Encapsulated group BStreptococcusmodulates dendritic cell functions via lipid rafts and clathrin-mediated endocytosis

Abstract

Group B Streptococcus (GBS) capsular type III is an important agent of life-threatening invasive infections. It has been previously shown that encapsulated GBS is easily internalized by dendritic cells (DCs) and can persist inside these immune cells. The mechanisms underlying these processes are unknown. Here, colocalization studies and the use of endocytosis inhibitors and caveolin(-/-) mice, demonstrated that GBS uses multiple endocytosis mechanisms to enter mouse DCs. The capsular polysaccharide (CPS) selectively drives GBS internalization via caveolae-independent but lipid raft-dependent pathways. Non-encapsulated bacteria failed to engage lipid rafts. GBS internalization by DCs also occurs via clathrin-mediated endocytosis in a process independent of bacterial CPS. Albeit caveolae are not required for GBS internalization, signalling events through caveolin-1 are involved in production of the inflammatory chemokine CCL2 by DCs infected with encapsulated GBS only. This study addresses for the first time endocytosis pathways implicated in DC internalization of encapsulated GBS and suggests a complex interplay between GBS and DCs, which was selectively modulated by the presence of CPS.