Acidic pH increases intracellular cAMP, which is a critical signaling molecule in eosinophil viability. Eosinophils were isolated from mouse spleen or human peripheral blood; eosinophils were incubated in media of over a pH range (A-B) for 30 minutes in the presence of IBMX, and accumulated intracellular cAMP was measured via an ELISA from eosinophil lysates. n = 3 mice per group. Results shown as the mean intracellular cAMP ± SD. Representative experiments (of 3) are shown. Murine eosinophils were incubated in IBMX (a phosphodiesterase inhibitor) or an adenylate cyclase inhibitor (C) for 4 hours. Human eosinophils were exposed to various concentrations of adenylate cyclase inhibitor SQ22536 and IBMX at pH 7.5 and pH 6.0 for 24 hours. Human eosinophil viability was assessed (D), and intracellular cAMP was measured from the lysates of a sample of each well (taken at 10-minute time point); (E) demonstrates human eosinophil viability as a function of intracellular cAMP. Viability analysis was performed using annexin V and 7AAD. Results show the average ± SD (of triplicate incubations). *P < .05.