Pj. Daffern et al., C3A IS A CHEMOTAXIN FOR HUMAN EOSINOPHILS BUT NOT FOR NEUTROPHILS .1.C3A STIMULATION OF NEUTROPHILS IS SECONDARY TO EOSINOPHIL ACTIVATION, The Journal of experimental medicine, 181(6), 1995, pp. 2119-2127
Inflammatory action of the potent chemotaxin C5a has been well charact
erized on a variety of human cell types, including neutrophils, monocy
tes, basophils, and eosinophils. The cellular effects of C3a are less
well defined. Contradictory reports have been published for C3a activa
tion of neutrophils. Recent reports that C3a activates both basophils
and eosinophils prompted us to reinvestigate the effects of C3a stimul
ation on eosinophils. We hypothesized that C3a activation of eosinophi
ls, cells that are present in most neutrophil preparations, might lead
to neutrophil activation. Using neutrophils of 98% purity, we observe
d no evidence of cellular activation after stimulation with either C3a
, recombinant human C3a (rhC3a), or the synthetic C3a analogue C3a 57-
77, Y57. Eosinophils purified to >98% purity displayed concentration-d
ependent polarization, chemotaxis, and enzyme release by stimulation w
ith C3a, rhC3a, and the synthetic C3a analogue. An inactive form of C3
a, C3a(desArg), failed to stimulate either eosinophils or neutrophils.
Using neutrophil preparations containing 5-9% eosinophils, up to 20%
of neutrophils became polarized after exposure to C3a. Likewise, we de
monstrated that supernatant from C3a-stimulated eosinophils promotes n
eutrophil chemotaxis. Eosinophil polarization experiments were repeate
d in the presence of antibody to the C5a receptor (C5aR) to show that
C3a and C5a interact with different receptors. C3a activates eosinophi
ls in the presence of anti-C5aR antibody at concentrations that fully
block C5a activation. We conclude that eosinophils are directly activa
ted by tither C3a or C5a, whereas C3a failed to activate neutrophils.
C3a acts on eosinophils via a receptor that is distinct from C5aR. Sin
ce neutrophils are indirectly stimulated by C3a, eosinophils contamina
ting neutrophil preparations may explain earlier reports that C3a acti
vates human neutrophils.