Lymphoplasmacytoid lymphoma: an immunohistological study

Eighteen cases of lymphoplasmacytoid lymphoma (LPL) have been immunophenotypically characterized with a panel of 26 monoclonal antibodies. All cases expressed leucocyte common antigen, class II MHC and stained with B cell markers (CD19, CD20, CD22) although a variable proportion of tumour cells were noticed to have lost some B cell marker expression. There was some phenotypic heterogeneity with variable immunostaining with KB61, CD21, and CD5. A variable proportion of cells in all cases contained cytoplasmic immunoglobulin. Surface immunoglobulin light chain restriction was demonstrated in 11 cases and heavy chain predominance in 16 cases. Few tumour cells were proliferating as indicated by Ki67 immunostaining. A wide variation in number of macrophages and T lymphocytes were present in association with the tumours. A significant association between the expression of CD5 and the presence of peripheral blood lymphocytosis was noticed (p less than 0.003) but there was no association between CD5 and co-expression of IgM and IgD. This data supports an origin from non-germinal centre cells for LPL and suggests that CD5 expression by B cells may be related to lymphocyte migration. LPL shows some immunological heterogeneity and can present diagnostic difficulties, but its poor prognosis makes it an important category of lymphoma to recognise.