Distinctions among Circulating Antibody-Secreting Cell Populations, Including B-1 Cells, in Human Adult Peripheral Blood

Abstract

Human antibody secreting cell (ASC) populations in circulation are not well studied. In addition to B-1 (CD20+CD27+CD38lo/intCD43+) cell and the conventional plasmablast (CD20-CD27hiCD38hi) cell populations, here we identified a novel B cell population termed 20+38hi B cells (CD20+CD27hiCD38hi) that spontaneously secretes antibody. At steady state, 20+38hi B cells are distinct from plasmablasts on the basis of CD20 expression, amount of antibody production, frequency of mutation, and diversity of B cell receptor repertoire. However, cytokine treatment of 20+38hi B cells induces loss of CD20 and acquisition of CD138, suggesting that 20+38hi B cells are precursors to plasmablasts, or pre-plasmablasts. We then evaluated similarities and differences between CD20+CD27+CD38lo/intCD43+ B-1 cells, CD20+CD27hiCD38hi 20+38hi B cells, CD20-CD27hiCD38hi plasmablasts, and CD20+CD27+CD38lo/intCD43- memory B cells. We found that B-1 cells differ from 20+38hi B cells and plasmablasts in numbers of ways, including antigen expression, morphological appearance, transcriptional profiling, antibody skewing, antibody repertoire, and secretory response to stimulation. In terms of gene expression, B-1 cells align more closely with memory B cells than with 20+38hi B cells or plasmablasts, but differ in that memory B cells do not express antibody secretion related genes. We found that, B-1 cell antibodies utilize Vh4-34, which is often associated with autoreactivity, 3 to 6-fold more often than other B cell populations. Along with selective production of IgM anti-PC, this data suggests that human B-1 cells might be preferentially selected for autoreactivity/natural-specificity. In sum, our results indicate that human healthy adult peripheral blood at steady state consists of 3 distinct ASC populations.

Autoantibody-producing plasmablasts after B cell depletion identified in muscle-specific kinase myasthenia gravis

“…Rituximab depletes CD20 + memory cells and, thus, indirectly diminishes the short-lived, mostly CD20 -plasmablast population (21,30), thereby affecting serological and clinical remission within a few months (5,6,31). One alternative version of this model acknowledges that a fraction of plasmablasts may be CD20 + (20); their direct depletion by rituximab could contribute to clinical response. Support for this model includes studies that point toward autoantibody production by plasmablasts in several autoimmune, rituximab-responsive disorders.…”

“…viable candidates. As only a small fraction of these cells express CD20, the effectiveness of rituximab in MuSK MG may depend upon depletion of a pool of plasmablast-progenitor CD20 + memory B cells (20,21). We recently had the opportunity to observe 3 previously rituximab-treated MuSK MG patients who were experiencing relapses after having achieved remission, indicating that the disease was not extinguished but dormant.…”

Human B-1 and B-2 B Cells Develop from Lin−CD34+CD38lo Stem Cells

“…Cells were stained and run in FACS buffer (2.5% FBS, 1 mM EDTA, 0.02% NaN 3 ). B cell subsets were gated as described in Quach et al 2016 (37), unless otherwise is noted.…”

“…Despite controversy (27–35), recently human B-1 cells are defined as (CD20 + CD27 + CD43 + CD38 lo/int ) with clinically relevant potential (36, 37). This population exhibits repertoire skewing toward expression of the immunoglobulin (Ig) VH4-34 gene (37), which encodes autoreactive antibody (38, 39), and produces natural antibodies (36), characteristics of mouse B-1 cells.…”

“…This population exhibits repertoire skewing toward expression of the immunoglobulin (Ig) VH4-34 gene (37), which encodes autoreactive antibody (38, 39), and produces natural antibodies (36), characteristics of mouse B-1 cells. In this study, we report that human Lin − CD34 + CD38 lo cells from cord blood, and bone marrow, give rise to both B-1 and B-2 cells; whereas, Lin − CD34 + CD38 hi cells do not give rise to B cells.…”