Eirikur Saeland,1
Jeanette H. W. Leusen,1 Gestur Vidarsson,1 Wietse Kuis,2
Elisabeth A. M. Sanders,2 Ingileif Jonsdottir,4 andJan G. J. van de Winkel1,3
Received 11 September
2002; accepted 31 December 2002; electronically published 12 May 2003.
Members of the leukocyteimmunoglobulin (Ig) G
receptor(FcR) family play akey role in antibody-mediatedphagocytosis and can
eitherenhance antigen presentation or
down-modulate immune responses. Westudied immune
responses toa pneumococcal conjugate (pneumococcalpolysaccharide serotype 1 [PPS1]tetanus
toxoid) and antibody-mediated protectionin mice
deficient forindividual FcRs and complementreceptor 3 (CR3). FcR chaindeficient (FcR chain-/-)
mice, which lackexpression of both FcRIand III, had significantlylower anti-PPS1 IgG2b
andIgG3 responses than didwild-type mice,
whereas FcRII-deficient(FcRII-/-)
mice had significantlyhigher IgG2a and IgG3
titers. Wild-type and FcRII-/-
mice were protected againstinfection with pneumococcal
serotype1, whereas immunized FcR chain-/- and FcRIII-deficientmice were not. ImmunizedCR3-deficient mice were
protectedagainst disease, and complement
depletion had little effecton protection. These dataindicate that activatory leukocyteFcR,
but not FcRII(a murine homologue ofhuman FcRIIb), contributes to
IgG-mediated protection against pneumococcaldisease.
Animal experiments were performedaccording to
institutional andnational guidelines.
Financial support: UniversityMedical Center Utrecht (WilhelminaKinderzickenhuisSTER grant); Netherlands Organizationfor
Scientific Research (grant901-07-229 to J.H.W.L.).
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