Co-expression of T3 and surface immunoglobulin in neoplasms of 'early' B cells: a report of 2 cases.

Chronic lymphocytic leukaemia (CLL) and well-differentiated lymphocytic lymphoma (WDLL) characteristically express surface membrane immunoglobulin (SIg) and react with monoclonal antibodies (Mabs) directed against a marker present on most normal T cells, namely T1. These SIg-positive B cells are usually negative for other T cell markers including T3 (CD3) which is expressed in all normal T cells. We report 2 cases, 1 CLL and 1 WDLL, in which the peripheral lymphocytes not only expressed monotypic SIg but also reacted with the T3-specific Mabs UCHT1 and OKT3 by indirect immunofluorescence or immunoperoxidase staining. False-positive staining by both UCHT1 and OKT3 was excluded by showing that lymphocytes sensitized with an irrelevant mouse Mab did not stain with second layer antibodies and that lymphocytes stained with second layer antibodies alone were always completely unreactive. Also, in 1 case the determinants demonstrated by both anti-Ig and UCHT1 were re-expressed after capping and shedding, i.e. appeared to be endogenous. The B cell origin of the CLL lymphocytes was supported by the finding of CK gene rearrangement in the absence of T beta gene rearrangement. It seems therefore that neoplasms of 'early' B cells may show bidirectional differentiation and co-express markers that are believed to be T-specific.