Differential Binding of IgG Subclasses to Enzyme‐treated Human Lymphocytes

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Abstract
Human erythrocytes coated with each of the 4 human IgG subclasses were used to detect Fc.gamma. receptors on human peripheral blood lymphocytes (HPBL). Rosette formation was obtained only with erythrocytes coated with IgG3 (EA.gamma.3). Neuraminidase treatment of HPBL induced rosette formation with EA.gamma.1, EA.gamma.2, and EA.gamma.4 complexes. Pronase treatment also induced rosette formation to a lesser extent, but abolished EA.gamma.3 rosetting. Trypsin treatment enhanced EA.gamma.3 rosette formation. These phenomena occurred on T and non-T lymphocytes. Erythrocytes coated with small quantities of IgG3 did not form rosettes with HPBL. Neuraminidase treatment enhanced their binding; pronase did not. These 2 phenomena occurred only on non-T lymphocytes. Rosette formation with EA.gamma.1 was also obtained with lymphocytes stimulated in vitro with mitogens. After 2 days of culture, stimulated lymphocytes expressed receptors that were able to bind EA.gamma.1 and EA.gamma.3 complexes. The existence of cryptic receptors for IgG1, IgG2 and IgG4 that could be disclosed by neuraminidase and pronase treatment and exposed on stimulated lymphocytes was suggested. A hypothesis of 1 or several Fc.gamma. receptors was suggested.
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