Most Ig receptors exist as multi-subunit complexes with a unique ligan
d binding alpha chain and a common signaling FcR gamma-chain, The myel
oid Fc gamma RIIa (CD32) appears unique among FcR because both ligand-
binding and signaling capacity are found in the cu chain. Within the c
ytoplasmic tails of Fc gamma RIIa and FcR gamma-chain similar, but not
identical, activatory motifs (ITAMs) have been defined, in which tyro
sines play an important role. Previously, Fc gamma RIIa-ITAM was shown
to be critical for both proximal and distal activatory functions in I
IA1.6 B-cell transfectants. Triggering of interleukin-2 (IL-2) release
and antigen presentation was absent in Fc gamma RIIa, but not in FcR
gamma-chain receptor complexes, We now assessed the capacity of Fc gam
ma RIIa wild-type and Fc gamma RIIa/gamma chimeric molecules to trigge
r IL-2 production and antigen presentation by B cells, Both of these f
unctions could solely be triggered by receptors containing the FcR gam
ma-chain ITAM, but not the Fc gamma RIIa-ITAM. In addition, Fc gamma R
IIa was capable of functional interaction with FcR gamma-chain, thus r
econstituting the capacity to trigger IL-2 release and antigen present
ation, These data document qualitative differences between Fc receptor
ITAMs. (C) 1995 by The American Society of Hematology.