In this study, it is examined whether the organotin compound di-n-butyltindichloride (DBTC), which has been shown to inhibit immature thymocyte proliferation, is able to disturb the binding between thymocytes and thymic epithelial cells (TEC). To that end, an enzyme-linked binding assay was developed in which the amount of binding of Thy-1+ (mAb ER4)-thymocytes to the rat-derived TEC-line IT45R1 (IT45R1-TEC) could be detected. It was found that preincubation of thymocytes with 3-5 μM DBTC for 30 min inhibited the binding by 50-60% during a 1 h adhesion period. By extending the preincubation period to 1 h and the adhesion period to 22 h, 0.1 μM DBTC was already sufficient to reduce the binding with 60-80%. Further characterization of the binding revealed that splenic lymphocytes were unable to bind to the MHC class II-negative IT45R1-TEC. Since dextran sulfate inhibited the binding as well, sulfated polysaccharide-binding molecules such as Thy-I and CD2 are likely to be involved in the binding. Electron microscopy showed filament-containing microvilli at the site of interaction. The results are discussed in relation to the mechanism of DBTC-induced thymus atrophy.
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