Cellular heterogeneity of MKs within the BM and of MKs present in the lung. MK subgroups within the BM. (A) Proplatelet-forming MKs close to the sinuous blood vessels are high in expression of Tubb1, Vwf,¹⁴ and MYH9.⁵¹ (B) Immunoregulatory MK subpopulation presenting MHC-II⁵³ and CD18,⁵⁸ which are responsible for the interaction with lymphocytes and neutrophils, respectively. Immunoregulatory MKs are high in expression of Chil1, Ctss,¹⁴ and CCL3,⁵¹ and secrete cytokines. (C) MKs, with suggested hematopoietic stem cell niche and osteogenic niche supporting a role evident in the high expression of Tgfb1, Egf1, COL1A3.⁵¹ (D) Subset of actively cycling MKs expressing Pola2, Pold1,¹⁴ and CCND1.⁵⁰ (E) The lung contains MKs with an immunoregulatory phenotype expressing Ccr7, Hla-Drb1, and Icam1,¹³ in addition to intravascular MKs.⁶⁹