Abstract: Objective To investigate whether interleukin-37 (IL-37) affects macrophage M1 polarization via nucleotide oligomerization of structural domain receptor protein 1 (NOD1)/nuclear factor κB (NF-κB) in plasma cell mastitis. Methods A total of 15 patients with plasma cell mastitis were recruited according to the collection standard as inflammatory breast tissue and normal breast tissue with a distance of ≥3 cm from the edge of the inflammatory breast tissue. QPCR was performed to detect NOD1 and IL-3. Phorbol ester(PE) was used to induce THP-1 cells to differentiate into resting macrophages (M0). Lipopolysaccharide (LPS) combined with interferon(IFN-γ) was used to induce the polarization of M0 macrophages towards the M1 phenotype. NOD1 lentiviral RNA interference or over-expression vectors were constructed to regulate the expression of NOD1 in M1 macrophages. M0 macrophages were pretreated with IL-37 recombinant protein and then incubated with LPS and IFN-γ for induction. The expression of NOD1, IL-37, M1 markers (IL-6 and iNOS) and M2 markers (IL-10 and Arg-1) was quantified by qPCR. Western blot was employed to assess the protein level of NOD1, NF-kB p65, and p-NF-kB p65. Co-immunoprecipitation was used to detect the interaction between NOD1 and IL-37. Results Up-regulation of NOD1 and down-regulation of IL-37 as were found in inflammatory breast tissues(P＜0.05). Compared to M0 cells, M1 cells showed up-regulated NOD1 and M1 markers and the elevated phosphorylated NF-κB p65 but the down-regulated IL-37(P＜0.05). In M1 macrophages, both NF-κB inhibitor and NOD1 knockdown led to the down-regulation of NOD1 and M1 markers and caused a decrease in the phosphorylated NF-κB p65(P＜0.05). IL-37 recombinant protein decreased phosphorylation of NOD1, M1 marker and NF-κB p65, which was reversed by over-expression of NOD1. IL-37 may interact with NOD1(P＜0.05). Conclusions IL-37 may inhibit M1 polarization in macrophages by down-regulating NOD1/NF-κB pathway thereby preventing plasma cell mastitis progression.

Key words: plasma cell mastitis, macrophage, M1 polarization, interleukin-37, nucleotide oligomerization structural domain receptor protein 1