Siqi Li ,Tianfeng Chen ,Kexin Gao ,Yong-Bo Yang ,Baojie Qi ,Chunsheng Wang ,Tongqing An ,Xuehui Cai ,Shujie Wang

Microorganisms.2024 Sep 12;12(9):1879.doi: 10.3390/microorganisms12091879.

Abstract

Streptococcus suis  is an important bacterial pathogen that affects the global pig industry. The immunosuppressive nature of  S. suis  infection is recognized, and our previous research has confirmed thymus atrophy with a large number of necrotic cells. In this current work, we aimed to uncover the role of pyroptosis in cellular necrosis in thymic cells of  S. suis -infected mice. Confocal microscopy revealed that  S. suis  activated the M1 phenotype and primed pyroptosis in the macrophages of atrophied thymus. Live cell imaging further confirmed that  S. suis  could induce porcine alveolar macrophage (PAM) pyroptosis in vitro, displaying cell swelling and forming large bubbles on the plasma membrane. Meanwhile, the levels of p-p38, p-extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) were increased, which indicated the mitogen-activated protein kinase (MAPK) and AKT pathways were also involved in the inflammation of  S. suis -infected PAMs. Furthermore, RT-PCR revealed significant mRNA expression of pro-inflammatory mediators, including interleukin (IL)-1β, IL-6, IL-18, tumor necrosis factor (TNF)-α and chemokine CXCL8. The data indicated that the inflammation induced by  S. suis  was in parallel with pro-inflammatory activities of M1 macrophages, pyroptosis and MAPK and AKT pathways. Pyroptosis contributes to necrotic cells and thymocyte reduction in the atrophied thymus of mice.

Keywords: M1 macrophages; Streptococcus suis; inflammation; pyroptosis.