Megakaryocytes Direct CD4 +T Cell Responses Via Major Histocompatibility Complex Class II Antigen Presentation

Megakaryocytes (MKs) are rare, large, hematopoietic cells that canonically have the role of producing platelets. Advances in single-cell RNA-sequencing (scRNA-seq) have revealed a previously under-appreciated degree of MK heterogeneity suggesting that both murine and human MKs may perform functions beyond platelet production. Among other inflammatory molecules, these studies identified that select MK subsets express major histocompatibility complex (MHC II) antigen presentation-associated transcripts and display an upregulation of antigen processing pathways. Together, these findings suggest a potential immunoregulatory function of select MK subsets. However, functional validation substantiating these transcriptional signatures and the proposed MK immunoregulatory capacities has lagged, and the expression of MHC II in bone marrow MKs remains controversial.