CD4 and thrombotic thrombocytopenic purpura: For the whole MM patient cohort, regardless of CD4+ T cell subtypes, a weak positive association of CTLA-4 level on CD4+ T cells with TTP was indicated (p = 0.053) (Figure 3a); however, this relationship was found to be strengthened only with regards to the Teff subset (p = 0.02) (Figure 3b), and CTLA-4 expression on Treg was not associated with TTP.