Cyclic GMP and Lectin-Induced Lymphocyte Activation

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Abstract
Purified human peripheral lymphocytes incubated with the mitogenic plant lectins phytohemagglutinin and concanavalin A were examined for alterations in intracellular cGMP and cAMP under a variety of experimental conditions and using multiple techniques for the isolation and purification of cGMP and cAMP before assay of the cyclic nucleotides by radioimmunoassay. In contrast to work reported by others, we have been unable to demonstrate consistent increases in cGMP under any of the experimental conditions used and with any of the various purification schemes. In these same experiments exogenous cGMP added to the lymphocytes could be measured, and the immunoreactive material was destroyed by cyclic nucleotide phosphodiesterase, indicating that our inability to measure increases in cGMP was not caused by our inability to measure cGMP. Under identical experimental conditions, small but consistent and statistically significant increases in cAMP were noted. In addition, other parameters of lymphocyte activation, 45Ca uptake (an early parameter), and incorporation of 3H thymidine into DNA were unimpaired. These data call to question the concept of cGMP as the second messenger in lectin-stimulated human peripheral lymphocytes.

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