IL-4 analyses could reveal that IgG from HAM/TSP and ATLL could reduce the frequency of IL-4-producing CD4+ T cells compared to other conditions, and the evaluation of IL-10 production indicates that IgG from ACs induces the production of IL-10 by CD4+ T cells compared to all other conditions (Figure 1B and Supplementary Figure S2). Here, CD4 is linked to tropical spastic paraparesis.