TLR7 trafficking and signaling in B cells is regulated by the MHCII-associated invariant chain

The evolving role of B cells in malignancies

B cells play diverse roles in different pathological circumstances, such as neoplastic diseases, autoimmune disorders, and neurological maladies. B cells, which are essential elements of the adaptive immune system, demonstrate exceptional functional variety, including the generation of antibodies, the presentation of antigens, and the secretion of cytokines. Within the field of oncology, B cells display a multifaceted nature in the tumor microenvironment, simultaneously manifesting both tumor-promoting and tumor-suppressing characteristics. Studies have found that the existence of tertiary lymphoid structures, which consist of B cells, is linked to better survival rates in different types of cancers. This article examines the involvement of B cells in different types of malignancies, emphasizing their importance in the development of the diseases and their potential as biomarkers. Additionally, the review also examines the crucial role of B cells in autoimmune illnesses and their potential as targets for therapy. The article also analyses the role of B cells in immunization and exploring their potential uses in cancer immunotherapy. This analysis highlights the intricate and occasionally contradictory roles of B cells, underlining the necessity for additional research to clarify their varied actions in various illness scenarios.

TLR7 Mediates HIV-1 Tat-Induced Cellular Senescence in Human Astrocytes

Cellular senescence contributes to accelerated aging, neuroinflammation, and the development of HIV-associated neurocognitive disorders (HAND) in the era of combined antiretroviral therapy (cART). One HIV viral factor that could lead to cellular senescence is the persistence of HIV-1 Tat in the brain. As a secreted viral protein, Tat is known to enter endolysosomes of cells through receptor-mediated endocytosis, and we have shown that Tat induces endolysosome damage and dysfunction. Significantly, endolysosome dysfunction has been strongly linked to cellular senescence. However, it is not known whether endolysosome dysfunction represents a driver or consequence of cellular senescence. Because Tat-induced endolysosome damage represents an early step in exogenous Tat-induced cellular senescence, we tested the hypothesis that Tat induces cellular senescence via an endolysosome-dependent mechanism in human astrocytes. We demonstrated that Tat interacts with an endolysosome-resident Toll-like receptor 7 (TLR7) via its arginine-rich basic domain, and such an interaction results in endolysosome damage and the development of a senescence-like phenotype including cell cycle arrest, enhanced SA-β-gal activity, and increased release of senescence-associated secretory phenotype (SASP) factors (IL-6, IL-8, and CCL2). Thus, our finding provided mechanistic insights whereby Tat induces endolysosome damage and cellular senescence in human astrocytes. We provide compelling evidence that endolysosome damage drives the development of cellular senescence. Our findings also highlight the novel role of TLR7 in the development of cellular senescence and suggest that TLR7 represents a novel therapeutic target against senescence and the development of HAND.

Activated B-Cells enhance epitope spreading to support successful cancer immunotherapy

Immune checkpoint therapies (ICT) have transformed the treatment of cancer over the past decade. However, many patients do not respond or suffer relapses. Successful immunotherapy requires epitope spreading, but the slow or inefficient induction of functional antitumoral immunity delays the benefit to patients or causes resistances. Therefore, understanding the key mechanisms that support epitope spreading is essential to improve immunotherapy. In this review, we highlight the major role played by B-cells in breaking immune tolerance by epitope spreading. Activated B-cells are key Antigen-Presenting Cells (APC) that diversify the T-cell response against self-antigens, such as ribonucleoproteins, in autoimmunity but also during successful cancer immunotherapy. This has important implications for the design of future cancer vaccines.

