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α-Dystroglycan has been proved to be involved in lymphocyte activation by participating in immunological synapse (IS) formation. Considering the existence of IS formation in thymic development, we questioned whether α-dystroglycan was expressed in thymus and influenced thymic development. In this study, we demonstrated that α-dystroglycan was expressed on fetal thymocytes, especially on double-positive (DP, CD4+CD8+) cells. Blocking α-dystroglycan by treatment of fetal thymus organ culture (FTOC) with anti-α-dystroglycan antibody IIH6C4 decreased the number of DP cells compared with nontreated or isotype antibody controls. Down-regulation of α-dystroglycan by retroviruses carrying antiseuse cDNA of dystroglycan in reaggregate thymus organ culture (RTOC) further confirmed these results. Enhanced apoptosis of DP cells was observed after blocking α-dystroglycan. Interestingly, we found that blocking α-dystroglycan reduced IS formation between DP cells and thymic epithelial cells. Furthermore, blocking α-dystroglycan up-regulated CD95/CD95L expression and reduced Bcl-2 expression on DP cells in the developing thymus. Finally, the increase in the apoptosis of DP cells was associated with a consequent decrease in the positive selection, as indicated by the reduction of both ERK phosphorylation in DP cells and single-positive (SP, CD4+ or CD8+) cell outcome. Altogether, these results indicated that α-dystroglycan was involved in positive selection of thymocytes by participating in the IS formation. [ABSTRACT FROM AUTHOR]

It is well established that agrin, an extracellular matrix protein, plays a crucial role in the formation of neuromuscular junctions. Recent evidence indicates that agrin also contributes to immunological synapse formation. However, little is known about how agrin induces the activation of lymphocytes and whose receptors mediate its regulatory effects on these cells. In the present study, agrin was detected in lymphocytes. Up-regulation of agrin expression was involved in lymphocyte activation whereas down-regulation of its expression led to inhibition of both antigen-specific and nonspecific lymphocyte activation, indicating an intrinsic role for agrin in the activation of lymphocytes. Unexpectedly, unlike that found in muscle cells where there is coexpression of muscle-specific kinase (MUSK) and α-dystroglycan receptors for agrin, only α-dystroglycan could be detected in lymphocytes. Confocal examination showed that α-dystroglycan colocalized with agrin in forming the immunological synapse. Down-regulation of α-dystroglycan expression inhibited lymphocyte activation even in the presence of agrin. However, agrin involved in down-regulation of α-dystroglycan receptors did not increase the inhibitory effect on lymphocytes activation. The anti-α-dystroglycan antibody also induced lymphocytes activation. Taken together, these findings strongly indicate that agrin and α-dystroglycan mediate lymphocyte activation. Furthermore, agrin-involved lymphocyte activation is mediated by α-dystroglycan. [ABSTRACT FROM AUTHOR]