Abstract
Basophils co-express FcεRIα and CD49b, the α-2 chain of integrin-type receptor VLA-2 (α2β1), which recognizes type-1 collagen as a major natural ligand. The physiological relevance of this integrin for interactions with extracellular bone marrow matrix remains unknown. Herein, we examined the expression of several receptors of this family by bone marrow-derived basophils sorted either ex-vivo or after culture with IL-3. Having established that both populations display CD49d, CD49e and CD49f (α-4, α-5 and α-6 integrins subunits, respectively), we addressed receptor functions by measuring migration, adhesion, proliferation and survival after interacting with matched natural ligands. Type I collagen, laminin and fibronectin promoted basophil migration/adhesion, the former being the most effective. None of these ligands affected basophil viability and expansion. Interactions between basophils and extracellular matrix are likely to play a role in situ, as supported by confocal 3D cell imaging of femoral bone marrow sections, which revealed basophils exclusively in type-1 collagen-enriched niches that contained likewise laminin and fibronectin. This is the first evidence for a structure/function relationship between basophils and extracellular matrix proteins inside the mouse bone marrow.
Highlights
Basophils are rare, circulating cells that have long been ignored, because of the lack of reliable methods of identification
Using confocal microscopy on femoral bone marrow sections, we found that basophils reside in particular niches of the bone marrow, forming close contacts with type I collagen, laminin and fibronectin
We looked for the possible effect of extracellular matrix (ECM) ligands on proliferation and/or differentiation of the basophil lineage by determining the relative basophil (CD49b+FceRIa+ cells) counts generated from bone marrow cells cultured for 8 days with IL-3 with or without ECM ligands (10 mg/mL)
Summary
Basophils are rare, circulating cells that have long been ignored, because of the lack of reliable methods of identification. We carried out two independent experiments for detecting integrin chain transcripts, using in both cases the qPCR strategy, we only applied one condition of basophil enrichment, namely cell sorting of IL-3-induced bone marrow cell cultures.
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