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A new look at lymphoma immunohistology.

READERS of pathology journals today may sometimes feel like the critic who complained that the biography he had just read told him more about its subject than he wished to know. For an increasing proportion of the histopathologic literature seems to be devoted to immunocytochemical studies of antigen expression in different types ofhuman neoplasms. Nowhere is this diet richer than in the field of human lymphoma, a reflection ofthe fact that more monoclonal antibodies have been raised against white cells than against any other human cell type. More than a thousand such reagents were submitted to last year's Third International Workshop on Human Leucocyte Differentiation Antigens. Analysis of these antibodies in the Workshop made it possible to expand the list of white-cell-associated molecules classified according to the CD system from 26 (clusters of differentiation recognized at the Second Workshop in 1984) to 45and this list does not include several biochemically characterized leukocyte antigens which were only recognized by single antibodies (and hence failed to meet one of the major criteria for CD classification). Monoclonal antibodies against many of these molecules are available from several commercial sources, as are a variety ofexcellent reagents for immunoenzymatic labeling of tissue sections, with the consequence that any histopathologist with a few hundred dollars and a pair oftechnically trained hands to spare can investigate antigen expression in different types of human lymphoma. The ease with which such studies can be performed and the interest they have aroused among histopathologists are attested to by the large number of published articles on this subject. At the beginning of a thought-provoking review, published in this issue of the Journal, Picker and his colleagues' from Stanford suggest (although it is not the main theme of their paper) that most of these studies have been concerned with topics that are of limited relevance to the real problems that occur in lymphoma pathology thus implying that the forest of immunocytochemical lymphoma literature may be loud with the sound ofpathologists barking up the wrong trees! What are the topics to which other investigators in this field have been devoting their attention? Picker and his colleagues mention two major themes: 1) Comparison of cell phenotype with morphologic classification 2) Attempts to find the cell of origin of various lymphoid malignancies, and to fit this cell into schemes of normal lymphoid differentiation