Figure 4.

CD28 costimulation drives expansion of human purified protein derivative (PPD)-specific T helper 1 cells in vitro. Carboxyfluorescein succinimidyl ester diacetate (CFSE) (5 µM) labeled peripheral blood mononuclear cells were cultured in the presence or absence of anti-CD3 monoclonal antibody (mAb) (HIT3a), PPD, tetanus and diphtheria toxoid, and Fab fragments of anti-CD28 mAb CD28.3 under Th0, Th1, or Th2 conditions for 6 days. (A) Representative FACS data of CFSE dilution and CD4 expression. (B) Frequencies of proliferated cells among CD4⁺ cells cultured under Th0 (left), Th1 (middle), or Th2 (right) culture conditions. Graphs show mean + SD from 19 donors assayed individually and tested with a one-tailed paired t-test (*p < 0.05, **p < 0.005, ****p < 0.0001).