Multiple changes in VLA protein glycosylation, expression, and function occur during mouse T cell ontogeny.

VLA molecules (beta 1 integrins) are cell-surface alpha beta heterodimers that bind to extracellular matrix (ECM) proteins such as fibronectin, laminin, and collagen. We analyzed the expression, structure, and function of VLAs on mouse thymocytes, as a first step toward understanding their role in T cell development. Two major forms of beta 1 were detected, which differed in their extent of N-glycosylation and sialylation. No evidence for alternative splicing of beta 1 mRNA was obtained by PCR analyses. The larger (135 kDa, nonreduced) more basic beta 1 was the only form on nonmature (J11d+) adult thymocytes, with 135 kDa and larger beta 1-chains expressed on fetal thymocytes from day 14 of gestation through birth. The smaller (120 kDa, nonreduced), more acidic beta-chain was found exclusively on mature (J11d-) thymocytes and peripheral lymphocytes. VLA alpha-chain expression was also analyzed. Virtually all thymocytes were VLA-alpha 4+, -alpha 6+. VLA-alpha 5 was detected in both J11d+ and J11d- thymocytes by immunoprecipitation, but could not be analyzed in detail because of the lack of an appropriate mAb for flow cytometry. VLA-alpha 1 and -alpha 2 were immunoprecipitated only from cells within the J11d- population. Only J11d+ thymocytes (12 to 15%) bound to fibronectin (via VLA-4 and VLA-5) and binding to laminin (via VLA-6) was two to fourfold higher in J11d+ compared with J11d- thymocytes (60 to 80% vs 20 to 30%). The high percentage of J11d+ thymocytes adhering to laminin suggests that VLA-6 exists in an activated state on most thymocytes, in contrast to resting peripheral T cells. These data show that major changes in VLA glycosylation, expression, and ECM-binding capacity occur as thymocytes mature, supporting the hypothesis that VLA-ECM interactions play a role in T cell ontogeny.