The distribution of the gp40–45 Kd antigen bound by the WR17 monoclonal antibody of IgG2 subclass in normal lymphoid tissue was characterized by immunohistochemistry and immunofluorescence staining with flow cytometric analysis. The predominant staining pattern observed was characteristic of an anti‐pan‐B‐lymphocyte reagent. Weak reactions were observed by immunofluorescence staining of viable cell suspensions with all neutrophils and T‐lymphocytes in some normal donors. In tissue sections, B‐lymphocytes were stained and no cross reactions were observed with T‐lymphocytes, although macrophages stained in some sections.

A range of T‐ and B‐cell malignancies were stained with WR17 and the reactivity compared to that observed with other monoclonal antibodies in the CD 19, CD21 and CD22 clusters. All B‐non‐Hodgkin's lymphomas, B‐chronic lymphocytic, prolymphocytic and hairy cell leukaemia cells examined were stained by WR17 in indirect immunofluorescence assays, whilst the T‐cell tumours were negative. The same pattern was observed in cryostat sections of malignant tissue and in addition some tissue macrophages expressed the CD37 antigen cytoplasmically. Intra‐tumour heterogeneity of staining was observed with all the monoclonal antibodies tested, although overall WR17 consistently stained B‐cell tumours even when expression of the CD 19 pan‐B‐lymphocyte antigen could not be detected with some monoclonals.

Monoclonal antibodies, such as WR17, within the CD37 cluster and binding to the gp 40–45 Kd molecule, bind to mature B‐lymphocytes and identify the majority of B‐cell malignancies.