Mapping the functional topography of Fc gamma with monoclonal antibodies: localization of epitopes interacting with the binding sites of Fc receptor on human K cells.
A panel of monoclonal antibodies (mAb) specific for the C gamma 2, C gamma 3 or inter C gamma 2/C gamma 3 domain epitopes was tested for inhibition of antibody-dependent cellular cytotoxicity (ADCC) specific for anti-D IgG-coated erythrocytes. Significant inhibition of ADCC was demonstrable for some antibodies having specificity for C gamma 2 or C gamma 3 domain epitopes, while others gave no inhibition. Fab fragments of a representative C gamma 2-specific antibody (A55) and C gamma 3-specific antibody (x3a8) retained their inhibitory capacity in lymphocyte-mediated ADCC, but only A55 Fab inhibited monocyte-mediated lysis. Furthermore, the Fab portion of A55 completely abolished the complement-dependent enhancement of ADCC mediated by concanavalin A-stimulated cells, while x3a8 Fab had no effect in this system. On the other hand, x3a8 Fab inhibited the binding of anti-D IgG-sensitized erythrocytes to lymphocytes while A55 Fab did not influence this latter interaction. The results suggest that C gamma 2 domain-FcR interaction is essential for the triggering of lytic process both in lymphocyte and in monocyte-mediated ADCC, while C gamma 3 domain has no role in the latter but is responsible for the appropriate contact between effector lymphocytes and target cells. A site in the region of Lys274 appears to be critical for triggering of both lymphocyte and monocyte-mediated ADCC.
G
G
Sármay
R
R
Jefferis
E
E
Klein
M
M
Benczur
J
J
Gergely
D000911:Antibodies, Monoclonal / Q000276:immunology*; D000920:Antibody-Dependent Cell Cytotoxicity; D001665:Binding Sites; D003167:Complement Activation; D000939:Epitopes; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007141:Immunoglobulin Fc Fragments / Q000276:immunology* / Q000378:metabolism; D007128:Immunoglobulin Fragments / Q000276:immunology*; D007694:Killer Cells, Natural / Q000276:immunology*; D008214:Lymphocytes / Q000276:immunology; D009000:Monocytes / Q000276:immunology; D011487:Protein Conformation; D011961:Receptors, Fc / Q000276:immunology* / Q000378:metabolism; D017452:Receptors, IgG; D012397:Rosette Formation
D000911:Antibodies, Monoclonal; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007128:Immunoglobulin Fragments; D011961:Receptors, Fc; D017452:Receptors, IgG