodies have previously been considered to be of little or no effectiveness during host defense against intracellular bacteria, so the study is significant not only for its relevance to our understanding of immunity to the ehrlichiae, but also because it will contribute to a re-evaluation of the tenet that antibodies are unimportant during intracellular bacterial infection, and a re-consideration of the value of antibodies for the treatment and prevention of diseases caused by these pathogens.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI047963-05
Application #
6984747
Study Section
Special Emphasis Panel (ZRG1-SSS-F (01))
Program Officer
Sawyer, Richard T
Project Start
2001-12-01
Project End
2007-11-30
Budget Start
2005-12-01
Budget End
2007-11-30
Support Year
5
Fiscal Year
2006
Total Cost
$238,071
Indirect Cost
Name
Wadsworth Center
Department
Type
DUNS #
153695478
City
Menands
State
NY
Country
United States
Zip Code
12204
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Munderloh, Ulrike G; Silverman, David J; MacNamara, Katherine C et al. (2009) Ixodes ovatus Ehrlichia exhibits unique ultrastructural characteristics in mammalian endothelial and tick-derived cells. Ann N Y Acad Sci 1166:112-9
Racine, Rachael; Chatterjee, Madhumouli; Winslow, Gary M (2008) CD11c expression identifies a population of extrafollicular antigen-specific splenic plasmablasts responsible for CD4 T-independent antibody responses during intracellular bacterial infection. J Immunol 181:1375-85
Reiley, William W; Calayag, Mark D; Wittmer, Susan T et al. (2008) ESAT-6-specific CD4 T cell responses to aerosol Mycobacterium tuberculosis infection are initiated in the mediastinal lymph nodes. Proc Natl Acad Sci U S A 105:10961-6
Bitsaktsis, Constantine; Winslow, Gary (2006) Fatal recall responses mediated by CD8 T cells during intracellular bacterial challenge infection. J Immunol 177:4644-51
Winslow, Gary M; Bitsaktsis, Constantine; Yager, Eric (2005) Susceptibility and resistance to monocytic ehrlichiosis in the mouse. Ann N Y Acad Sci 1063:395-402
Winslow, Gary M; Bitsaktsis, Constantine (2005) Immunity to the ehrlichiae: new tools and recent developments. Curr Opin Infect Dis 18:217-21
Yager, Eric; Bitsaktsis, Constantine; Nandi, Bisweswar et al. (2005) Essential role for humoral immunity during Ehrlichia infection in immunocompetent mice. Infect Immun 73:8009-16
Bitsaktsis, Constantine; Huntington, Jennifer; Winslow, Gary (2004) Production of IFN-gamma by CD4 T cells is essential for resolving ehrlichia infection. J Immunol 172:6894-901
Winslow, Gary M; Yager, Eric; Li, Julia Shu-Yi (2003) Mechanisms of humoral immunity during Ehrlichia chaffeensis infection. Ann N Y Acad Sci 990:435-43

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