Demonstration of intrapleural immunoglobulin synthesis by agarose gel isoelectric focusing. A new specific method for the diagnosis of pleural effusions of inflammatory origin?

In order to demonstrate an intrapleural immunoglobulin (Ig) synthesis, pleural effusions and serum from 14 patients with pleural effusions of various causes (inflammatory condition, malignancies, primary lung cancers, pleural metastasis, and congestive heart failure) were investigated by agarose gel isoelectric focusing (AIEF), antiserum immunofixation with monospecific antiserum against IgG and IgA, and quantitative estimation of IgG and IgA. Intrapleural immunoglobulin synthesis was assumed to occur in patients with oligoclonal Ig limited to the pleural compartment or in patients with a raised IgG index, equal to (pleura/serum IgG):(pleura/serum albumin), or a raised IgA index, equal to (pleura/serum IgA):(pleura/serum albumin). Two of 3 patients with rheumatoid pleuritis had a polyclonal intrapleural immunoglobulin synthesis demonstrated by the presence of a raised IgG and IgA index without any signs of oligoclonal Ig production on AIEF. Two of 3 patients with assumed tuberculous pleuritis had, despite a normal IgG and IgA index, an oligoclonal intrapleural IgG production detected by AIEF. This oligoclonal reaction was shown by absorption studies with Mycobacterium tuberculosis antigen to be directed against M. tuberculosis. No signs of intrapleural immunoglobulin synthesis were found in the other 10 patients investigated.