The origin and nature of age-associated B cells (ABCs) in mice are poorly understood. In this article, we show that their emergence required MHC class II and CD40/CD40L interactions. Young donor B cells were adoptively transferred into congenic recipients and allowed to remain for 1 mo in the absence of external Ag. B cells expressing the T-bet transcription factor, a marker for ABCs, were generated after multiple cell divisions from C57BL/6 donors but not from MHC class II– or CD40-deficient donors. Furthermore, old CD154 (CD40L)-deficient mice did not accrue ABCs, confirming that they arise primarily through T-dependent interactions. To determine what Igs ABCs express, we sequenced VH and Vκ rearranged genes from unimmunized 22-mo-old C57BL/6 mice and showed that they had a heterogeneous repertoire, which was comparable to that seen in old follicular and marginal zone B cell subsets. However, in contrast to the follicular and marginal zone cells, ABCs displayed significant somatic hypermutation. The mutation frequency was lower than found in germinal center cells after deliberate immunization, suggesting that ABCs have undergone mild stimulation from endogenous Ags over time. These observations show that quiescent ABCs are Ag-experienced cells that accumulate during T cell–dependent responses to diverse Ags during the life of an individual.
This work was supported by the Intramural Research Program of the National Institutes of Health, National Institute on Aging (to L.M.R.K. and P.J.G.) and by Grants PR130769 (Department of the Army) and R01 AG030227 (National Institute on Aging) (to M.P.C.). M.S.N. was supported in part by National Institute of Allergy and Infectious Diseases Grant T32 AI055428.
The online version of this article contains supplemental material.
Abbreviations used in this article:
- age-associated B cell
- activation-induced deaminase
- PE-labeled probe that recognizes HA of PR8
- marginal zone
- influenza strain A/Puerto Rico/8/1934.
- Received June 24, 2016.
- Accepted December 20, 2016.
- Copyright © 2017 by The American Association of Immunologists, Inc.