Impact of BAFF Blockade on Inflammation, Germinal Center Reaction and Effector B-Cells During Acute SIV Infection

BAFFR activates PI3K/AKT signaling in human naive but not in switched memory B cells through direct interactions with B cell antigen receptors

Binding of BAFF to BAFFR activates in mature B cells PI3K/AKT signaling regulating protein synthesis, metabolic fitness, and survival. In humans, naive and memory B cells express the same levels of BAFFR, but only memory B cells seem to survive without BAFF. Here, we show that BAFF activates PI3K/AKT only in naive B cells and changes the expression of genes regulating migration, proliferation, growth, and survival. BAFF-induced PI3K/AKT activation requires direct interactions between BAFFR and the B cell antigen receptor (BCR) components CD79A and CD79B and is enhanced by the AKT coactivator TCL1A. Compared to memory B cells, naive B cells express more surface BCRs, which interact better with BAFFR than IgG or IgA, thus allowing stronger responses to BAFF. As ablation of BAFFR in naive and memory B cells causes cell death independent of BAFF-induced signaling, BAFFR seems to act also as an intrinsic factor for B cell survival.

The role of inflammatory mediators in the pathogenesis of periodic fever, aphthous stomatitis, pharyngitis and cervical adenitis (PFAPA) syndrome

INTRODUCTION

As a recurrent disease, periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) syndrome is characterized by episodes of febrile attacks and is often prominent in children under five years of age. However, the etiology of this condition has not been fully understood yet.

MATERIALS AND METHODS

The search in the extensive literature of peer-reviewed articles published from the inception to December 2021 was conducted to identify the relevant studies, using the electronic databases of MEDLINE/PubMed, Embase, Scopus, the Cochrane Library, and the Web of Science.

RESULTS

The analysis of complex relationships indicates that inflammatory factors, such as various cytokines and acute-phase proteins (APPs), play leading roles in the pathogenesis of this disease. Accordingly, this article summarizes the current state of knowledge to explain the mechanisms involved in inflammatory responses among patients with PFAPA syndrome and investigate its role in the pathogenesis of this disease. Moreover, the possibilities for further implementation of new therapeutic strategies are pointed out.

CONCLUSION

It is concluded that some pathophysiological processes are associated with immune dysregulation, which itself may be secondary to environmental factors, genetic background, and underlying diseases, including latent infections that multiply inflammatory mediators. elevated inflammatory markers similarly play a significant part in the clinical outcomes of this condition, whose pyrogenic nature is the reason for the development of episodes of febrile attacks in the population of patients suffering from PFAPA syndrome.

BAFF receptor polymorphisms and deficiency in humans

The BAFF-receptor (BAFFR) is a member of the TNF-receptor family. It is expressed only by B cells and binds BAFF as single ligand, which activates key signaling pathways regulating essential cellular functions, including survival, protein synthesis, and metabolic fitness. In humans, BAFFR deficiency interrupts B cell development at the transition from immature to mature B cells and causes B lymphopenia, hypogammaglobulinemia, and impaired humoral immune responses. Polymorphisms in TNFRSF13C gene affecting BAFFR oligomerization and signaling have been described in patients with immunodeficiency, autoimmunity and B cell lymphomas. Despite a uniform expression pattern of BAFFR in peripheral mature B cells, depletion of BAFF with neutralizing antibodies in patients with systemic lupus erythematosus does not affect the survival of switched memory B cells. These findings imply a distinct dependency of mature B cell subsets on BAFF/BAFFR interaction and highlight the contribution of BAFFR-derived signals in peripheral B cell development and homeostasis.

Evolution and Diversity of Immune Responses during Acute HIV Infection

Understanding the earliest immune responses following HIV infection is critical to inform future vaccines and therapeutics. Here, we review recent prospective human studies in at-risk populations that have provided insight into immune responses during acute infection, including additional relevant data from non-human primate (NHP) studies. We discuss the timing, nature, and function of the diverse immune responses induced, the onset of immune dysfunction, and the effects of early anti-retroviral therapy administration. Treatment at onset of viremia mitigates peripheral T and B cell dysfunction, limits seroconversion, and enhances cellular antiviral immunity despite persistence of infection in lymphoid tissues. We highlight pertinent areas for future investigation, and how application of high-throughput technologies, alongside targeted NHP studies, may elucidate immune response features to target in novel preventions and cures.

The Role of CXCL13 in Antibody Responses to HIV-1 Infection and Vaccination

CXCL13 signals through the G protein-coupled chemokine receptor CXCR5 to drive development of secondary lymphoid tissue as well as B cell and Tfh cell trafficking to germinal centers (GC), which leads to the differentiation of B cells to plasma cells and memory B cells. CXCL13 has been proposed as a general plasma biomarker for GC activities. In HIV-1 infected individuals, plasma CXCL13 levels have been associated with the rate of disease progression to AIDS. Moreover, CXCL13 production has been reported to be increased in HIV-1-infected lymph nodes, which may drive increased downregulation of CXCR5. In this review, we address the role of CXCL13 in HIV-1 infected individuals with regard to GC formation, generation of broadly neutralizing antibodies after infection and vaccination, and AIDS-related B cell lymphoma.

Distinct Features of Germinal Center Reactions in Macaques Infected by SIV or Vaccinated with a T-Dependent Model Antigen

B-cell follicles constitute large reservoirs of infectious HIV/SIV associated to follicular dendritic cells and infecting follicular helper (TFH) and regulatory (TFR) T-cells in germinal centers (GCs). Thus, follicular and GC B-cells are persistently exposed to viral antigens. Despite recent development of potent HIV immunogens, numerous questions are still open regarding GC reaction during early HIV/SIV infection. Here, we dissect the dynamics of B- and T-cells in GCs of macaques acutely infected by SIV (Group SIV+) or vaccinated with Tetanus Toxoid (Group TT), a T-dependent model antigen. Systemic inflammation and mobilization of antigen-presenting cells in inguinal lymph nodes and spleen are lower in Group TT than in Group SIV+. Despite spleen GC reaction of higher magnitude in Group SIV+, the development of protective immunity could be limited by abnormal helper functions of TFH massively polarized into TFH1-like cells, by inflammation-induced recruitment of fCD8 (either regulatory or cytotoxic) and by low numbers of TFR limiting TFH/TFR competition for high affinity B-cells. Increased GC B-cells apoptosis and accumulation of CD21lo memory B-cells, unable to further participate to GC reaction, likely contribute to eliminate SIV-specific B-cells and decrease antibody affinity maturation. Surprisingly, functional GCs and potent TT-specific antibodies develop despite low levels of CXCL13.