Jaw1/LRMP, a germinal centre‐associated marker for the immunohistological study of B‐cell lymphomas

Abstract Jaw1, also known as lymphoid‐restricted membrane protein (LRMP), is an endoplasmic reticulum‐associated protein. High levels of Jaw1/LRMP mRNA have been found in germinal centre B‐cells and in diffuse large B‐cell lymphomas of ‘germinal centre’ subtype. This paper documents Jaw1/LRMP expression at the protein level in human tissues by immunohistochemical and western blotting analysis using an antibody reactive with paraffin‐embedded tissues. Jaw1/LRMP was highly expressed in germinal centre B‐cells (in keeping with gene expression data), in ‘monocytoid B‐cells’, and in splenic marginal zone B‐cells. It was absent, or present at only low levels, in mature T‐cells, although cortical thymocytes were weakly positive. Among lymphoid neoplasms, Jaw1/LRMP was found in germinal centre‐derived lymphomas (follicle centre lymphoma, Burkitt's lymphoma, lymphocyte‐predominant Hodgkin's disease) but not in T‐cell neoplasms (with the exception of a single T lymphoblastic lymphoma). Classical Hodgkin's disease and myeloma lacked Jaw1/LRMP but many cases of chronic lymphocytic leukaemia (but not mantle zone lymphoma) were Jaw1/LRMP‐positive. Approximately half of the marginal zone lymphomas were Jaw1/LRMP‐positive. In diffuse large B‐cell lymphomas, Jaw1/LRMP was found in three‐quarters (24/32) of the cases classified phenotypically as being of ‘germinal centre’ type, but it was also expressed in almost half (13/28) of the ‘non‐germinal centre’ cases. A similar proportion of ‘non‐germinal centre’ cases were positive for the protein products of two other genes expressed highly in germinal centre cells (HGAL/GCET2 and PAG). The fact that all three of these proteins are expressed in a significant proportion of diffuse large B‐cell lymphomas assigned to the ‘non‐germinal centre’ category indicates that the immunophenotypic categorization of diffuse large B‐cell lymphoma according to cellular origin may be more complicated than currently understood. Finally, the expression of Jaw1/LRMP in other types of lymphoma and in non‐lymphoid tissues/tumours may be of interest in differential diagnosis and research. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.