Correlation of AHR Activation-Induced Suppression of PWM-Stimulated IgG and IgG-Triggered Signaling in Human PBMCs

Background/Objectives: Aryl hydrocarbon receptor (AHR) ligands are known to suppress antibody production. However, it remains unclear whether this suppression translates into altered antibody-mediated Fcγ receptor signaling in human cells. This study aimed to investigate the effects and mechanisms by which AHR ligands regulate antibody production and antibody-triggered responses in human peripheral blood mononuclear cells (PBMCs). Methods: PBMCs were isolated from blood obtained from anonymous healthy donors. PBMCs were stimulated with pokeweed mitogen (PWM) to induce IgG1 production or Strept-Biotin IgG1/IgG2 immune complexes to induce antibody-triggered signaling. Before any stimulation, cells were pretreated with vehicle (0.01% DMSO) or AHR ligands TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), ITE (2-(1H-indol-3-ylcarbonyl)-4-thiazolecarboxylic acid methyl ester), or FICZ (6-formylindolo[3,2-b]carbazole), or the proligand I3C (indole-3-carbinol). Results: Our data revealed that PWM stimulation significantly increased IL6 and IL1B gene expression and PWM-induced IL-6 cytokine secretion, which was significantly suppressed by TCDD, ITE, FICZ, and I3C. However, only TCDD was able to suppress PWM-stimulated IgG1 antibody production. Transcriptomic analysis using I3C revealed upregulated AHR-responsive genes such as CYP1A1, CYP1B1, AHRR and TIPARP in PWM-stimulated human PBMCs. Notably, I3C downregulated genes TRAPPC9 and C1QTNF3, which play a role in NF-κB-associated inflammatory signaling. It also revealed potential sex differences in I3C-mediated gene modulation associated with B cell function, Ig expression, FcγR signaling, and inflammatory pathways. Lastly, IgG1 and IgG2 immune complex-stimulated IL-6 cytokine secretion was significantly suppressed by TCDD, whereas I3C showed modest, although not statistically significant, suppression. Conclusions: Overall, these findings demonstrate that AHR activation by TCDD suppressed antibody production and IgG-mediated immune signaling in human PBMCs.