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Antigen topography is critical for interaction of IgG2 anti‐red‐cell antibodies with Fcγ receptors
Author(s) -
KUMPEL BELINDA M.,
Van DeWINKEL JAN G. J.,
WESTERDAAL NOMDO A. C.,
HADLEY ANDREW G.,
DUGOUJON J. MICHEL,
BLANCHER ANTOINE
Publication year - 1996
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1046/j.1365-2141.1996.d01-1764.x
Subject(s) - antibody dependent cell mediated cytotoxicity , antibody , isotype , antigen , microbiology and biotechnology , subclass , monoclonal antibody , immunoglobulin g , receptor , fc receptor , biology , immune system , fragment crystallizable region , cytotoxicity , chemistry , in vitro , immunology , biochemistry
IgG antibodies to the Rh D polypeptide on red cells are normally IgG1 or IgG3, whereas antibodies produced in response to carbohydrate antigens such as the A and B blood groups are predominantly IgG2. The consequences of this isotype restriction for the immune destruction of red cells were investigated. Human IgG2 anti‐D and IgG2 anti‐A were isolated by affinity purification from an unusual anti‐D serum (DEL) and anti‐A sera, respectively. These antibodies were compared with IgG1 and IgG3 monoclonal anti‐D in in vitro functional assays of the interaction between IgG‐coated red cells (EA‐IgG) and cells bearing IgG Fc receptors (FcγR). Dimeric IgG2 anti‐D bound efficiently to cell lines transfected with FcγRIIa‐H131, an allotypic form of FcγRIIa which readily interacts with IgG2, IgG1 and IgG3. Unexpectedly, however, ‐D‐phenotype red cells coated with IgG2 anti‐D did not form rosettes with these cells, whereas EA‐IgG2 anti‐A and EA‐IgG1 and EA‐IgG3 anti‐D effectively formed rosettes with these transfectants at the same sensitization level (100 000 molecules IgG/red cell). In antibody‐dependent cell‐mediated cytotoxicity (ADCC) assays, lysis of EA‐IgG2 anti‐A was mediated via FcγRIIa, whereas lysis of EA‐IgG1 and EA‐IgG3 anti‐D was mediated via FcγRI or FcγRIII; EA‐IgG2 anti‐D was inactive in all functional assays. These experiments suggest that both IgG subclass and antigen structure affect functional IgG–FcγR interactions. The topography of the Rh D antigen, an integral membrane protein, ensures that anti‐D is bound near the lipid bilayer surrounded by the glycocalyx. This may sterically hinder access of FcγRIIa‐H131 to the FcγR recognition site on the relatively inflexible IgG2 anti‐D, but not to that of IgG1 or IgG3 anti‐D. In contrast, IgG2 bound to the A antigen on glycoproteins is not so constrained. The topography of the D and A antigens may thus determine whether functional interactions of red‐cell‐bound IgG2 anti‐D and IgG2 anti‐A with cells bearing Fcγ receptors can occur.