title: High-density lipoprotein acts as an opsonin to enhance phagocytosis of group A streptococcus by U937 cells.
abstract: We have previously demonstrated that high-density lipoprotein (HDL) can specifically bind to streptococcal collagen-like protein 1 (Scl1) of M41-type group A Streptococcus (GAS). However, the pathological or physiological significance of Scl1-HDL interaction is unknown. Here, the hypothesis that HDL acts as an opsonin to enhance phagocytosis of HDL-bound GAS by monocytes given that some scavenger receptors can mediate the endocytosis of HDL was tested by using FITC-labeled bacteria, human U937 monocytes and HDL for phagocytic assays. HDL (10 µg/mL) was found to significantly enhance internalization of M41-type (ATCC 12373) GAS by U937 cells after 60 min incubation, compared with an HDL-free group. The internalized GAS were dead after 60 min incubation with U937 cells regardless of presence and absence of HDL. Although very-low-density lipoprotein (VLDL) could specifically bind to ATCC 12373 strain, it did not promote phagocytosis of GAS. Additionally, LDL, HDL and VLDL did not enhance phagocytosis of CMCC 32198 strain because this strain did not bind to these lipoproteins. A physiological concentration of HDL (1000 µg/mL) had a similar effect. Anti-CD36 antibody completely abolished opsonic phagocytosis whereas anti-CD4 antibody did not, indicating that CD36 is the major scavenger receptor mediating the uptake of HDL-opsonized GAS by U937 cells. Furthermore, because rScl1 competitively blocked the interaction of ATCC 12373 strain with HDL recombinant Scl1 (rScl1) derived from M41-type GAS, it significantly decreased opsonophagocytosis of ATCC 12373 strain but not of CMCC 32198 strain. Therefore, our findings suggest that HDL may be an opsonin that enhances CD36-dependent opsonophagocytosis of GAS by U937 cells.
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Lulei
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Yuxin
authors.initials: Y
authors.lastname: Li
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.|Key Laboratory of Animal Clinic Diagnosis and Treatment (Ministry of Agriculture of China), Inner Mongolia Agricultural University, Huhhot, China.
authors.forename: Wencheng
authors.initials: W
authors.lastname: Bai
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Na
authors.initials: N
authors.lastname: Liu
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Wenlong
authors.initials: W
authors.lastname: Li
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Yumin
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Research Center of Plasma Lipoprotein Immunology.|Key Laboratory of Animal Clinic Diagnosis and Treatment (Ministry of Agriculture of China), Inner Mongolia Agricultural University, Huhhot, China.
authors.forename: Runlin
authors.initials: R
authors.lastname: Han
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology; D018955:CD36 Antigens / Q000235:genetics / Q000276:immunology; D003094:Collagen / Q000235:genetics / Q000276:immunology; D006801:Humans; D008075:Lipoproteins, HDL / Q000276:immunology*; D009000:Monocytes / Q000276:immunology; D009895:Opsonin Proteins / Q000276:immunology*; D010587:Phagocytosis; D013290:Streptococcal Infections / Q000276:immunology* / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000235:genetics / Q000276:immunology*; D020298:U937 Cells
chemical_list: D001426:Bacterial Proteins; D018955:CD36 Antigens; D008075:Lipoproteins, HDL; D009895:Opsonin Proteins; C423454:Scl1 protein, Streptococcus; D003094:Collagen
keywords: group A Streptococcus; high-density lipoprotein; opsonin; phagocytosis