The low affinity IgE receptor CD23 may play a role in several B lympho
cyte functions, such as cell activation and multiplication, Ag present
ation, and IgE production. We have previously reported that ligation o
f the CD23 molecule with anti-CD23 mAb, or IgE-anti-IgE complexes, lea
ds to phosphoinositide hydrolysis and calcium mobilization through the
generation of Inositol (1,4,5) trisphosphate via a process involving
a Pertussis toxin insensitive GTP-binding protein. In our work, we sho
w that anti-CD23 mAb elicit an increase in cAMP concentration in human
peripheral blood-derived B lymphocytes. This effect was detected both
in resting and in IL-4-stimulated B cells displaying, respectively, l
ow and high levels of CD23. Maximum cAMP accumulation was reached abou
t 20 min after addition of the mAb. Involvement of FcgammaRII in this
process could be excluded because cAMP increase was also triggered by
mAb anti-CD23 F(ab')2 fragments. Accumulation of cAMP was also observe
d when IgE-sensitized activated B lymphocytes were challenged with the
specific hapten. Several lines of evidence indicate that the cAMP inc
rease after CD23 ligation may result, in part, from the stimulation of
phosphoinositidase C, inasmuch as it was markedly impaired by treatme
nt with TMB-8, an inhibitor of InsP3-induced calcium release from intr
acytoplasmic stores and with BAPTA, an intracellular calcium chelator.
Addition of GTP-gammaS to permeabilized B cells or to membrane prepar
ations did not potentiate the effect of the mAb, suggesting that a Gs
protein is not directly implicated in the generation of cAMP. Besides,
cAMP accumulation is not due to the production of PG because it is no
t modified by indomethacin, an inhibitor of the cyclooxygenase pathway
. Pretreatment of B lymphocytes with either anti-CD23 mAb or IL-4 led
to autologous as well as heterologous desensitization. This negative c
ross-talk, at the level of cAMP, between the signaling pathways trigge
red by ligation of CD23 and of the IL-4 receptor, could contribute to
the inhibitory effect of anti-CD23 mAb on IL-4-dependent B cell activa
tion and differentiation.