S. Wernersson et al., IgG-mediated enhancement of antibody responses is low in Fc receptor gammachain-deficient mice and increased in Fc gamma RII-deficient mice, J IMMUNOL, 163(2), 1999, pp. 618-622
Immunization with IgG/Ag or IgE/Ag complexes leads to a higher production o
f specific Abs than immunization with Ag alone. The enhancing effect of IgE
is exclusively dependent upon the low-affinity receptor for IgE, Fc epsilo
n RII, whereas the mechanism behind IgG-mediated enhancement is unknown. We
have investigated whether receptors for the Fc part of IgG are required fo
r responses to IgG/Ag, Mice lacking the gamma subunit of Fc receptors (FcRs
) (FcR gamma(-/-)), Fc gamma RII. (Fc gamma RII-/-), or Fc gamma RIII (Fc g
amma RIII-/-) were immunized with BSA-2,4,6-trinitrophenyl (TNP) alone or B
SA-TNP complexed to monoclonal TNP-specific IgG1, IgG2a, or IgG2b, As expec
ted, all subclasses enhanced the Ah-response to BSA in wild-type mice, Enha
ncement was in the same order of magnitude in Fc gamma RIII-/- mice (less t
han or equal to 177-fold of controls administered Ag alone), whereas it was
abrogated in FcR gamma(-/-) mice and augmented in Fc gamma RII-/- mice (le
ss than or equal to 5147-fold of controls). The response to IgE/Ag complexe
s in FcR gamma(-/-) and Fc gamma RII-/- mice was similar to that seen for w
ild-type mice, demonstrating that non-Fc gamma R-dependent responses were n
ormal, Our observations suggest that IgG/Ag complexes enhance Ab responses
via Fc gamma Rs, Moreover, they reveal a strong negative regulation of Ab r
esponses to IgG/Ag exerted by Fc gamma RII.