Publications

Interleukin 2 and interleukin 15 (IL2 and IL15, respectively) provide quite distinct contributions to T-cell-mediated immunity, despite having similar receptor composition and signaling machinery. As most of the proposed mechanisms underlying this apparent paradox attribute key significance to the individual {alpha}-chains of IL2 and IL15 receptors, we investigated the spatial organization of the receptors IL2R{alpha} and IL15R{alpha} at the nanometer scale expressed on a human CD4+ leukemia T cell line using single-molecule-sensitive near-field scanning optical microscopy (NSOM). In agreement with previous findings, we here confirm clustering of IL2R{alpha} and IL15R{alpha} at the submicron scale. In addition to clustering, our single-molecule data reveal that a non-negligible percentage of the receptors are organized as monomers. Only a minor fraction of IL2R{alpha} molecules reside outside the clustered domains, whereas [~]30% of IL15R{alpha} molecules organize as monomers or small clusters, excluded from the main domain regions. Interestingly, we also found that the packing densities per unit area of both IL2R{alpha} and IL15R{alpha} domains remained constant, suggesting a `building block' type of assembly involving repeated structures and composition. Finally, dual-color NSOM demonstrated co-clustering of the two {alpha}-chains. Our results should aid understanding the action of the IL2R-IL15R system in T cell function and also might contribute to the more rationale design of IL2R- or IL15R-targeted immunotherapy agents for treating human leukemia.

JTD Keywords: Near-field scanning optical microscopy (NSOM), Interleukin receptors IL2R, IL15R, Single-molecule detection, Nanometer-scale membrane organization