Cutting Edge: IL-21 and Tissue-Specific Signals Instruct Tbet+CD11c+ B Cell Development following Viral Infection

Abstract

Tbet+CD11c+ B cells, also known as age-associated B cells (ABCs), are pivotal contributors to humoral immunity following infection and in autoimmunity, yet their in vivo generation is incompletely understood. We used a mouse model of systemic acute lymphocytic choriomeningitis virus infection to examine the developmental requirements of ABCs that emerged in the spleen and liver. IL-21 signaling through STAT3 was indispensable for ABC development. In contrast, IFN-γ signaling through STAT1 was required for B cell activation and proliferation. Mice that underwent splenectomy or were deficient in lymphotoxin α generated hepatic ABCs despite the lack of secondary lymphoid organ contributions, suggesting that the liver supported de novo generation of these cells separately from their development in lymphoid organs. Thus, IFN-γ and IL-21 signaling have distinct, stage-specific roles in ABC differentiation, while the tissue microenvironment provides additional cues necessary for their development.

Figure 1.. IFN-γ and IL-21 play distinct roles in driving genesis of ABCs.

(A,B) CD44 and Ki67 expression in B220⁺ CD19⁺ and CD11c and Tbet expression in B220⁺ CD19⁺ CD44^hi Ki67⁺ splenocytes in mice at day 10 p.i. with i.p. LCMV (A) with quantification (B). (C) Expression of Tbet and CD11c in B220⁺ CD19⁺ CD44^hi Ki67⁺ splenocytes. (D) Frequencies and numbers of splenic ABCs. (E) Model. Data representative of two independent experiments with 5 or 6 mice per group. Means ± SEM, one-way ANOVA.

Figure 2.. STAT1-STAT3 interactions in ABCs following viral infection.

(A,B) CD44 and Ki67 expression in B220⁺ CD19⁺ and CD11c and Tbet expression in B220⁺ CD19⁺ CD44^hi Ki67⁺ splenocytes in mice at day 10 p.i. with i.p. LCMV or uninfected Mb1^Cre mice (A) with quantification (B). (C) Expression of Tbet and CD11c in B220⁺ CD19⁺ CD44^hi Ki67⁺ splenocytes. (D) Frequencies and numbers of splenic ABCs. (E-G) Tbet and CD11c expression of purified cultured B cells. (H) Model. Data pooling two experiments representative of four independent experiments each with 2 to 6 mice per group(A-D) or representative of three experiments with 2 to 3 biological replicates (E-G). Means ± SEM, B-D: one-way ANOVA, E-G: two-way ANOVA.

Figure 3.. Tissue environments contribute to organ-specific generation of ABCs.

(A) CD11c and Tbet expression in B220⁺ CD19⁺ CD44^hi cells and quantifications of ABCs from LNs and spleens of Tbet-AmCyan reporter mice at day 10 p.i. with i.v. LCMV. (B) 5x10⁶ of CD45.1 purified splenic B cells and 5x10⁶ of CD45.2 purified LN B cells were transferred into CD45.1/CD45.2 MD4 recipient mice 24 hours prior to i.p. infection with LCMV. Percentage of each population among total transferred cells in total splenic B cells (left) and ABCs (right). Data representative of two independent experiments with 4 to 5 mice per group (A) or with 4 to 7 mice per group (B). Means ± SEM, one-way ANOVA.

Figure 4.. Hepatic ABCs arise from circulating B cells following viral infection.

(A) Saline and FTY720 administration to Tbet-AmCyan reporter mice following i.v. LCMV infection and Tbet⁺CD11c⁺ B cell numbers at day 10 p.i. (B-D) CD11c and Tbet expression of liver B220⁺ CD19⁺ CD44^hi cells (top of B and D) and frequencies and numbers of hepatic ABCs (bottom of B and D). Data are representative of three independent experiments (A), or two independent experiments with 2 to 5 mice per group (B-D). Means ± SEM, one-way ANOVA.