Differential binding of IgG subclasses to enzyme-treated human lymphocytes

Area of Science:

• Immunology
• Cell Biology

Background:

• Fc gamma receptors (FcγRs) on lymphocytes play a crucial role in immune responses.
• Understanding the expression and function of different IgG subclass receptors is essential for comprehending immune regulation.

Purpose of the Study:

• To investigate the presence and characteristics of Fc gamma receptors for human IgG subclasses on human peripheral blood lymphocytes (HPBL).
• To explore the influence of enzymatic treatments on Fc gamma receptor expression and binding affinity.

Main Methods:

• Human erythrocytes were coated with specific human IgG subclasses.
• Rosette formation assays were performed using HPBL and coated erythrocytes.
• HPBL were treated with neuraminidase, pronase, or trypsin to assess effects on Fc gamma receptor binding.
• Lymphocytes were stimulated in vitro with mitogens to evaluate Fc gamma receptor expression on activated cells.

Main Results:

• Direct rosette formation was observed only with erythrocytes coated with IgG3 (EAγ3).
• Neuraminidase treatment of HPBL induced rosette formation with EAγ1, EAγ2, and EAγ4.
• Pronase treatment also induced rosetting but abolished EAγ3 binding, while trypsin enhanced EAγ3 rosetting.
• Enzyme treatments revealed Fc gamma receptors on both T and non-T lymphocytes, with distinct effects observed on non-T cells for low-affinity IgG3 binding.
• Stimulated lymphocytes expressed receptors binding both EAγ1 and EAγ3.

Conclusions:

• The study suggests the existence of cryptic Fc gamma receptors for IgG1, IgG2, and IgG4 on human lymphocytes.
• These receptors can be unmasked by enzymatic treatments like neuraminidase and pronase.
• Fc gamma receptor expression is altered upon lymphocyte activation, with stimulated cells binding IgG1 and IgG3.
• The findings support a hypothesis of one or more Fc gamma receptors with varying affinities and regulatory mechanisms.