Mast cells, basophils, and eosinophils: distinct but overlapping pathways for recruitment

Mast cells, basophils and eosinophils are bone marrow-derived cells that contribute to a variety of allergic and other immune responses. For example, they are relatively abundant at mucosal sites where allergic inflammation is occurring, and their activation and release of preformed and newly-generated mediators at these sites is considered central to the pathophysiology of allergic diseases. Given their involvement in allergic and other diseases, it is important to understand how these cells are selectively recruited into tissues. These cells share many phenotypic features, including those involved in adhesion and migration, yet their localization within a given tissue can be quite distinct. In addition, there are examples of selective recruitment of one cell type without the others. From studies with human cells, it is now clear that mast cells, basophils and eosinophils share a number of recruitment pathways with one another and with other cells, but that each possesses unique adhesion and migration responses that can contribute to their preferential accumulation. This review will focus on cell surface structures implicated in adhesion and migration responses of human mast cells, basophils and eosinophils. Both shared and selective expression of these molecules will be highlighted, as well as differences in their relative levels of expression. Cell type-specific stimuli that alter adhesion and migration responses will also be considered.