Immunohistochemical staining of non-Hodgkin's lymphoma in paraffin sections using the MB1 and MT1 monoclonal antibodies

We have performed a single blind trial to assess the value of the monoclonal antibodies MB1 and MT1 in lymphoma classification. Sixty cases of non‐Hodgkin's lymphoma (NHL) were stained with MB1 and MT1 using an indirect immunoperoxidase technique in paraffin sections. The majority of B tumours (27/33) stained with MB1, and most of the T tumours (24/27) stained with MT1. The MB1 antibody often produced rather weak staining but it was apparently highly specific for B cells, with only three (3/27) of the T tumours (two cases of ‘malignant histiocytosis’ of the intestine (MHI) and one pleomorphic T‐cell lymphoma) displaying ‘false’ positivity. The MT1 antibody generally produced very strong staining, but it was not very selective, with 14/33 of the B lymphomas displaying ‘false’ positivity. The cross‐reactivity observed in 17 cases led to only three misdiagnoses, two B tumours being designated as T lymphomas and one T tumour being designated as a B lymphoma. In a few cases (7/17), dual staining with both antibodies precluded firm diagnosis. In other cases (6/17), classification was possible despite some of the tumour cells showing dual staining. The seventeenth case was a plasmacytoma displaying MT1 positivity only. While the monoclonal antibodies MB1 and MT1 are of use in classifying lymphomas in paraffin section, they are not entirely lineage‐specific, and the uncritical use of these two reagents alone may give rise to misdiagnosis; the use of a panel of monoclonal antibodies may yield more accurate results. As with any immunohistochemical marker, their limitations should be recognized; interpretation must be judicious and always in the context of the histological appearances.