The IgG Subclasses of Red Cell Antibodies and Relationship to Monocyte Binding

Purified IgG₁, IgG₂, IgG₃, and IgG₄ myeloma proteins were coupled to red blood cells with chromic chloride either individually or in various combinations. Only red blood cells coated with IgG₁ or IgG₃ formed rosettes; red cells coated with IgG₃ appeared to predominate in this reaction. IgG₂, IgG₄, and IgA myeloma proteins coupled to red blood cells did not appear to inhibit the IgG₁ and/or IgG₃ also on the red cells from forming rosettes. The IgG subclass specificity of a number of red cell isoantibodies was determined. The majority were IgG₁ and IgG₃, as previously noted. IgG₂ was observed among some of these antibodies, namely in anti-D, anti-CD, anti-CDE, anti-s, and anti-Jk^a. Although rosette formation was strongly associated with the relative amounts of IgG₁ and IgG₃, particularly the latter, on red cells, a number of exceptions were noted.