Inhibition of Macrophage Recruitment to Heart Valves Mediated by the C-C Chemokine Receptor Type 2 Attenuates Valvular Inflammation Induced by Group A Streptococcus in Lewis Rats.

Background: Rheumatic heart disease (RHD) is an autoimmune disease caused by recurrent infections of Group A streptococcus (GAS), ultimately leading to inflammation and the fibrosis of heart valves. Recent studies have highlighted the crucial role of C-C chemokine receptor type 2-positive (CCR2⁺) macrophages in autoimmune diseases and tissue fibrosis. However, the specific involvement of CCR2⁺ macrophages in RHD remains unclear.

Methods: This study established an RHD rat model using inactivated GAS and complete Freund's adjuvant, demonstrating a correlation between CCR2⁺ macrophages and fibrosis in the mitral valves of these rats.

Results: Intraperitoneal injection of the CCR2 antagonist Rs-504393 significantly reduced macrophage infiltration, inflammation, and fibrosis in valve tissues of RHD rats compared to the solvent-treated group . Existing evidence suggests that C-C motif chemokine ligand 2 (CCL2) acts as the primary recruiting factor for CCR2⁺ cells. To validate this, human monocytic leukemia cells (THP-1) were cultured in vitro to assess the impact of recombinant CCL2 protein on macrophages. CCL2 exhibited pro-inflammatory effects similar to lipopolysaccharide (LPS), promoting M1 polarization in macrophages. Moreover, the combined effect of LPS and CCL2 was more potent than either alone. Knocking down CCR2 expression in THP-1 cells using small interfering RNA suppressed the pro-inflammatory response and M1 polarization induced by CCL2.

Conclusions: The findings from this study indicate that CCR2⁺ macrophages are pivotal in the valvular remodeling process of RHD. Targeting the CCL2/CCR2 signaling pathway may therefore represent a promising therapeutic strategy to alleviate valve fibrosis in RHD.