Here we use Microfluidic Diffusional Sizing (MDS) on a Fluidity One instrument to assess the hydrodynamic radius (Rh) over a dilution series. The tests use a commercially available lyophilized form with no additives. We observe that the Rh increases with increasing concentration, in a manner which indicates a monomer-trimer equilibrium with positive cooperativity.
This result challenges much of the modern literature which assumes a monomeric form, or in some instances a dimer. One study by Siddarth et al uses analytical ultracentrifugation and produced data which cannot rule out a monomer-trimer equilibrium, though a monomer-dimer model is eventually concluded. It should be noted that a different IL-2 source and buffer is used in this study.
For more information read the full application note here