Roles of integrins and CD44 on the adhesion and migration of fetal liver cells to the fetal thymus

Adhesion and migration of mouse fetal liver (FL) cells to the thymus were i nvestigated using cells from green fluorescent protein transgenic (GFP(+)) mice. FL cells from GFP(+) embryos at 12 gestational days (E12) of mice wer e incubated with 2'-deoxyguanosine-treated fetal thymus lobe (from E14) by thymic repopulation (hanging drop) culture methods. GFP(+) cells were obser ved in the thymus lobe at the end of the repopulation culture period. A lar ge part of the infiltrated cells expressed CD44 until day 2 of culture on a permeable membrane, then lost the expression. CD25 expression was observed from day 1 to day 4, Around day 8, GFP(+) cells became both CD4(+) and CD8 (+). The results support the early observation of the sequential expression of CD44, CD25, and CD4/8 during the early stages of thymocyte development. When anti-CD44 mAb was added at the beginning of the repopulation culture period, GFP(+) FL cells adhered to the surface of the thymus lobe but did n ot migrate into the thymus, Pretreatment of the thymus with hyaluronidase o r hyaluronate produced results similar to the results of anti-CD44 treatmen t, On the other hand, the addition of anti-integrin alpha(4) mAb inhibited adhesion to the thymus, and almost no GFP+ cells were seen on the surface o f the thymus lobe. The data suggest that integrin alpha(4) and CD44 play di fferent roles, i.e., integrin alpha(4) is required for the adhesion of FL c ells to the thymus lobe and CD44 is required for the migration of the cells into the thymus.