The landscape and function of anti-cytokine autoantibodies in health and immunodeficiency [electronic resource]
Keywords: Immunology.

A fundamental question in immunology is what accounts for the variability observed in susceptibility to infectious diseases. For the last 150 years, galvanized by Pasteur's germ theory of disease, microbiologists and immunologists have made great progress in advancing our understanding of the pathophysiology of infectious microbes. However, animal hosts with apparently identical exposures can have divergent courses of infection. This question can be appreciated by anyone who asks why one sibling falls ill with a common cold while the other does not. In the lay public, these differences are attributed to an individual having a "better immune system, " however in the scientific community we lack a significantly more sophisticated answer to this basic question. In this dissertation, I propose the hypothesis that anti-cytokine autoantibodies (ACAAs) are a factor contributing to the observed variation in susceptibility to infectious diseases. To test this hypothesis, I carried out three specific aims. First, new technologies were needed to address this question. In order to discover novel ACAAs, I developed and validated protein microarray technologies to screen for hundreds of ACAAs in hundreds of patient samples. Second, using protein microarrays and other tools, I performed deep profiling of ACAAs across multiple diseases. I screened blood samples from healthy controls and compared them to those from cohorts of patients with immunodeficiency phenotypes. I performed screens in more than a dozen different primary immunodeficiencies, including diseases with and without known causative genetic mutations and have included some of the most interesting results in this thesis. To summarize results from multiple experiments, a wide diversity of ACAAs are present in healthy individuals and patients with primary immunodeficiencies. In agreement with published findings from other laboratories, in a handful of primary immunodeficiencies, ACAAs against one or a few specific cytokines can be found at high titers and not in healthy controls. I add to this literature with the discovery of high-titer ACAAs against Type I interferon in RAG1/2 mutation-associated immunodeficiency. For some other immunodeficiencies, specific ACAAs can be found at, on average, higher levels than in healthy controls, but these ranges of reactivity still overlap with reactivities found in healthy controls. For example, our discovery of IFN- ACAAs in Immunodysregulation Polyendocrinopathy Enteropathy X-Linked (IPEX) adds to this literature. Third, association with disease does not prove causation. In order to gather evidence for a causal role of ACAAs in contributing to immune deficiency, I purified and tested the function of ACAAs in vitro for blocking activity. I found that some ACAAs, like those against IFN- in IPEX, block in vitro, while others like those found in Wiskott Aldrich Syndrome do not. Taken together, these studies demonstrate that, in health and disease, the human immune system generates a diverse antibody response that reacts against a wide spectrum of antigens, including cytokines. ACAAs, in a few rare diseases, are capable of causing disease with full penetrance. However, our studies provide preliminary evidence that ACAAs may exert partially penetrant phenotypes, including phenotypes potentially based on combinations of ACAAs. Future studies, including immunoglobulin passive transfer studies, will be useful in assessing the contributions of ACAAs to infectious and non-infectious phenotypes.