HAVCR2 and tropical spastic paraparesis: In HAM/TSP patients, alternative expressions of various inhibitory receptors, such as PD-1, CD244, and Tim-3, have been demonstrated on CD8+ T cells (Enose-Akahata et al. 2009; Abdelbary et al. 2011; Kozako et al. 2011; Manuel et al. 2013).