Altered sympathetic-to-immune cell signaling via β₂- adrenergic receptors in adjuvant arthritis

Adjuvant-induced arthritic (AA) differentially affects norepinephrine concentrations in immune organs, and in vivo β-adrenergic receptor (β-AR) agonist treatment distinctly regulates ex vivo cytokine profiles in different immune organs. We examined the contribution of altered β-AR functioning in AA to understand these disparate findings. Twenty-one or 28 days after disease induction, we examined β ₂-AR expression in spleen and draining lymph nodes (DLNs) for the arthritic limbs using radioligand binding and western blots and splenocyte β-AR-stimulated cAMP production using enzyme-linked immunoassay (EIA). During severe disease, β-AR agonists failed to induce splenocyte cAMP production, and β-AR affinity and density declined, indicating receptor desensitization and downregulation. Splenocyte β ₂-AR phosphorylation (pβ ₂-AR) by protein kinase A (pβ ₂-AR_PKA) decreased in severe disease, and pβ ₂-AR by G protein-coupled receptor kinases (pβ ₂-AR_GRK) increased in chronic disease. Conversely, in DLN cells, pβ ₂-AR_PKA rose during severe disease, but fell during chronic disease, and pβ ₂-AR_GRK increased during both disease stages. A similar pβ ₂-AR pattern in DLN cells with the mycobacterial cell wall component of complete Freund's adjuvant suggests that pattern recognition receptors (i.e., toll-like receptors) are important for DLN pβ ₂-AR patterns. Collectively, our findings indicate lymphoid organ- and disease stage-specific sympathetic dysregulation, possibly explaining immune compartment-specific differences in β ₂-AR-mediated regulation of cytokine production in AA and rheumatoid arthritis.