Aberrant Host Immune Responses Specific To Microbial-derived Ligands Are Linked To Hypertension In BPH/2J Mice

It has been established that derangements in host-microbiota homeostasis leads to hypertension. However, the precise mechanisms remain largely unknown. Microbial-derived ligands released into the host circulation are sensed and eliminated by various host innate and adaptive immune mechanisms. Herein, we focused on such microbial-derived ligands and hypothesized that defect in host innate and adaptive immune response to counter microbial-derived ligands is linked to hypertension. To test this hypothesis, both in vitro and in vivo studies were conducted. First, bone marrow-derived macrophages from Blood Pressure Normal (BPN/3J, systolic blood pressure: 113.2±2.20 mm Hg) and Blood Pressure Hypertensive (BPH/2J, systolic blood pressure: 143.9±4.10 mm Hg) mice (male, 8 weeks) were challenged with various Toll-like receptor (TLR) ligands of microbial origin. Unstimulated macrophages from BPH mice displayed reduced levels of the co-stimulatory activation markers CD40, CD80 and CD86 (~2 fold) compared to macrophages from BPN/3J mice. Such differences, however, was normalized upon stimulation with ligands for TLR3 (poly-I:C), TLR4 (LPS), TLR5 (flagellin), TLR7/8 (R848) and TLR9 (CpG-DNA). Despite so, BPH-macrophages displayed blunted IL-6 and lipocalin-2 (~2 fold) levels in response to all the aforementioned TLR ligands when compared to macrophages from BPN mice. To confirm these findings in vivo , we challenged BPN and BPH mice with the microbial-derived ligand, flagellin. Interestingly, even though BPH mice had reduced cytokine responses to flagellin as monitored by levels of Lcn2 (BPN 320.9 ± 22.20 vs BPH 230.8 ± 12.40, p<0.05) and CXCL1 (BPN 40.9 ± 4.6 vs BPH 23.8 ± 2.4, p<0.05), they displayed higher levels of flagellin-specific IgG (BPN vs BPH O.D 450 , 0.51 ± 0.10 vs 0.93 ± 0.07, p<0.05) and substantially lower levels of flagellin-specific IgA (BPN vs BPH O.D 450 , 0.44 ± 0.13 v s 0.13 ± 0.03, p<0.05). Collectively, both in vitro and in vivo studies demonstrate that both innate and adaptive immune responses specifically against microbial ligands is substantially deranged in the hypertensive state.