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Localization of peptide/MHC class II complexes in macrophages following antigen processing of viable Streptococcus
Alexei von Delwig1, Lakshmi Ramachandra, Clifford V Harding
1School of Clinical Medical Sciences (Rheumatology), University of Newcastle upon Tyne, Newcastle upon Tyne, GB.
Abstract:
The subcellular localization of peptide/MHC complexes was investigated during processing of the surface M5 protein from Streptococcus pyogenes. Bone marrow-derived macrophages were pulsed with viable S. pyogenes for 20 min followed by various periods of chase. T hybridoma cells detected complexes of one epitope, M5(17-31) with E(d) on the surface of macrophages within 30 min of chase. In contrast, complexes with another epitope, M5(308-319) with A(d) peaked later. Intracellular localization of peptide/MHC-II complexes was studied by subcellular fractionation and detection of complexes in fractions by T hybridoma cells. M5(17-31)/E(d) complexes were detected in light membrane fractions containing plasma membrane and early endosomes by 10-30 min. M5(308-319)/A(d) complexes were detected in these light membranes after 3 h of chase. Thus, the time course of M5(308-319)/A(d) presentation was delayed relative to M5(17-31)/E(d). However, neither type of complex was detected at any time in fractions containing phagosomes. Both species of peptide/MHC complexes localized to endocytic compartments, indicating a role for endosomes in presentation of antigens from phagocytosed bacteria.
Insights
This study reveals how Streptococcus pyogenes M5 protein fragments are presented by macrophages. Peptide/MHC complexes are found in endosomes, not phagosomes, indicating endosomes
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Streptococcus pyogenes is a significant human pathogen.
- Understanding antigen processing and presentation is crucial for vaccine development and immune response modulation.
Purpose of the Study:
- To investigate the subcellular localization of peptide/MHC complexes during the processing of Streptococcus pyogenes M5 protein.
- To determine the cellular compartments involved in the presentation of M5-derived peptides.
Main Methods:
- Bone marrow-derived macrophages were incubated with viable S. pyogenes.
- Subcellular fractionation and T hybridoma cell assays were used to detect peptide/MHC complexes.
Main Results:
- Two distinct peptide/MHC class II complexes, M5(17-31)/E(d) and M5(308-319)/A(d), were detected.
- M5(17-31)/E(d) complexes appeared on the cell surface and in early endosomes within 30 minutes.
- M5(308-319)/A(d) complexes showed a delayed presentation, appearing after 3 hours, and were also found in endocytic compartments.
Conclusions:
- Antigen processing of S. pyogenes M5 protein involves distinct pathways for different epitopes.
- Peptide/MHC complexes are localized to endocytic compartments, specifically endosomes, rather than phagosomes.
- Endosomes play a critical role in the presentation of antigens derived from phagocytosed bacteria.