Plasticity in leukocyte migration during haematopoiesis and inflammation

Under normal physiological conditions, leukocytes and other tissue resident immune cells have been shown to migrate using the mesenchymal (integrin/adhesion dependent) and/or ameboid (integrin/adhesion independent) modes of migration. The objective of this manuscript is to provide a comprehensive literature review that illustrates how leukocytes display high levels of plasticity shifting between ameboid to mesenchymal modes of migration during haematopoiesis and the inflammatory response. This plasticity is shaped by the reciprocal regulation between the pattern of gene expression associated with their haematopoietic lineage or the leukocyte activation status, and the response to the physicochemical and topological characteristics of the surrounding tissue. The use of some common elements from the F-actin polymerising and actomyosin machinery in both modes of migration may facilitate the high capacity of leukocytes to alternate between the two migration modes while navigating a highly heterogenous landscape of physicochemical cues in their anatomical journey. We discuss this paradigm using detailed examples of specific leukocyte populations such as dendritic cells, macrophages and lymphocytes. We propose that cell adhesions involved in leukocyte migration represent signalling hubs where differentiation and physicochemical cues converge. These molecular complexes then generate signalling outputs that coordinate leukocyte expansion, differentiation, and optimal patterns of cell migration during haematopoiesis and leukocyte recruitment to inflammation sites.