Taken together, these results imply that increased ex vivo T cell CD80 and CD86 expression (Figure 2A) reflects increased proliferation of CD80+/CD86+ T cell subsets, whereas increased ex vivo B cell CD80 expression in both HTLV-1 infected individuals and HAM/TSP patients (Figure 2B) is probably not mediated by increased proliferation of the CD80+ B cell subset. Here, CD80 is linked to tropical spastic paraparesis.