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Neutrophils process exogenous bacteria via an alternate class I MHC processing pathway for presentation of peptides
1Department of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
Abstract:
Peptides that are presented by class I MHC (MHC-I) molecules derive from cytosolic Ags processed via the conventional MHC-I pathway or exogenous Ags processed via alternate MHC-I processing mechanisms. Alternate MHC-I processing by macrophages and dendritic cells allows presentation of peptides from particulate Ags, including bacteria. Despite the established phagocytic activity of neutrophils, MHC-I processing and presentation of phagocytosed Ags by neutrophils has not been investigated. Murine neutrophils from peritoneal exudates were shown to express MHC-I molecules and tested for the ability to process HB101.Crl-OVA, Escherichia coli transfected to express a fusion protein containing the 257-264 epitope of OVA. Neutrophils were found to process HB101.Crl-OVA and present OVA(257-264)-K(b) complexes to CD8OVA T hybridoma cells via a pathway that was resistant to brefeldin A, an inhibitor of anterograde endoplasmic reticulum-Golgi transport, and lactacystin, a proteasome inhibitor. These results suggest that neutrophils process phagocytosed bacteria via a vacuolar alternate MHC-I pathway that does not involve cytosolic processing. In addition, neutrophils were found to secrete or "regurgitate" processed peptide that was subsequently presented by neighboring prefixed macrophages or dendritic cells. Thus, neutrophils may influence T cell responses to bacteria, either by directly presenting peptide-MHC-I complexes or by delivering peptides to other APCs for presentation. Hypothetically, neutrophils may directly present peptide to effector T cells in vivo at sites of inflammation, inducing cytokine production, whereas dendritic cells in receipt of neutrophil-derived antigenic peptides may migrate to lymphoid organs to initiate T cell responses.
Insights
Neutrophils process phagocytosed bacteria via a vacuolar pathway, presenting antigens on MHC-I molecules. They also transfer processed peptides to other antigen-presenting cells, influencing T cell responses to bacteria.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Class I MHC (MHC-I) molecules present peptides from cytosolic or exogenous antigens via alternate processing pathways.
- Macrophages and dendritic cells utilize alternate MHC-I processing for particulate antigens like bacteria.
- Neutrophil MHC-I processing of phagocytosed antigens remains unexplored despite their phagocytic role.
Purpose of the Study:
- To investigate MHC-I processing and presentation of phagocytosed antigens by neutrophils.
- To determine the pathway utilized by neutrophils for antigen processing.
- To explore the role of neutrophils in antigen transfer to other antigen-presenting cells.
Main Methods:
- Murine neutrophils were isolated and tested for MHC-I expression.
- Neutrophils processed Escherichia coli engineered to express an OVA epitope (HB101.Crl-OVA).
- Antigen presentation was assessed using CD8OVA T hybridoma cells, with inhibitors of ER-Golgi transport and proteasome activity.
Main Results:
- Murine neutrophils express MHC-I molecules.
- Neutrophils successfully processed HB101.Crl-OVA and presented OVA(257-264)-K(b) complexes.
- The processing pathway was resistant to brefeldin A and lactacystin, indicating a non-cytosolic, vacuolar route.
- Neutrophils released processed peptides, which were subsequently presented by macrophages and dendritic cells.
Conclusions:
- Neutrophils process phagocytosed bacteria via a vacuolar, alternate MHC-I pathway independent of cytosolic processing.
- Neutrophils can transfer processed antigenic peptides to neighboring antigen-presenting cells.
- Neutrophils may directly present antigens to effector T cells or indirectly influence adaptive immunity by providing antigens to dendritic cells.