Distinctions Among Circulating Antibody Secreting Cell Populations, Including B-1 Cells, in Human Adult Peripheral Blood1

Human antibody secreting cell (ASC) populations in circulation are not well studied. In addition to B-1 (CD20 + CD27 + CD38 lo/int CD43 + ) cell and the conventional plasmablast (CD20-CD27 hi CD38 hi ) cell populations, here we identified a novel B cell population termed 20 + 38 hi B cells (CD20 + CD27 hi CD38 hi ) that spontaneously secretes antibody. At steady state, 20 + 38 hi 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 + 38 hi B cells induces loss of CD20 and acquisition of CD138, suggesting that 20 + 38 hi B cells are precursors to plasmablasts, or pre-plasmablasts. We then evaluated similarities and differences between CD20 + CD27 + CD38 lo/int CD43 + B-1 cells, CD20 + CD27 hi CD38 hi 20 + 38 hi B cells, CD20 - CD27 hi CD38 hi plasmablasts, and CD20 + CD27 + CD38 lo/int CD43 - memory B cells. We found that B-1 cells differ from 20 + 38 hi 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 + 38 hi 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.