Bruton’s Tyrosine Kinase Promotes Persistence of Mature Anti-Insulin B Cells

Abstract

Autoreactive B lymphocytes are essential for the development of T cell–mediated type 1 diabetes (T1D). Cytoplasmic Bruton’s tyrosine kinase (BTK) is a key component of B cell signaling, and its deletion in T1D-prone NOD mice significantly reduces diabetes. However, the role of BTK in the survival and function of autoreactive B cells is not clear. To evaluate the contributions of BTK, we used mice in which B cells express an anti-insulin BCR (125Tg) and promote T1D, despite being anergic. Crossing Btk deficiency onto 125Tg mice reveals that, in contrast to immature B cells, mature anti-insulin B cells are exquisitely dependent upon BTK, because their numbers are reduced by 95%. BTK kinase domain inhibition reproduces this effect in mature anti-insulin B cells, with less impact at transitional stages. The increased dependence of anti-insulin B cells on BTK became particularly evident in an Igκ locus site–directed model, in which 50% of B cells edit their BCRs to noninsulin specificities; Btk deficiency preferentially depletes insulin binders from the follicular and marginal zone B cell subsets. The persistent few Btk-deficient anti-insulin B cells remain competent to internalize Ag and invade pancreatic islets. As such, loss of BTK does not significantly reduce diabetes incidence in 125Tg/NOD mice as it does in NOD mice with a normal B cell repertoire. Thus, BTK targeting may not impair autoreactive anti-insulin B cell function, yet it may provide protection in an endogenous repertoire by decreasing the relative availability of mature autoreactive B cells.

Bruton’s Tyrosine Kinase Synergizes with Notch2 To Govern Marginal Zone B Cells in Nonobese Diabetic Mice

“…Anti-insulin B cells expressed in the 125Tg model rely on both H chain and L chain transgenes, and are critically dependent on BTK as they fail to mature into either MZ or FO cells in its absence (30). Expression of the HC transgene alone (V H 125) generates a broad repertoire in which endogenous light chains pair with the V H 125Tg (21, 31, 32).…”

“…Of note, anti-insulin 125Tg B cells (in which both anti-insulin H and L chain transgenes are expressed, Fig. 2) are highly dependent on BTK, and both FO and MZ B cells are depleted by greater than 95%, regardless of background strain (30). Thus, fine-tuned differences in BCR specificity affect reliance on BTK for MZ selection, and further affects reliance on BTK for survival.…”

Targeting Anti-Insulin B Cell Receptors Improves Receptor Editing in Type 1 Diabetes–Prone Mice

“…VH125Tg/NOD (22) and VH125Tg/Vκ125 SDNeo (36) mice were described previously. EIIA-Cre C57BL/6 (B6) mice (kindly provided by Dr. Richard Breyer, Vanderbilt University, Nashville, TN) were intercrossed with Vκ125 SDNeo B6 mice to remove the loxP-flanked Neo R cassette to generate Vκ125 SD mice (37).…”

“…Cells were subsequently stained for flow cytometry analysis, including 7-aminoactinomycin D (7-AAD) and Ab reagents reactive with CD21 (7G6), CD23 (B3B4), CD43 (S7), B220 (6B2), Igκ (187.1), Igλ (R26-46), IgM a (DS-1), IgM b (AF6-78) (BD Biosciences or eBioscience), or IgM (µ chain specific, Invitrogen). Human insulin (Sigma-Aldrich) was biotinylated (36) and was used to detect insulin-binding specificity. Avidin-fluorochrome conjugates (BD Biosciences) were used to detect biotinylated reagents.…”

Regulation of B lymphocytes and plasma cells by innate immune mechanisms and stromal cells in rheumatoid arthritis

“…The caveat of this approach is that chemokines lack sharp delimitations regarding their cell type exclusivity, and many have pleiotropic effects difficult to restrict and predict. Finally, we should consider that autoreactive B cells may also exhibit different signaling properties that make them more susceptible to certain types of therapeutic intervention [161] .…”