Elevated intracellular cyclic AMP is associated with the inhibition of
many inflammatory cellular responses. In this study, we examined the
effect of cyclic AMP on eosinophil chemotaxis. Eosinophils were isolat
ed from healthy human volunteers using an immunomagnetic method. Eosin
ophils were treated with agents that elevate intracellular cyclic AMP
and evaluated for chemotactic responses to platelet-activating factor
(PAF; 10(-6) M) and to complement factor 5a (C5a; 10(-8) M) in microch
emotaxis chambers. Forskolin, prostaglandin E(1) (PGE(1)), and a phosp
hodiesterase (PDE) IV-selective inhibitor inhibited eosinophil chemota
ctic responses. The mean per cent inhibition of eosinophil chemotaxis
in response to PAF by forskolin, PGE(1), and the PDE IV-selective inhi
bitor (10(-5) M) was 16.8 +/- 5.3, 26.6 +/- 9.5, and 35.1 +/- 6.1%, re
spectively (n = 5). The corresponding values for C5a were 17.5 +/- 7.9
, 20.8 +/- 10.7, and 39.5 +/- 5.0%. An exogenous cyclic AMP analogue (
dibutyryl cyclic AMP, 10(-3) M) also inhibited eosinophil chemotaxis b
y 69.4 +/- 12.8 and 66.9 +/- 11.6% in response to PAF and C5a, respect
ively (n = 5). We conclude that elevated intracellular cyclic AMP inhi
bits eosinophil chemotaxis.