Determination of immunoglobulin class by pattern of absorption to protein A-sepharose coupled with immunoglobulin class specific antibodies.

The pattern of absorption of the different major immunoglobulin classes by protein A and protein A coupled with antibody to human IgA or IgM has been evaluated as a simple means of identifying the class of a particular immunoglobulin in small volumes of human serum. Rabbit anti-IgA or anti-IgM coupled with protein A-Sepharose gel effectively removed IgA or IgM respectively from human serum in addition to the subclasses of IgG removed by protein A alone. The manner in which an immunoglobulin-related property is removed from human serum by protein A and its conjugates with specific antibodies can thus serve as an index of the class of that particular immunoglobulin.