B cell expression of the SH2-containing inositol 5-phosphatase (SHIP-1) is required to establish anergy to high affinity, proteinacious autoantigens

• SHIP-1 is required for B cell anergy to hen egg lysozyme in the high affinity MD4.ML-5 immunoglobulin transgenic model.
• Low dose antigen exposure primes B cells for subsequent responses to antigen.
• SHIP-1 regulates responses of both naïve and antigen experienced B cells to antigen.
• SHIP-1 deficiency licenses naive MD4 B cells to both proliferate and differentiate upon transfer to antigen sufficient ML5.

Many self-reactive B cells exist in the periphery in a rapidly reversible state of unresponsiveness referred to as anergy. Reversibility of anergy indicates that chronically occupied BCR must transduce non-durable regulatory signals that maintain unresponsiveness. Consistent with such a mechanism, studies of immunoglobulin transgenic, as well as naturally occurring polyclonal autoreactive B cells demonstrate activation of the inositol 5-phosphatase SHIP-1 in anergic cells, and low affinity chromatin autoantigen-reactive B cells have been shown to require expression of this phosphatase to maintain anergy. However, it has been reported that anergy of B cells recognizing high affinity soluble antigen may not require SHIP-1, and is instead mediated by upregulation of the inositol 3-phosphatase PTEN. To further explore this apparent difference in mechanism we analyzed the effect of B cell-targeted SHIP-1 deletion on immune tolerance of high affinity anti-HEL B cells in mice expressing soluble HEL (MD4.ML-5). We report that SHIP-1 functions to dampen responses of naïve and low-dose antigen-primed B cells in vitro, and is required for induction of B cell tolerance. Thus, while anergy of B cells reactive with low affinity and likely polyvalent chromatin antigens is maintained by activation of inhibitory signaling circuitry involving SHIP-1, anergy of B cells recognizing soluble self antigen with high affinity also requires increased activity of SHIP-1.