Figure 2. Lymphocyte proliferative responses to the mitogens phytohemagglutinin (A), pokeweed mitogen (B), and Concanavalin A (C) after systemic saline, morphine, and/or naltrexone. The proliferative responses to all three mitogens after systemic morphine differed significantly from systemic saline, naltrexone, and morphine + naltrexone (P < 0.001). Naltrexone significantly increased the response to pokeweed mitogen (B; P < 0.05).