Differential utilization of VLA-4 (alpha 4 beta 1) and -5 (alpha 5 beta 1) integrins during the development of mouse bone marrow-derived mast cells.

Cytokines have been shown to have major roles in the development of mast cells from bone marrow progenitors. Immature mast cells derived from bone marrow thus leave the blood system to complete their course of maturation within tissues. However, it is now clear that VLA (beta 1) integrins with function in mediating cell-cell and cell-extracellular matrix protein interactions have effects on the growth and differentiation of diverse cell types. At present, the involvement of VLA integrins during mast cell development is still unclear. In this study, we report the preparation of a new monoclonal antibody (mAb) against mouse VLA-5 (alpha 5 beta 1) integrin. Together with mAb R1-2, we characterized the expression of VLA-4 (alpha 4 beta 1) and VLA-5 integrins, the two major fibronectin receptors, on two long-term cultured mast cell lines, CFTL-15 and MC/9. CFTL-15 cells were found to express both VLA-4 and -5 integrins whereas MC/9 cells expressed only VLA-5 but not VLA-4. We speculated that VLA integrin expression may be related to mast cell development. Thus bone marrow-derived mast cells (BMMC) were characterized after varying periods of development induced by IL-3. During the first 3 weeks the expression of VLA-4 and VLA-5 increased progressively and both were involved in mediating adhesion of BMMC to fibronectin. At time periods of greater than 3 weeks, the expression of VLA-4 declined gradually to little, if any, by week 13. In comparison, VLA-5 remained stably expressed and functioned as the major receptor for fibronectin. Results from this study therefore suggest that BMMC differentially utilize VLA-4 and VLA-5 integrins during IL-3-induced development. Differential expression of VLA integrins may have effects on the recirculation properties, tissue distribution and eventual maturation of progenitors to fully matured mast cells.