Toll-like receptor 7 and 9 defects in common variable immunodeficiency.

Area of Science:

• Immunology
• Cell Biology
• Molecular Medicine

Background:

• Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinemia and impaired B cell function.
• Reduced numbers of isotype-switched memory B cells and plasma cells are hallmarks of CVID.
• Toll-like receptor (TLR) activation is crucial for initiating and sustaining normal B cell functions.

Purpose of the Study:

• To investigate the functional consequences of TLR7 and TLR9 signaling in B cells from patients with CVID.
• To assess the impact of TLR activation on B cell proliferation, isotype switching, and immunoglobulin production in CVID.
• To evaluate the role of interferon-alpha (IFN-alpha) in TLR-mediated B cell responses in CVID.

Main Methods:

• Examined TLR7, TLR7/8, and TLR9-mediated cell proliferation, isotype switch, and immunoglobulin production in control and CVID B cells.
• Quantitated cytokine production (TNF-alpha, IL-6, IL-12) in response to various TLR ligands.
• Measured IFN-alpha production by TLR7-stimulated peripheral blood mononuclear cells (PBMCs) and plasmacytoid dendritic cells (pDCs), and IFN-beta mRNA in fibroblasts.

Main Results:

• CVID B cells failed to proliferate, upregulate CD27, or shed surface IgD upon TLR7, TLR7/8, or TLR9 activation.
• TLR-stimulated CVID B cells did not upregulate activation-induced cytosine deaminase mRNA or produce IgG and IgA.
• TLR7-stimulated CVID PBMCs and pDCs produced minimal IFN-alpha; however, reconstituting IFN-alpha restored CVID B cell proliferation and isotype switching.

Conclusions:

• Defective TLR7 and TLR9 signaling in CVID B cells and pDCs, along with insufficient IFN-alpha production, significantly impairs CVID B cell functions.
• These TLR defects hinder the augmentation of humoral immunity mediated by TLRs in vivo in CVID patients.
• Targeting IFN-alpha pathways may offer a therapeutic strategy to restore B cell function in CVID.