Activated leukocyte cell adhesion molecule (ALCAM/CD166), a member of the immunoglobulin superfamily, is overexpressed on the surface of HTLV-1-infected lymphocytes, both in chronically infected cell lines and in primary CD4+CD25+ T cells from HAM/TSP patients (Curis et al., 2016). Here, CD4 is linked to tropical spastic paraparesis.