Fc Receptors for IgE on Normal Rat Lymphocytes

Abstract

The binding of IgE to Lewis rat lymphocytes was investigated by employing a rosette assay consisting of aldehyde-fixed ox erythrocytes to which a rat IgE myeloma protein had been adsorbed. The lymphocytes were also analyzed for rosette formation with fixed erythrocytes coated with normal rat IgG and ox erythrocytes sensitized with rabbit IgG antibodies. Surface immunoglobulin-positive cells (sIg⁺) were detected with fixed ox erythrocytes coated with goat F(ab′)₂ anti-rat light chain antibodies.

The highest number of IgE-binding lymphocytes were found in the spleen (18.7%), followed by peripheral blood (13.3%), bone marrow (12.3%), Peyer's patches (5.5%), lymph nodes (4.1%), and thoracic duct (0.0%). Depletion and mixed rosette experiments with different indicator cells showed that most of the IgE-binding cells belonged to the sIg⁺ cells and were presumably B cells. They did not form rosettes with normal rat IgG-coated indicator cells but formed rosettes with the rabbit IgG antibody-sensitized cells. The IgE binding was inhibited by rat IgE Fc fragments but not Fab fragments. Reduction and alkylation in aqueous solution and heating at 56° for 4 hr of IgE myeloma protein or its Fc fragment abolished its reactivity with lymphocytes. A weak cross-inhibition with both homologous and heterologous IgG and human IgE was observed, however, only at protein concentrations of 5 to 10 mg/ml. Brief treatment of the lymphocytes with trypsin abolished the binding of rat IgE and IgG, whereas it had little effect on the rosette formation with rabbit IgG-coated cells.

These findings indicate that a relatively large population of rat B lymphocytes, which have either few or low affinity Fc receptors for rat IgG, have Fc receptors for IgE.