Committed Human CD23-Negative Light-Zone Germinal Center B Cells Delineate Transcriptional Program Supporting Plasma Cell Differentiation

B cell affinity maturation occurs in the germinal center (GC). Light-zone (LZ) GC B cells (BGC-cells) interact with follicular dendritic cells (FDCs) and compete for the limited, sequential help from T follicular helper cells needed to escape from apoptosis and complete their differentiation. The highest-affinity LZ BGC-cells enter the cell cycle and differentiate into PCs, following a dramatic epigenetic reorganization that induces transcriptome changes in general and the expression of the PRDM1 gene in particular. Human PC precursors are characterized by the loss of IL-4/STAT6 signaling and the absence of CD23 expression. Here, we studied the fate of human LZ BGC-cells as a function of their CD23 expression. We first showed that CD23 expression was restricted to the GC LZ, where it was primarily expressed by FDCs; less than 10% of tonsil LZ BGC-cells were positive. Sorted LZ BGC-cells left in culture and stimulated upregulated CD23 expression but were unable to differentiate into PCs – in contrast to cells that did not upregulate CD23 expression. An in-depth analysis (including single-cell gene expression) showed that stimulated CD23-negative LZ BGC-cells differentiated into plasmablasts and time course of gene expression changes delineates the transcriptional program that sustains PC differentiation. In particular, we identified a B cell proliferation signature supported by a transient MYC gene expression. Overall, the CD23 marker might be of value in answering questions about the differentiation of normal BGC-cells and allowed us to propose an instructive LZ BGC-cells maturation and fate model.

CD23 Mediates Innate Immunity Against Aspergillus Fumigatus Infection in Human Alveolar Macrophages Through Activation by PU.1

Aspergillosis is a common cause of morbidity and mortality in immunocompromised populations. CD23 is a novel C-type lectin receptors (CLR) recognizing α-mannan and β-glucan in the cell wall of Aspergillus fumigatus (AF) that exerts a host innate immune response. However, the molecular mechanism underlying CD23 mediating immunity against AF infection in human alveolar macrophages is still unclear. In this study, we detected the expression of CD23 and PU.1 and the inflammatory markers IL-1β, IL-6, TNF-α and IL-10 by qRT–PCR, Western blotting and enzyme linked immunosorbent assay (ELISA) analysis in human alveolar macrophages (AMs) with AF infection. Phagocytosis of macrophages with altered CD23 expression and histological changes in lung tissues transfected with CD23-expressing adenoviruses in AF infection were investigated. Dual luciferase, chromatin immunoprecipitation assay (ChIP) and electrophoretic mobility shift assay (EMSA) was performed to detect the interaction of PU.1 and CD23. The results showed that the expression of CD23, PU.1 and these inflammatory markers increased significantly with the time of AF infection. Increasing CD23 expression strengthened the phagocytosis of AMs, and exogenous CD23 attenuated pathological defects in immunodeficient mouse lung tissues with AF infection. Moreover, CD23 was directly activated by PU.1. PU.1 siRNA resulted in downregulation of inflammatory marker expression, but overexpression of CD23 significantly increased the expression of these markers. Our study concluded that CD23 mediates innate immunity against AF in human AMs through activation of PU.1. Therefore, PU.1/CD23 may be a new anti-aspergillosis therapeutic for the treatment of invasive aspergillosis with the deepening of gene therapy and its wide application in the clinic.

Follicular lymphoma t(14;18)-negative is genetically a heterogeneous disease

Fifty-five cases of t(14;18)− follicular lymphoma (FL) were genetically characterized by targeted sequencing and copy number (CN) arrays. t(14;18)− FL predominated in women (M/F 1:2); patients often presented during early clinical stages (71%), and had excellent prognoses. Overall, t(14;18)− FL displayed CN alterations (CNAs) and gene mutations carried by conventional t(14;18)+ FL (cFL), but with different frequencies. The most frequently mutated gene was STAT6 (57%) followed by CREBBP (49%), TNFRSF14 (39%), and KMT2D (27%). t(14;18)− FL showed significantly more STAT6 mutations and lacked MYD88, NOTCH2, MEF2B, and MAP2K1 mutations compared with cFL, nodal marginal zone lymphoma (NMZL), and pediatric-type FL (PTFL). We identified 2 molecular clusters. Cluster A was characterized by TNFRSF14 mutations/1p36 alterations (96%) and frequent mutations in epigenetic regulators, with recurrent loss of 6q21-24 sharing many features with cFL. Cluster B showed few genetic alterations; however, a subgroup with STAT6 mutations concurrent with CREBBP mutations/16p alterations without TNFRSF14 and EZH2 mutations was noted (65%). These 2 molecular clusters did not distinguish cases by inguinal localization, growth pattern, or presence of STAT6 mutations. BCL6 rearrangements were demonstrated in 10 of 45 (22%) cases and did not cluster together. Cases with predominantly inguinal presentation (20 of 50; 40%) had a higher frequency of diffuse growth pattern, STAT6 mutations, CD23 expression, and a lower number of CNAs, in comparison with noninguinal cases (5.1 vs 9.1 alterations per case; P < .05). STAT6 mutations showed a positive correlation with CD23 expression (P < .001). In summary, t(14;18)− FL is genetically a heterogeneous disorder with features that differ from cFL, NMZL, and PTFL.