Neonates develop vigorous Th1 and Th2 primary responses to NIMA-like alloantigens. Neonates and adults were injected with allogeneic cells, as described for Figure 2. Seven days later, purified CD4⁺ cells from injected neonates or adults were stimulated with allogeneic APCs and assayed for cytokine production by ELISA after 48 hours (A-C) or frequency of cytokine-producing cells by ELISPOT after 72 hours (D-F) as described in “Culture conditions for cytokine ELISA and ELISPOT.” The in vitro responses of age-matched, naive controls, determined in parallel were as follows: for neonates: IFNγ, 109 (± 145) ng/mL and 1598 (± 534) secretors/10⁶ cells; IL-4, 0.17 (± 0.03) ng/mL and 3798 (± 1412) secretors/10⁶ cells; for adults: IFNγ, 9.4 (± 5.6) ng/mL and 1760 (± 339) secretors/10⁶ cells; IL-4, 0.024 (± 0.024) ng/mL and 2054 (± 91) secretors/10⁶ cells. Error bars represent the mean (± SD) of data from 2 independent experiments. Statistical significance was determined using a 2-tailed t test; **P = .002