We previously reported that RO ؉ expression correlated with increased mutation, activation, and selection among human germinal center (GC) B cells. Here, we subdivided human tonsillar B cells, including IgD ؊ CD38 ؉ GC B cells, into different fractions based on RB expression. Although each subset contained RB ؉ cells, when used as an intrasubset marker, differential RB expression effectively discriminated between phenotypically distinct cells. For example, RB ؉ GC B cells were enriched for activated cells with lower AID expression. RB inversely correlated with mutation frequency, demonstrating a key difference between RB-and RO-expressing GC B cells. Reduced RB expression during the transition from pre-GC (IgM ؉ IgD ؉ CD38 ؉ CD27 ؊ ) to GCB cells was followed by a dramatic increase during the GC-to-plasmablast (IgD ؊ CD38 ؉؉ CD27 ؉ ) and memory (IgD ؊ CD38 ؊ CD27 ؉ ) transition. Interestingly, RB ؉ GC B cells showed increased signs of terminal differentiation toward CD27 ؉ post-GC early plasmablast (increased CD38 and RO) or early memory
IntroductionImmune function is uncompromisingly governed by at least 3 interdependent principles including recognition, effector function, and transition. Early naive B and T cells that successfully bind foreign antigen become activated and undergo developmental transition toward more mature, faster responding memory subsets. In contrast, lymphocytes that bind self-antigen in the periphery are usually counterselected against and undergo a different type of transition, one toward apoptosis or anergy. Ineffectual negative selection against self-specific B cells has been associated with the development of autoimmune and neoplastic diseases. Unfortunately, potential factors responsible for the redirection or abrogation of transitions toward cell death and anergy have not been conclusively determined. Antibody sequence analyses revealed that B cells participating in autoreactive responses are often mutated and show signs of selection for self-antigen. 1,2 This suggests that somatic hypermutation (SHM) during proliferation and activationbased transitions in the dynamic germinal center reaction may play a role (whether direct or indirect) in disease pathogenesis.We therefore sought to develop an expedient approach that would allow for the reproducible identification of B-cell populations that exist at different transitional stages based on their states of activation, SHM-dependent diversification, and developmental progression toward adjacent downstream subsets. Delineating how surface marker profiles change as B cells transition between key stages (especially when immunoregulatory markers such as CD45 protein tyrosine phosphatase are included in such profiles) should increase our understanding of B-cell development and ultimately how to circumvent dysregulated processes that could lead to disease.Over the past 3 decades, our research laboratory has investigated multiple aspects of human B-cell development and the molecular processes that collectively shape the peripheral BCR repertoi...