Author ORCID Identifier

https://orcid.org/0000-0002-5065-3961

Date of Award

Summer 6-12-2023

Document Type

Thesis (Ph.D.)

Department or Program

Microbiology and Immunology

First Advisor

Margaret E. Ackerman

Abstract

Understanding antibody responses across various immunological conditions can provide valuable insights for the advancement of therapeutic as well as prophylactic interventions. IgG subclass responses, in particular, have garnered the most attention because of their potential role in disease outcomes and treatment efficacy. The four IgG subclasses differ in their hinge region and “constant region” and these differences in turn modulate their antibody functions. Some subclasses demonstrate robust antibody effector functions, while others exhibit diminished effector functions. The consequences of these differences can either be advantageous or disadvantageous, contingent upon the specific context in which they occur.

This thesis explores the nature of these IgG subclasses in two immunological conditions: Kidney transplant rejection and HIV/AIDS. First, using Human Leukocyte antigen (HLA)-A2-specific IgGs as a model, we applied systems serology tools to investigate qualitative features of IgG alloantibodies including subclass, receptor binding properties, and glycosylation profiles. The microscale purification method allowed us to purify HLA-A2 specific antibodies from patient sera and evaluate Fc glycosylation profiles of different IgG subclasses. We observed that the levels of afucosylated anti-A2 IgG1s were elevated in seropositive patients suggesting potential cytotoxicity via FcγRIII-mediated mechanisms. Using glycoengineered monoclonal and naturally glycovariant polyclonal HLA-A2 specific IgG, we were able to establish that afucosylated DSA may be a biomarker of AMR and contribute to pathogenesis. Next, we characterized the effector functions of such HLA-A2 specific IgGs. When comparing antibody features in individuals who had AMR versus individuals who didn’t have AMR, we observed higher ADCP and ADCC activity in individuals who had AMR. This suggests the possible role of these antibody effector functions in mediating graft rejection. We also observed that the HLA-A2 specific IgG responses were influenced by different factors such as recipient sex, CDC crossmatch status and sensitization event. In the later part, we explore on the IgG subclass responses in HIV infection and vaccine trials, highlighting the benefits of more potent IgG1/3s responses. Finally, we developed a platform to investigate the impact of IgG subclass on BCR stimulation. Understanding the IgG responses in different settings will thus help in developing targeted interventions for specific immunological conditions.

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