Date of Award

4-29-2021

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ping Wang, MD

Second Advisor

Monowar Aziz, PhD

Abstract

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Cold-inducible RNA-binding protein (CIRP) is a 172 amino acid nuclear protein that, once released into the extracellular environment, has been found to act as a damage-associated molecular pattern (DAMP) and contribute to the inflammatory reaction in states of sepsis and hemorrhagic shock. B-1 cells are a subset of B lymphocytes with unique innate and adaptive immune properties. B-1a cells are responsible for approximately 80% of serum IgM in the circulation of a non-immunologically challenged host. B-1a cells can also act as antigen-presenting cells and secrete regulatory cytokines such as interleukin (IL)-10 and granulocyte-macrophage colony-stimulating factor (GM-CSF). The adoptive transfer of B-1a cells into septic mice has been shown to provide survival benefits and ameliorate end-organ damage in sepsis. Sialic acid-binding immunoglobulin-type lectin-G (Siglec-G) is a membrane-bound protein highly expressed on B-1 cells. Siglec-G functions to inhibit B cell receptor (BCR) activation of B cells by recruiting the tyrosine phosphatase Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP-1) and blocking calcium signaling. We hypothesized that extracellular CIRP (eCIRP) downregulates Siglec-G expression on B-1a cells, shifting them to a proinflammatory phenotype, contributing to the sepsis inflammatory cascade. WT and CIRP-/-mice were subjected to cecal ligation and  puncture (CLP) to simulate intraabdominal sepsis. Peritoneal cavity (PerC) B-1a cells were decreased in septic mice, but their numbers were preserved in CIRP-/- mice. Siglec-G expression was also found to be dramatically reduced on B-1a cells in WT septic mice but preserved in CIRP-/- mice. Intra-peritoneal (i.p.) injection of recombinant murine CIRP was able to mimic this response seen in septic WT mice. B-1a cells treated with Siglec-G blocking antibodies were found to produce greater quantities of proinflammatory cytokines in response to eCIRP stimulation compared to B-1a cells treated with IgG control. WT mice were subjected to mesenteric ischemia-reperfusion injuries and treated with B-1a cells at the time of reperfusion. B-1a cell-treated mice showed reduced end-organ damage, dampened immune responses, and higher IgM titers. These studies suggest eCIRP plays a crucial role in altering the function of B-1a cells in states of immunologic challenge, and targeting eCIRP’s effect on B-1a cells and Siglec-G expression could be a novel therapeutic avenue for the treatment of surgical emergencies.

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