Considering the proportion of CD4 T cells among PBMCs for the different donors, we estimated that 20–30% of the LTB4 spontaneously released by PBMCs is produced by CD4 T cells in HACs; in HAM/TSP, secretion by CD4 T cells accounts for 80% of the LTB4 released by PBMCs. This evidence concerns the gene CD4 and tropical spastic paraparesis.