Immunoenzymatic typing of lymphoplasmacytoid skin infiltrates

Monoclonal immunoglobulin-producing lymphomas (immunocytomas, plasmacytomas, and immunoblastomas) constitute 15 to 20% of all cutaneous lymphomas. Their differentiation from polymorphous lymphoplasmacytoid inflammatory or pseudolymphomatous infiltrates may be difficult if sections are stained for a single light chain only. It was the aim of the study to elucidate the ratio of the kappa- to lambda-positive cells in 10 lymphoproliferative, 5 pseudolymphomatous, and 42 inflammatory lymphoplasmacytoid cutaneous infiltrates and to characterize them by the type of Ig (alpha, gamma, mu, kappa, or lambda) synthesized intracellularly. An indirect immunoenzymatic double-labeling method (alkaline phosphatase and peroxidase) was used for the simultaneous demonstration of kappa and lambda light chains and alpha, gamma, and mu heavy chains in paraffin sections. Ig-producing lymphomas of the skin show patchy monoclonal proliferations of cells synthesizing kappa IgM in almost 50% of the cases (5 of 10). Monoclonality is claimed if the ratio of lambda- to kappa-positive cells is at least 1:10, or vice versa. In polyclonal inflammatory and pseudolymphomatous infiltrates, the lambda/kappa ratio never exceeds 1:5. The most common cell type found in these reactive infiltrates produces gamma heavy chain; some produce alpha chain, but only a few produce mu chain. In high-grade malignant lymphomas, the tumor cells may lose their capacity for Ig production.