Single-cell profiling of CD11c+ B cells in atherosclerosis

Circulating CD11c+ B cells, a novel subset of activated B cells, have been linked to autoimmunity and shown to expand with age. Atherosclerosis is an age-associated disease that involves innate and adaptive immune responses to modified self-antigens. Yet, the expression of CD11c on specific B-cell subtypes and its link to atherosclerosis are poorly understood. In this study, we characterized the frequency of CD11c+ B cells in tissues in mice with aging. We observed an age-associated increase in CD11c+ B cells in the spleen and bone marrow of ApoE-/- mice, and this was associated with an increase in aortic plaque. In addition, we also utilized single-cell multi-omics profiling of 60 human subjects undergoing advanced imaging for coronary artery disease (CAD) to subtype CD11c+ B cells and determine their frequency in subjects with high and low severity of CAD. Using unsupervised clustering, we identified four distinct clusters of CD11c+ B cells, which include CD27 and IgD double negative 2 (DN2), age-associated (ABC), CD11c+ unswitched memory (USWM), and activated Naïve (aNav) B cells. We observed an increase in the frequency of both ABC B cells and DN2 B cells in patients with high CAD severity. Pathway analysis further demonstrated augmentation of autophagy, IFNg signaling, and TLR signaling in DN2 cells in high-severity CAD patients. On the other hand, an increase in the negative regulator of BCR signaling through CD72 was found in ABC cells in low-severity CAD patients. Through investigating scRNAseq of atheroma, these DN2 cells were also found to infiltrate human coronary atheroma.

TLR7 neo-functionalizes to sense dsRNA and trigger antiviral and antibacterial immunity in non-tetrapod vertebrates

TLR7 plays a crucial role in sensing viral ssRNA and initiating immune responses. Piscine TLR7 also responds to dsRNA challenge. dsRNA exists in almost all the viruses at specific stages. However, the mechanism on sensing dsRNA by TLR7 remains unknown. In the present study, we employed Ctenopharyngodon idella TLR7 (CiTLR7) to systematically explore the immune functions and mechanisms in teleost. CiTLR7 can directly bind not only ssRNA but also dsRNA at different patches in lysosome, recruit MyD88 as adaptor, and activate the downstream IFN pathway via SLC15A4/TASLa/TASLb/IRF5/IRF7 complex for antiviral and antibacterial infections and AP-1 pathway for pro-inflammatory cytokines. The key binding sites for dsRNA are L29 and L811 in CiTLR7. Further, we found that the function on recognizing dsRNA by TLR7 emerges in pisciformes and loses in tetrapods in evolution. This is the first report on sensing both ssRNA and dsRNA by a TLR member.

Toll-like receptors 7 and 9 regulate the proliferation and differentiation of B cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune illness marked by the loss of immune tolerance and the production of autoantibodies against nucleic acids and other nuclear antigens (Ags). B lymphocytes are important in the immunopathogenesis of SLE. Multiple receptors control abnormal B-cell activation in SLE patients, including intrinsic Toll-like receptors (TLRs), B-cell receptors (BCRs), and cytokine receptors. The role of TLRs, notably TLR7 and TLR9, in the pathophysiology of SLE has been extensively explored in recent years. When endogenous or exogenous nucleic acid ligands are recognized by BCRs and internalized into B cells, they bind TLR7 or TLR9 to activate related signalling pathways and thus govern the proliferation and differentiation of B cells. Surprisingly, TLR7 and TLR9 appear to play opposing roles in SLE B cells, and the interaction between them is still poorly understood. In addition, other cells can enhance TLR signalling in B cells of SLE patients by releasing cytokines that accelerate the differentiation of B cells into plasma cells. Therefore, the delineation of how TLR7 and TLR9 regulate the abnormal activation of B cells in SLE may aid the understanding of the mechanisms of SLE and provide directions for TLR-targeted therapies for SLE.

TLR7 Signaling in Lupus B Cells: New Insights into Synergizing Factors and Downstream Signals

PURPOSE OF THE REVIEW

Systemic lupus erythematosus (SLE) is driven by nucleic acid-containing antigens that stimulate endosomal TLRs. We review new advances in our understanding of how TLR7 signaling in B cells drives autoimmunity.

RECENT FINDINGS

Pathogenic B cell responses to TLR7 engagement are shaped by the disease-associated cytokine environment. TLR7, IFNγ, and IL-21 together promote the formation of autoreactive germinal centers and the ABC/DN2 B cell subset. BAFF and type 1 IFNs enhance autoantibody production from transitional B cells in concert with TLR7. TLR7 signaling components STAT1, BANK1, IRF5, SLC15A4, and CXorf21/TASL are associated genetically with SLE and important for lupus development in mice, while role of T-bet is controversial. Proper control of TLR7 trafficking by UNC93B1, syntenin-1, and αvβ3 integrin is critical for preventing autoimmunity. A better understanding of TLR7 signaling has revealed potential new therapeutic approaches for SLE, several of which are being tested in animal models or clinical trials.