Human rTNF-alpha (greater than or equal to U/ml) decreased PMN nondirected and directed migration to FMLP to approximately 50% of control.
Adenosine (100 microM) almost completely restored hrTNF-inhibited migration (nondirected from 54 to 92% and directed migration to from 54 to 93% of control). The lowest concentration of
adenosine that restored hrTNF-inhibited migration was 3 microM, and the
adenosine analogue, 5'-(N-cyclopropyl)-carboxamido-adenosine (
CPCA) was more potent than
adenosine. Although
CPCA binds to A2-receptors and stimulates
adenylate cyclase, the reversal of hrTNF-inhibited chemotaxis was found to be independent of both PMN cAMP content and binding to A2-receptors, because neither 8-Br-cAMP nor
pertussis adenylate cyclase restored hrTNF-inhibited PMN chemotaxis and the A2-receptor antagonist,
1,3-dipropyl-7-methylxanthine decreased
CPCA stimulated cAMP but enhanced
CPCA-restoration of hrTNF-inhibited chemotaxis. The effect of
adenosine could be augmented by inhibition of
adenosine uptake and decreased by
adenosine deamination.
Pentoxifylline, (3,7 dimethyl-1-[5 oxo-hexyl]
xanthine), like
adenosine also restored PMN chemotaxis inhibited by hrTNF. The
adenosine receptor antagonist, 1,3-dipropyl-8(phenyl-p-acrylate)-xanthine (
BW A1433U), decreased restoration of hrTNF-inhibited chemotaxis by
CPCA or
pentoxifylline. Thus, the inhibitory effect of hrTNF on PMN migration can be counteracted by
adenosine,
CPCA,
pentoxifylline, and compounds that increase
adenosine availability to the surface of the PMN. Inasmuch as an A1-selective agonist
N6-cyclopentyladenosine was less active, and the action of the A2-selective agonist
CPCA was enhanced by an A2-receptor antagonist, we hypothesize that neither A1 or A2 receptors are involved in
adenosine restoration of hrTNF-inhibited chemotaxis. Further, increased cAMP, an A2-regulated event, does not cause the effect, and
adenosine restoration of hrTNF-inhibited migration does not appear to be mediated by changes in PMN [
F-actin],
FMLP receptor expression, or cytosolic
calcium. Hence, the restoration of hrTNF-inhibited chemotaxis is controlled by a novel
cyclic AMP-independent action on the PMN surface.