Interleukin-20 receptor A (IL20RA) binds to Interleukin-20 receptor B (IL20RB) (Blumberg et al. 2001, Parrish-Novak et al. 2002, Logsdon et al. 2012, Rutz et al. 2014, Dumoutier et al. 2001).
This is a black box event because it is not clear whether the dimeric receptor can form in the absence of ligand.