Ia-like (HLA-DR) antigens in the diagnosis of lymphoma and undifferentiated tumors.

Several years of testing in clinical situations have shown that detection of Ia antigens by immunofluorescence is a highly reliable marker for human lymphomas, regardless of their histologic character and site. Ia antigens were found on malignant cells in patients with Hodgkin's disease (16/16), or with nodular (21/22) or diffuse (69/74) lymphomas. Four of the six Ia-negative lymphomas had T-cell markers. Expression of Ia antigens on lymphoma cells occurs in the absence of surface membrane immunoglobulin, IgG Fc, and complement receptors, which enables positive identification of aggressive "null"-cell lymphomas. Equally important, Ia antigens are absent in most solid tumors of epithelial (57/60) or connective tissue (11/11) origin, including "undifferentiated" tumors, thus facilitating their distinction from lymphoma.