Inhibition by cholera toxin of rat polymorphonuclear leukocyte chemotaxis demonstrated in vitro and in vivo.

The effect of cholera toxin on the chemotaxis of rat polymorphonuclear leukocytes (PMN) was studied using a technique in which the movement of the cells towards a laser-lysed erythrocyte is followed under a phase-contrast microscrope. In vitro studies indicated that the intact toxin was capable of inhibiting PMN chemotaxis in a dose-dependent manner at doses ranging from 1 to 100 ng/ml. Subunits A and B of the toxin were without inhibitory activity when used alone, but after recombination their ability to inhibit chemotaxis was similar to that of the intact toxin, suggesting that the toxin is acting intracellularly. Cholera toxin has been reported to act in other systems via stimulation of adenyl cyclase with consequent elevation of intracellular cyclic adenosine 5'-monophosphate (cAMP) levels. It appears that this mechanism may also account for its ability to inhibit chemotaxis since there was a correlation, at all doses tested, between inhibition of chemotaxis and increased intracellular cAMP levels. Cholera toxin was also found to be active in vivo in that, after intrapleural injection of the toxin, the chemotaxis of cells subsequently recovered from the pleural cavity was markedly reduced. These results support previous findings which suggest that modification of leukocyte cAMP levels can influence the chemotactic responsiveness of these cells.