Overexpression of T-bet in HIV infection is associated with accumulation of B cells outside germinal centers and poor affinity maturation

Abstract

Nearly all chronic human infections are associated with alterations in the memory B cell (MBC) compartment, including a large expansion of CD19hiT-bethi MBC in the peripheral blood of HIV-infected individuals with chronic viremia. Despite their prevalence, it is unclear how these B cells arise and whether they contribute to the inefficiency of antibody-mediated immunity in chronic infectious diseases. We addressed these questions by characterizing T-bet–expressing B cells in lymph nodes (LN) and identifying a strong T-bet signature among HIV-specific MBC associated with poor immunologic outcome. Confocal microscopy and quantitative imaging revealed that T-bethi B cells in LN of HIV-infected chronically viremic individuals distinctly accumulated outside germinal centers (GC), which are critical for optimal antibody responses. In single-cell analyses, LN T-bethi B cells of HIV-infected individuals were almost exclusively found among CD19hi MBC and expressed reduced GC-homing receptors. Furthermore, HIV-specific B cells of infected individuals were enriched among LN CD19hiT-bethi MBC and displayed a distinct transcriptome, with features similar to CD19hiT-bethi MBC in blood and LN GC B cells (GCBC). LN CD19hiT-bethi MBC were also related to GCBC by B cell receptor (BCR)–based phylogenetic linkage but had lower BCR mutation frequencies and reduced HIV-neutralizing capacity, consistent with diminished participation in GC-mediated affinity selection. Thus, in the setting of chronic immune activation associated with HIV viremia, failure of HIV-specific B cells to enter or remain in GC may help explain the rarity of high-affinity protective antibodies.

Single cell resolution landscape of equine peripheral blood mononuclear cells reveals diverse immune cell subtypes including T-bet+B cells

“…In mice, T-bet + B cells have been shown to be important for antiviral humoral immunity (34,62,63). In humans, T-bet + B cells have been detected in peripheral blood in a variety of chronic inflammatory contexts including systemic lupus erythematosus (64,65), chronic malaria exposure (66,67), and chronic viral infection (16,40,68). Although a universal definition and designated function for these cells remains elusive, T-bet + B cells are often classified as atypical memory B cells and, at least in some contexts, are thought to arise from repetitive BCR stimulation (17).…”

“…Although a universal definition and designated function for these cells remains elusive, T-bet + B cells are often classified as atypical memory B cells and, at least in some contexts, are thought to arise from repetitive BCR stimulation (17). Indeed, human T-bet + B cells are enriched among virus-specific B cells in HIV infection (16). The equine T-bet + B cell populations identified in the present study share many features with the atypical memory B cell populations described in humans.…”

“…In addition to TBX21/T-bet expression, horse T-bet + B cell populations exhibit similar gene expression patterns, including enriched expression of FCRL4, FGR, and HCK, the protein products of which modulate BCR signaling (38). Furthermore, a recent study of T-bet + B cells in HIV demonstrated that they express genes characteristic of germinal center B cells (16). Interestingly, we detected specific expression of AICDA (encoding activationinduced cytidine deaminase) and elevated expression of APEX1 in equine T-bet + B cells, suggesting that the T-bet + B cells identified here may represent equine equivalents of the T-bet + atypical memory B cells described in humans.…”

“…Although specific markers and/or gene expression patterns vary in different datasets, these B cells are often found to express ITGAM (CD11b), ITGAX (CD11c), as well as genes that modulate BCR signaling (including FCRL4, FGR, and HCK) (35)(36)(37)(38)(39). Moreover, a recent study of T-bet + B cell populations in the context of chronic HIV infection demonstrated expression of genes associated with germinal center B cells (16,40). We assessed expression of several of these characteristic genes in B cell clusters, and observed patterns consistent with multiple reports in humans ( Fig.…”

“…Remarkably, we found that a large portion of the horse peripheral B cell compartment is comprised of T-bet + B cells. Cellular analogs of this population in human and mouse are associated with chronic infections (16,17).…”