Monoclonal antibody to human eosinophils recognizing 95 kD surface membrane antigen

Autoreactive eosinophils associated with spontaneous autocytotoxicity in bronchial asthma

Allergic autocytotoxicity (ACT) assay is extensively investigated as an in vitro equivalent of oral ingestion challenge with food antigens among patients with food hypersensitivity. In direct ACT, food antigenic determinants interact directly with plasma cell membranes of sensitive individuals. Antibody-dependent ACT is also known as antibody-dependent-cell-mediated-cytotoxicity (ADCC) phenomenon, when food antigens combine with specific antibody through cell membranes Fc receptors among normal and sensitive individuals. Spontaneous ACT is a separate mechanism of white blood cells disintegration which does not require in vitro priming of the cells, neither by antigen or antibody. Spontaneous ACT occurs in some individuals as "background noise" in addition to direct and antibody-dependent ACT. The exact cellular nature of ACT phenomena are unknown at the present time with the exception that the common identifying factor for each of them is the disintegration and death of human white blood cells. Electron microscopy studies among four bronchial asthma patients with spontaneous ACT demonstrated eosinophils with atypical crystalloid cores and diffuse autolytic pattern of granular membranes. These ultrastructural characteristics are associated with new functional profiles of eosinophils expressed morphologically as natural killer and/or suicidal potency. At least two subpopulations of eosinophils are mediating ACT. The first subpopulation has normal ultrastructure observed in direct ACT and the second subpopulations has altered morphology of eosinophils granules described in spontaneous ACT. The natural killer-suicidal eosinophils presented in patient with spontaneous ACT illustrate a new pathway of cytodestructive mechanism in anaphylactic injury.

Functional study of a monoclonal antibody to IgE Fc receptor (Fc epsilon R2) of eosinophils, platelets, and macrophages

An IgM mAb (BB10) was produced by immunization of mice with human eosinophils purified according to their abnormal low density ("hypodense" cells), and previously shown to exhibit increased IgE-dependent antiparasite cytotoxicity. This BB10 antibody, selected for positive fluorescence staining of hypodense blood or lung eosinophils and low or negative staining of normodense eosinophils or neutrophils, could strongly inhibit IgE-dependent cytotoxicity of human eosinophils and platelets. The specificity for the IgE Fc receptor was suggested by the high levels of inhibition of IgE rosettes formed by eosinophils after incubation with the purified IgM fraction of BB10, whereas other receptors (Fc gamma R, CR1) were not affected. On the other hand, BB10, able to inhibit rat eosinophil Fc epsilon R, did not react with the IgE Fc receptor on mast cells or basophils. A technique using radioiodinated BB10 allowed us to quantify the specific binding of BB10 to human eosinophils and platelets. Competition experiments revealed a crossinhibition between the binding of BB10 and IgE, suggesting the specificity of BB10 for the IgE binding site of eosinophil, platelet, and monocyte Fc epsilon R. Three proteins having extrapolated Mr of 32,000, 43,000-45,000, and 97,000 were found in the platelet extract eluted from a BB10 or from an IgE immunosorbent column. These findings confirm the similarities between IgE Fc receptors on human eosinophils, platelets, and macrophages, already observed with polyclonal antibodies directed against the B lymphocyte Fc epsilon receptor. They suggest, moreover, that the mAb BB10 can represent a good reagent for further investigations on the structure and the functions of this IgE Fc receptor (Fc epsilon R2).