Specificity-Based Negative Selection of Autoreactive B Cells during Memory Formation

Abstract

Autoreactive B cells are not completely purged from the primary B cell repertoire, and whether they can be prevented from maturation into memory B cells has been uncertain. We show here that a population of B cells that dominates primary immune responses of BALB/c mice to influenza virus A/PR/8/34 hemagglutinin (HA) are negatively selected in transgenic mice expressing PR8 HA as an abundant membrane-bound Ag (HACII mice). However, a separate population of B cells that contains precursors of memory B cells is activated by PR8 virus immunization and is subsequently negatively selected during the formation of the memory response. Negative selection of PR8 HA-specific B cells altered the specificity of the memory B cell response to a mutant virus containing a single amino acid substitution in a B cell epitope. Strikingly, this skewed reactivity resulted from an increase in the formation of memory B cells directed to non-self-epitopes on the mutant virus, which increased 8-fold in HACII mice relative to nontransgenic mice and precisely compensated for the absence of autoreactive PR8 HA-specific memory B cells. Negative selection of PR8 HA-specific B cells was a dominant process, since B cells from HACII mice could induce negative selection of PR8 HA-specific B cells from BALB/c mice. Lastly, HA-specific memory responses were unaffected by self-tolerance in another lineage of HA-transgenic mice (HA104 mice), indicating that the amount and/or cell type in which self-Ags are expressed can determine their ability to prevent autoreactive memory B cell formation.

Spontaneous Autoreactive Memory B Cell Formation Driven by a High Frequency of Autoreactive CD4+ T Cells

“…Interestingly, the subsequent fate of these autoreactive HA-specific B cells can differ dramatically in different HA Tg lineages; in HA104 mice (which express HA driven by an SV40 promoter/enhancer), memory responses to secondary virus immunization were comparable to those of BALB/c mice, indicating that PR8 HA-specific B cells could undergo memory formation despite overt autoreactivity (30). By contrast, PR8 HA-specific B cells were subjected to negative selection during memory formation in HACII mice, which express high levels of PR8 HA driven by an MHC class II promoter, including by B cells themselves (19). These studies indicated that specificity for a self-Ag can prevent autoreactive memory B cells that evade negative selection from the primary B cell repertoire from maturing into memory B cells, but that the ability to mediate this form of negative selection can be influenced by the amount and/or cell type in which a self-Ag is expressed.…”

“…PevHA, HACII, and TS1 mice have been previously described (19,31,32) and were backcrossed to BALB/c mice (Harlan Sprague Dawley) at least 10 generations before use in these experiments. All mice were maintained under specific pathogen-free conditions using sterile microisolators at The Wistar Institute Animal Facility.…”

“…We have been using transgenic mice expressing the influenza virus hemagglutinin (HA) 4 as a model self-Ag (HA transgenic (Tg) mice) to examine how autoreactive B cell responses are regulated at different stages of their development. Using virus immunization to induce the formation of HA-specific B cells, we have shown that a population of IgG-secreting B cells that dominates primary Ab responses to the PR8 HA in virus-immunized BALB/c mice is negatively selected due to its autoreactivity in HA Tg mice (19,29). However, a separate population of B cells that participates in both primary and memory responses of virus-immunized BALB/c mice persists in HA Tg mice, and can be activated to generate primary Ab responses by virus immunization (19,29).…”

“…Using virus immunization to induce the formation of HA-specific B cells, we have shown that a population of IgG-secreting B cells that dominates primary Ab responses to the PR8 HA in virus-immunized BALB/c mice is negatively selected due to its autoreactivity in HA Tg mice (19,29). However, a separate population of B cells that participates in both primary and memory responses of virus-immunized BALB/c mice persists in HA Tg mice, and can be activated to generate primary Ab responses by virus immunization (19,29). Interestingly, the subsequent fate of these autoreactive HA-specific B cells can differ dramatically in different HA Tg lineages; in HA104 mice (which express HA driven by an SV40 promoter/enhancer), memory responses to secondary virus immunization were comparable to those of BALB/c mice, indicating that PR8 HA-specific B cells could undergo memory formation despite overt autoreactivity (30).…”

“…However, this process is not complete and B cells expressing autoreactive specificities can be found in the peripheral B cell repertoire of healthy individuals (11)(12)(13)(14). B cells expressing autoreactive specificities can be actively regulated by anergy induction (15,16) or follicular exclusion (11,17,18) and can be negatively selected during memory formation by a dominant, B cell-intrinsic process (19). The induction of CD4 ϩ T cell tolerance to self-Ags can also be important in preventing autoantibody formation because autoreactive B cells can in some settings be driven to produce autoantibodies by provision of CD4 ϩ T cell help (20 -23).…”