Murine Bone Marrow-Derived Megakaryocytes Are Capable of Antigen Cross-Presentation on Major Histocompatibility Class (MHC) I Molecules
Bibliographic record
Abstract
Abstract Major Histocompatibility complex (MHC) class I is a complex composed of two proteins, the MHC-encoded alpha heavy chain and the beta2-microglobulin light chain. In the endoplasmic reticulum, it receives an antigen peptide of usually eight to eleven residues in its groove and is exported to the plasma membrane. In classical MHC class I presentation, endogenous antigens are presented to CD8+ T cells. On the other hand, cross-presentation consists in the presentation of exogenously-derived proteins in the context of MHC class I molecules to CD8+ T lymphocytes, inducing a cytotoxic response against the antigen presenting cell (APC). Platelets have been previously shown to be able to cross-present immunogenic ovalbumin (OVA) peptides, as well as bacterial peptides and to trigger CD8+ T lymphocyte activation. It is thought that the antigen cross presenting function of platelets is transmitted from megakaryocytes (MK) during thrombopoiesis, but whether megakaryocytes can cross-present is still unknown. To address this question, we developed an in vitro endocytosis model of murine bone marrow-derived megakaryocytes. C57BL/6 mouse megakaryocytes are enriched by gradient sedimentation and pulsed with fluorescent ovalbumin (OVA) for various times. In addition, we used DQ-OVA, a BODIPY FL-conjugated OVA, which becomes fluorescent upon proteolysis. Cells were then analyzed by flow cytometry or confocal microscopy to assess the OVA megakaryocyte internalization, its proteolytic degradation and its loading onto MHC class I molecules. We can show the endocytosis of exogenous OVA by megakaryocytes, in a pathway involving lysosomes. The endocytosed OVA were subsequently proteolytically cleaved into the immunogenic OVA peptide SIINFEKL and the peptide is inserted into the antigen binding groove of MHC class I molecules. The MHC class I-OVA peptide complexes are stored in the MK alpha-granules and can be translocated to the plasma membrane. Thus, we have shown that MKs can effectively process and present exogenous antigens on MHC class I molecules. This opens a new avenue toward a functional characterization of this pathway and its modulation, leading to new therapeutic approaches in autoimmune diseases targeting megakaryocytes, such as immune thrombocytopenia (ITP). Disclosures No relevant conflicts of interest to declare.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".