Oh. Brekke et al., HUMAN-IGG ISOTYPE-SPECIFIC AMINO-ACID-RESIDUES AFFECTING COMPLEMENT-MEDIATED CELL-LYSIS AND PHAGOCYTOSIS, European Journal of Immunology, 24(10), 1994, pp. 2542-2547
In this report we describe the construction of anti-5-iodo-4-hydrooxy-
3-nitrophen-acetyl (NIP) mouse/human immunoglobulin (Ig)G4 chimeric mo
lecules with altered amino acid residues in the C(H)2 domain. Three mu
tants are described: Gln-268 is substituted by His in gamma 4 Q268H, S
er-331 is substituted by Pro in gamma 4 S331P, and in gamma 4 Q268H/S3
31P both residues are substituted. The ability of the mutant molecules
to induce complement-mediated cell lysis (CML) and phagocytosis by Fc
gamma RII- and Fc gamma RIII-bearing polymorphonuclear leukocytes (PM
N) were measured. In CML, gamma 4 Q268H was inactive, but both gamma 4
S331P and gamma 4 Q268H/S331P were active provided that the antigenic
density on the target cells was high. In phagocytosis mediated by PMN
, the mutants gamma 4 S331P and gamma 4 Q268H/S331P were both active o
nly when complement was introduced. gamma 4 Q268H was not active in ph
agocytosis under any conditions. We conclude that His-268 in human IgG
molecules does not modulate CML activity or phagocytosis mediated by
Fc gamma RII and/or Fc gamma RIII. Pro-331 rescues CML activity in IgG
4 molecules when the epitope density on the target cells is high, but
does not affect Fc gamma RII/Fc gamma RIII-mediated phagocytosis. In t
his manner the mutants gamma 4 S331P and gamma 4 Q268H/S331P mimic hum
an IgG2. This could indicate a structural similarity between IgG2 and
these mutant molecules that distinguish them from both IgG1 and IgG3.