ANTIGEN VALENCY AS A DETERMINANT OF THE RESPONSIVENESS OF IGE-SENSITIZED RAT BASOPHIL LEUKEMIA-CELLS

Rat basophil leukemia (RBL) cells were sensitised with varying proport ions of monoclonal IgE anti-ovalbumin (OVA) and anti-DNP antibodies, a nd serotonin release was measured after challenge with aggregated OVA or dinitrophenylated human serum albumin (DNP-HSA). Highly aggregated OVA was shown to provoke the degranulation of RBL cells that had been sensitised with an IgE preparation containing 2% IgE anti-OVA antibodi es. Highly substituted DNP32-HSA induced degranulation of RBL cells se nsitised with just 0.5% antigen-specific IgE. When cells were sensitis ed with high percentages of specific IgE, maximum degranulation was se en at concentrations of 2 mu g/ml (aggregated OVA) and 50 ng/ml (DNP-H SA), while moderate degranulation was still seen at antigen concentrat ions as low as 50 and 2 ng/ml, respectively. Low-molecular weight aggr egates of OVA and low-valency DNP4-HSA only stimulated degranulation w hen high percentages of RBL Fee receptor were occupied by antigen-spec ific IgE. The sensitising abilities of two anti-DNP monoclonal antibod ies of differing affinities were compared. When challenged with low-va lency antigen, only cells sensitised with the higher-affinity monoclon al antibody exhibited moderate levels of degranulation. Degranulation required exposure to high antigen challenge doses (5 mu g/ml). Cells s ensitised with either monoclonal antibody responded strongly when chal lenged with a wide range of concentrations (1-250 ng/ml) of high-valen cy DNP32-HSA, although greater sensitivity was always seen with the hi gher-affinity antibody. These results suggest that antigen valency is a critical parameter for mast cell function, and that low-affinity ant ibody may be capable of sensitising mast cells to high-valency antigen .