INTEGRIN VLA-6 (ALPHA-6-BETA-1) IS TRANSIENTLY EXPRESSED DURING THE DEVELOPMENT OF MOUSE BONE-MARROW-DERIVED MAST-CELLS

In the present study the involvement of VLA-6 (alpha 6 beta 1) integri n, a laminin receptor, was characterized during the course of mouse bo ne marrow-derived mast cell (BMMC) development. Flow cytometry and imm unoprecipitation revealed increases in alpha 6 integrin expression dur ing the first 3 weeks, followed by a decline, such that alpha 6 beta 1 was no longer detectable by week 13. Using RT-PCR, transcripts for al pha 6A but not the alpha 6B isoform were detected. Results from immuno precipitation and costaining with beta 1- or beta 4-specific mAb showe d the expression of VLA-6 (alpha 6 beta 1) and not alpha 6 beta 4 hete rodimers. Moreover, the ability of BMMC to interact with laminin corre lated with the time period of VLA-6 expression. However, only 40% of a dhesion to laminin was inhibited by blocking mAb for alpha 6, indicati ng the involvement of additional laminin receptor(s). This is supporte d by the immunoprecipitation of VLA-2 integrin, also known to have lam inin binding properties. Heterogeneity of VLA-6 expression was also fo und in connective tissue-type mast cells; thus, VLA-6(hi) and VLA-6(lo ) subpopulations of peritoneal mast cells were observed. The heterogen eity 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 ma st cell precursors to migrate and complete their course of maturation within tissues.