Abstract Body (Do not enter title and authors here): Background: Hypomorphic c-myb mice (with reduced B cells) manifest low baseline blood pressure [BP], increased 24-h urinary sodium and water excretion, and protection from DOCA salt-induced hypertension [HTN]. Here we study B cell dynamics and their role in angiotensin [Ang]-II-induced HTN using tissue flow cytometry [FC] and diphtheria toxin [DT]-induced B cell depletion in CD19-Cre/R26-iDTR mice.

Methods & Results: To investigate B cell dynamics in HTN, wild-type [WT] C57BL/6J male mice aged 10-12 wk were implanted with either (a) 500 ng/kg/min x 28-d (low-dose) or (b) 1000 ng/kg/min x 28-d (high-dose) Ang-II, or (c) saline for FC of all B cell subsets in aorta, spleen, and bone marrow. CD19⁺ B cells in aorta increased 9.3-fold with low-dose (1.5±0.9E² vs. 1.4E⁴ cells/aorta; N=1-4/group; p<0.01) and 8-fold with high-dose of Ang-II (1.5±0.9E² vs. 1.2±0.4E⁴; N=2-4/group; p<0.01). In spleen, CD138⁺ plasma cells increased 3.4-fold with low-dose- (2.1±0.3E⁵ vs. 7.2E⁵cells/spleen; N=1-4/group; p<0.001) but not with high-dose Ang-II (2.1±0.3E⁵ vs. 1.3±0.1E⁵; N=2-4/group; p=0.14). In bone marrow, plasma cells decreased 4-fold with low-dose (2.3±0.3E⁶ vs. 0.59±0.6E⁶ cells/bone marrow; N=2-4/group; p<0.05) but increased 2.2-fold with high-dose-Ang-II (2.3±0.3E⁶ vs. 5.2±0.9E⁶ cells/bone marrow; N=2-4/group; p<0.01). Then, 10-12-wk old male CD19-Cre/R26-iDTR mice and R26-iDTR controls were implanted with osmotic minipumps to deliver Ang-II (500 ng/kg/min) over 28-d. Intraperitoneal DT (25 ng/g) was injected weekly x 4 to both groups. Flow cytometry [FC] of blood and spleen at d-28 confirmed successful depletion of all B cell subsets in CD19-Cre/R26-iDTR but not R26-iDTR controls. BP measurements at d-28 showed attenuated HTN in B cell-depleted mice compared to non-depleted controls (94±15 vs. 134±12 mmHg; N=5/group; p<0.05). Metabolic studies revealed only non-B cell depleted mice to have increased 24-h Na⁺ and urine excretion in response to Ang-II (N=4/group).

Conclusion: CD19⁺ B cells infiltrate aorta during Ang-II-induced HTN. Ang-II levels regulate peripheral plasma cell homeostasis possibly through migration from/to or expansion within bone marrow and spleen. B cell depletion in the CD19-Cre/R26-iDTR model demonstrates the importance of B cell subtypes in the pathogenesis of Ang-II-induced HTN, suggesting a potential therapeutic strategy for HTN.