Treatment with IL-2 cplxs prevents alloantibody production humoral response and impairs memory cell differentiation. (A) Sera of mice were collected ∼2 wk post skin-graft rejection and analyzed for the presence of donor graft-specific IgG (naïve B6 n = 5; PBS control n = 11; 3 d cplx = 5; 3 d cplx/rapa n = 10; 30 d LD cplx/rapa n = 5; 30 d LD cplx/rapa + a–IL-6 n = 4). (B) Sera of naïve, cplx-treated or PBS-treated control mice were analyzed for donor-specific IgG early after skin grafting (day 10, day 20; n = 3–5 per group). (C) Rejection of a second BALB/c graft applied without additional treatment ∼2 wk after rejection of the first graft (naïve first: n = 11, MST = 8 d; naïve second n = 4, MST = 5 d, P < 0.0001 vs. naïve first; cplx second: n = 4, MST = 10.5 d, P = 0.0058 vs. naïve second; P = 0.1383 vs. naïve first; log-rank test). (D) Sera of mice were analyzed for the presence of anti-donor IgG after the first and second rejection (n = 2–4 per group). Groups were compared with a 2-tailed t test with unequal variances.