1.  Late endosomes and lysosomes (LELs) are organelles that control cellular homeostasis by degrading cellular cargo delivered by endocytosis, phagocytosis, and autophagy. We identified that diminished LEL acidification is evident in murine and human SLE, reducing the degradation of IgG-immune complexes (IgG-ICs). LELs that accumulate undegraded IgG-ICs undergo exocytosis, promoting the accumulation of nuclear self-antigen on the cell surface and increasing the levels of circulating immune complexes. Mechanistically, LEL dysfunction in lupus-prone MRL/lpr mice is induced by PI3k activation, in part coupled to Fcgamma receptor I (FcgRI). Deletion and/or inactivation of SHP-1 and SHIP-1 in non-autoimmune mice (C57BL/6) is sufficient to recapitulate the LEL dysfunction found in MRL/lpr mice. Further, deleting FcgRI in MRL/lpr mice is sufficient to attenuate B cell expansion, BAFF secretion, autoantibody production, and lupus. A cross-sectional study of LEL dysfunction in SLE patients, revealed that patients experiencing highly active disease showed nonacidic LELs, which were evident in a high proportion of patients with renal disease. In contrast, the LELs in patients experiencing inactive patients acidified much like healthy controls. Collectively, our findings strongly support a role for LEL dysfunction in murine and human SLE. Our current work focuses on murine proof-of-concept studies to define whether progression of SLE is attenuated when LEL acidification is restored.

 

2.  While B cell memory is an important aspect of humoral immunity, autoreactive memory cells play a role in perpetuating autoimmune response. Our studies of B cell memory during immune activation to foreign antigens and pathogens identified that BAFF secretion, elicited by productive antigen-antibody immune complexes, is a key cytokine that upregulates Bcl-6 expression in activated T and B cells. We hypothesized that the lack of long-lasting protection following Staphylococcus aureus (S. aureus) infection was disrupt because Protein A inhibited the binding of immune complexes to Fc gamma receptors, thereby diminishing BAFF secretion, Bcl-6, and productive T-B collaboration. Instead, we found that B memory responses were formed; however, S. aureus Protein A disrupted formation of long-lived plasma cells thereby decreasing S. aureus-specific antibody. This was associated with expanded short-lived extrafollicular B cell responses, limited proliferation of B cells in the bone marrow, and decreased longevity in bone marrow niches.

 

3.  My interest in tolerance extended to understanding how autoreactive B cells are regulated during innate immune responses. Although TLR4 activation was known as a polyclonal activator of B cell antibody responses, it remained unclear how autoreactive B cells maintain unresponsiveness during TLR4 stimulation, since TLR4 is expressed on autoreactive and naïve cells. We found that concomitant TLR4 stimulation of dendritic cells and macrophages induced the secretion of IL-6 and soluble CD40L, which selectively repressed Ig secretion by autoreactive B cells. Mechanistically, chronic BCR signaling in autoreactive B cells limited nuclear translocation of phospho-ERK, thereby maintaining an anergic phenotype. Thus, autoreactive B cells remain anergic during innate immune responses because receptor crosstalk between chronic BCR signaling and IL-6 receptor/CD40 signaling regulates TLR4-mediated Ig secretion.

 

4.  My early research focused on mechanisms of B cell tolerance involving the B cell antigen receptor (BCR). These studies identified a mechanism of BCR desensitization that resulted from dissociation of the Ig-alpha/Ig-beta signal transducing complex from mu-heavy chain of the BCR. Subsequent co-aggregation of receptors lacking Ig-alpha/Ig-beta with signal competent receptors attenuated BCR-mediated signaling. Mechanistically, we found that unsheathing of mu-heavy chain from Ig-alpha/Ig-beta was required for clathrin-mediated endocytosis and delivery of antigen to endosomes/lysosomes for antigen processing/presentation or degradation.

 

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For more information on current research, connect to the Vilen page on the UNC-CH Microbiology/Immunology.