The role of E3 ubiquitin ligase CBLB in mediating innate immunity to pulmonary infections

Sharma, Jaishree

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https://hdl.handle.net/2142/124497 Copy

Description

Title

The role of E3 ubiquitin ligase CBLB in mediating innate immunity to pulmonary infections

Author(s)

Sharma, Jaishree

Issue Date

2024-03-28

Director of Research (if dissertation) or Advisor (if thesis)

Nanjappa, Som G.

Doctoral Committee Chair(s)

Nanjappa, Som G.

Committee Member(s)

• Lau, Gee W.
• Witola, William H.
• Steelman, Andrew J.
• Nelson, Erik R.

Department of Study

Pathobiology

Discipline

VMS - Pathobiology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Innate immunity
• pulmonary infections
• fungal
• non-tuberculous mycobacterium
• CBLB
• lung

Abstract

Pulmonary infections are the leading infectious cause of hospitalizations and mortality in the United States. Pulmonary infections are common in immunocompromised patients due to the constant exposure and reduced resistance to pathogens. It is estimated that 2.7% of Americans, or around 8 million people, are immunocompromised due to HIV/AIDS, chemotherapy, and immunomodulatory medicines. Long-term use of antibiotics for other infections and prophylaxis, frequent hospital stays, corticosteroid use, and low CD4+ T cell counts enhance the risk of pathogens colonizing the airways of immunocompromised patients. When a pathogen reaches the alveoli, macrophages initiate an inflammatory response, which can either control the infection or overwhelm the host's already compromised immune system. Inflammatory processes in the lung parenchyma can impair gaseous exchange, leading to severe infections. The functions of the innate immune cells are controlled by many host factors early in infection. Deciphering the contribution and mechanisms of host factors implicated in different signaling pathways in immune regulation against pulmonary bacterial and fungal infections can help develop effective antimicrobial immunotherapies. Casitas B-lineage lymphoma proto-oncogene-b (CBLB), an E3 ubiquitin ligase, is one of the most important negative regulators of immune activation responsible for peripheral tolerance. CBLB is expressed in all leukocyte subsets that regulate signaling pathways in T cells, NK cells, B cells, and myeloid cells. In most cases, CBLB-deficient immune cells enhance T cell responses, and knockout or homozygous mutations in CBLB spontaneously develop autoimmunity and is associated with type 1 diabetes, Grave’s disease, and multiple sclerosis. Interestingly, genetic association studies link CBLB-polymorphisms with autoimmunity in humans. Additionally, the increased activation potential of CBLB-deficient cells renders them more potent to fight against malignancies or infections. While the role of CBLB in adaptive immunity has been extensively studied, the role of CBLB in myeloid cells during pulmonary fungal infections is not known. Here, we used Non-Tuberculous Mycobacteria (NTM) and pulmonary blastomycosis as mouse infection models to investigate the role of CBLB in innate immune cells during respiratory fungal infections. In Chapter 2, we address the gap in understanding the role of CBLB in modulating immune responses during pulmonary NTM infections under T-cell deficiency. NTM are ubiquitous environmental bacteria that may cause pathology ranging from chronic lung infections to fatal disseminated disease. The incidence and prevalence of NTM infections are increasing globally, partially due to increased immunocompromised patients. The diagnosis is often misleading, and the recent emergence of multi-drug resistant clinical strains has complicated the treatment of NTM disease. The first line of defense against lung infections is alveolar macrophages. However, in some instances, particularly in immunocompromised conditions, the potency of alveolar macrophages is reduced, which leads to increased lung pathology. CBLB is known to inhibit immune responses via proteasomal degradation of substrate proteins. However, the role of CBLB during Non-Tuberculous Mycobacterial infection is unknown, which encouraged us to define the role of CBLB in regulating innate immune responses following an NTM infection in an immunocompromised mouse model. We observed that loss of CBLB resulted in increased bacterial burden and dissemination following intravenous or intratracheal Mycobacterium avium infections under deficient T-cell responses in mice. At cellular levels, Cblb-deficiency impaired innate immune cells, including NK cells, inflammatory monocytes, and macrophages in vivo. However, Cblb-deficient macrophages were competent to control NTM growth and produced reactive oxygen species. Histopathology studies suggested that CBLB promotes the early formation of granulomas. Collectively, our study shows that CBLB is essential to mount productive innate immune responses and help prevent the dissemination of NTM during compromised T cell immunity. In Chapter 3, we aim to enhance our understanding of the role of CBLB in modulating immune response to fungal pathogens. Recently, even the World Health Organization (WHO) has advocated prioritizing fungal pathogens, highlighting the unavailability of any fungal vaccine and the urgent need to address this public health issue. Fungal pneumonia is life-threatening, especially in people with weakened immune systems or pre-existing lung disease. Fungal infections are becoming more common; however, there is no FDA-approved vaccine against fungal pathogens. Previous studies show that CBLB regulates antifungal immune responses during systemic candidiasis. However, the role of CBLB in myeloid cells during fungal pulmonary pneumonia is unknown. The immune response during fungal pneumonia involves the coordinated activation of myeloid and lymphoid cells to decrease fungal load and resolve lung pathology. Using a mouse model of blastomycosis, we observed that the ablation of CBLB only in myeloid cells enhanced fungal control and prolonged survivability of mice without exacerbating pathology. Mechanistically, at the cellular level, ablation of CBLB in myeloid cells enhanced the numbers and activation of alveolar macrophages and reduced the fungal burden. Myeloid cell-specific ablation of CBLB also increased ROS production from neutrophils, a known feature of fungal control. Depleting alveolar macrophages in myeloid cell-specific CBLB-ablated mice significantly increased the fungal burden. However, the immunity conferred was largely independent of  T cells. Depletion of Thy1.2+ cells increased the fungal burden, suggesting potential crosstalk of CBLB-ablated myeloid cells with lymphoid cells for boosting pulmonary fungal immunity. This dissertation contributes to understanding the immune mechanisms involved in host-microbe interactions during pulmonary infections. The findings highlight the potential of targeting CBLB in innate immune cells as an immunotherapeutic approach to combat pulmonary infections. By elucidating the role of CBLB in innate immune cells, this research provides valuable insights that can guide the development of novel preventive and therapeutic strategies for pulmonary infections, especially in immunocompromised patients.

Graduation Semester

2024-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2024 Jaishree Sharma

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