Differential potency of two crosslinking plant lectins to induce formation of haptenic-sugar-resistant aggregates of rat thymocytes by post-binding signaling.

To evaluate the significance of post-binding events for stable aggregate formation, the aggregation/dissociation of rat thymocytes initiated by two crosslinking plant lectins, namely concanavalin A (Con A) and Solanum tuberosum agglutinin (STA), were comparatively studied. Despite intimate cell contacts in the aggregates only Con A led to establishment of haptenic-sugar-resistant (HSR) complexes. The presence of inhibitor II of diacylglycerol kinase, a dual calmodulin antagonist/protein kinase C inhibitor (trifluoperazine), and a sulfhydryl group reagent (N-ethylmaleimide) impaired this process. The obtained results indicate that the formation of HSR cellular contacts is not an automatic response to lectin-dependent cell association. In contrast to STA, Con A binding elicits this reaction with involvement of diacylglycerol kinase, protein kinase C and/or calmodulin as well as thiol level perturbation, as inferred by the application of target-selective inhibitors.