Isotype commitment of human B cells that are transformed by Epstein‐Barr virus

Abstract

Epstein-Barr virus (EBV) can transform a subpopulation of preactivated B cells thus promoting their growth and differentiation into plasma cells. In EBV-transformed clones of IgM-producing cells, the heavy chain constant region (CH) genes on the productive allele are fixed in germ-line configuration, whereas in isotype-switched clones the CH genes proximal to the expressed CH gene are deleted. In order to define more precisely the EBV-susceptible B cells, we sorted subpopulations of B cells on the basis of their cell surface Ig (sIg) isotypes, infected them with EBV, and determined which isotypes they could produce following transformation. Most precursors of IgM-producing plasma cells expressed both IgM and IgD on their surface, while a minority expressed IgM alone. Some B cell precursors of IgG- and IgA-producing cells also expressed sIgM, but surprisingly none expressed IgD. Those precursors of IgG and IgA producers, which bore sIgM, expressed it in relatively low levels, whereas B cells expressing high levels of sIgM were incapable of generating IgG and IgA producers. All of the precursors of IgG and IgA plasma cells expressed these isotypes on their cell surface. Interestingly, precursor B cells capable of producing the IgG3 and IgA2 subclasses could be respectively enriched on the basis of the presence or absence of cell sIgM. These results demonstrate the isotype precommitment of EBV-transformable B cells. They further suggest that residual IgM is transiently expressed on the surface of the IgG- and IgA-committed B cell precursors, whereas sIgD expression is extinguished earlier in the process of isotype switching via CH gene deletion.

Human immunoglobulin class and IgG subclass regulation: Dual action of interleukin‐4

“…Unlike most other human B cell mitogens, it is entirelyT cell independent, and it elicits secretion of all the Ig classes and IgG subclasses except for IgE [21,22,241 (Table 1). These properties of EBV have been exploited previously to show that IL-4 is required for IgE production by purified human B cells [4, 231. In this earlier work, B cells activated with EBVand cultured in v i m with 100 U/ml or more of IL-4 made IgE in the 10 to 100 ng/ml range.…”

“…Like LPS in the mouse, it is entirely T cell independent [21], and it elicits immunoglobulin secretion of all classes and subclasses [21,22]. EBV has been used previously to investigate isotype regulation in human B cells [4, 231, but the culture conditions employed and the timing of the response meant that B cell transformation rather than polyclonal activation may have been examined.…”

Anti-RhD-Mediated Immunosuppression: Can Monoclonal Antibodies Imitate the Action of Polyclonal Antibodies?

“…The Epstein-Barr virus, a B-lymphotropic human herpesvirus, infects B cells, including memory B cells, by using CD21 as a receptor and drives them out of the resting state to become activated proliferating lymphoblasts that produce and secrete Ig of any isotype (Miyawaki et al, 1988;Rickinson & Lane, 2000;Thorley-Lawson, 2001). The Epstein-Barr virus infection deregulates multiple differentiation factors and processes in B cells, promoting their growth and differentiation towards plasma cells (Miyawaki et al, 1991;Siemer et al, 2008). However, the process of differentiation fails to proceed to the terminal stage, to the plasma cell, thereby yielding cell lines with an immature "lymphoblastoid" phenotype; all virus-transformed cell lines that we obtained were CD19 +, CD20 +, CD38 +, Ig membrane +.…”

Switch recombination in normal IgA1+ Blymphocytes.

“…Relatively little is known about the biology of switched B cells or the molecular basis for their isotype switch because technical limitations imposed by their low frequency have thwarted this analysis. Commitment of isotype-switched human B cells to production and secretion of the isotype expressed on the surface has been observed in short-term cultures (29,30), and transfer of murine IgG2b B cells enriched by FACS can confer immunological class-specific memory (31). Several attempts to isolate switched B cells for molecular analysis have yielded evidence implying that switch recombination had not yet occurred in these cells.…”