Integrin VLA-6 (α6β1) is transiently expressed during the development of mouse bone marrow-derived mast cells

In the present study the involvement of VLA-6 (α6β1) integrin, a laminin receptor, was characterized during the course of mouse bone marrow-derived mast cell (BMMC) development. Flow cytometry and immunoprecipitation revealed increases in α6 integrin expression during the first 3 weeks, followed by a decline, such that α6β1 was no longer detectable by week 13. Using RT-PCR, transcripts for α6A but not the α6B isoform were detected. Results from immunoprecipitation and costaining with β1-or β4-specific mAb showed the expression of VLA-6 (α6β1) and not α6β4 heterodimers. Moreover, the ability of BMMC to interact with laminin correlated with the time period of VLA-6 expression. However, only 40% of adhesion to laminin was inhibited by blocking mAb for α6, indicating the involvement of additional laminin receptor(s). This is supported by the immunoprecipitation of VLA-2 integrin, also known to have laminin binding properties. Heterogeneity of VLA-6 expression was also found in connective tissue-type mast cells; thus, VLA-6hi and VLA-6lo subpopulations of peritoneal mast cells were observed. The heterogeneity of VLA-6 integrin expression in BMMC and CTMC may be relevant to the concept of mast cell heterogeneity as well as to the ability of mast cell precursors to migrate and complete their course of maturation within tissues.