Innate Signaling Pathways in the Maintenance of Serological Memory: A Dissertation

Abstract

Long-term antiviral antibody responses provide protection from re-infection and recurrence of persistent viruses. Using a polyomavirus (PyV) mouse model, our lab has shown that MyD88-deficient mice generate low levels of virus-specific IgG after the acute phase of infection and that these IgG responses have a skewed isotype distribution with low levels of IgG2a/c. Moreover MyD88-deficient mice have reduced numbers of long-lived plasma cells in the bone marrow. These studies suggest an important role of MyD88-mediated signaling in long-term antiviral responses. Our lab has shown that T cell-deficient mice can also maintain long-term virus-specific IgG responses following PyV infection. The goal of this thesis is to evaluate the role of innate signaling pathways in maintaining serological memory to persistent virus infection and to elaborate on how long-term antiviral responses can be maintained in an immunocompetent or partially immune compromised, T cell-deficient host. Regarding T cell-dependent B cell responses, I set out to investigate the upstream and downstream components of the MyD88-mediated pathways required for normal antibody isotype and long-term humoral responses. IgG2a is a predominant immunoglobulin isotype in most virus infections. Wild type mice, in response to PyV infection, primarily induce antiviral IgG2a with some IgG1. MyD88-deficient mice in response to PyV infection display attenuated levels of virus-specific IgG2a, but normal levels of IgG1. Using Unc93B1 mutant mice (3d mice), which are defective in TLRs 3, 7 and 9 signaling, I show that 3d mice also generated low levels of virus-specific IgG2a following PyV infection. Studies in individual TLR3-/-, TLR7-/- or TLR9-/- mice displayed PyV-specific IgG2a responses similar to wild type responses. TLR7 and TLR9 double deficient mice generated similar skewed antibody isotype responses, where virus-specific IgG2a was reduced compared to wild type mice. This shows that TLR7 and TLR9-MyD88 mediated pathways are important in regulating IgG2a responses during a PyV infection. To investigate what components downstream of MyD88 are involved in mediating IgG2a responses, I worked with IRF5-deficient mice. IRF5 is a transcription factor that is activated upon stimulation of TLR7 or TLR9-MyD88-mediated pathways. Moreover, IRF5-deficient mice cannot generate autoantibodies specifically of the IgG2a isotype in a mouse lupus model, suggesting that IRF5 plays an important function in mediating class switching to IgG2a. In vitro studies where IRF5-/- B cells were stimulated with TLR7 or TLR9 ligands also generated low levels of γ2a germ-line transcripts, suggesting a B cell-intrinsic role for IRF5 in regulating γ2a germ-line transcription. PyV infection of IRF5-deficient mice resulted in similar skewed isotypes as observed in MyD88-deficient and 3d mice. To investigate a B cell-intrinsic role for IRF5 in regulating IgG2a responses in vivo upon PyV infection, I transferred IRF5-/- B cells and WT T cells into RAG KO mice prior to infection…