title: Discordant expression of immunoglobulin and its associated molecule mb-1/CD79a is frequently found in mediastinal large B cell lymphomas.
abstract: Mediastinal large B cell lymphomas are uncommon neoplasms that are thought to originate from thymic B cells. An unusual feature of these neoplasms is that they often lack surface immunoglobulin (Ig), a molecule ubiquitously expressed by most mature B cells. In the present study we have analyzed 12 cases of mediastinal large B cell lymphoma for the expression of the mb-1/CD79a polypeptide. This is a component, together with B29/CD79b, of a heterodimer that is associated with surface Ig on normal B cells. Our aim was to see whether loss of Ig in this type of lymphoma is associated with loss of the accompanying CD79a molecule. We have also evaluated 128 B cell lymphomas of other categories to see whether any of them show discordance between mb-1 and Ig expression and analyzed 30 T cell lymphomas as Ig-negative controls. We found that 5 of the 7 mediastinal large B cell lymphomas with interpretable staining results for both mb-1 and Ig, lack Ig but expressed CD79a (mb-1). This phenotype was very rare in other categories of B cell lymphoma, being found among 110 cases in only 5 cases that were all follicular lymphoma. The remaining 105 B cell lymphomas displayed mb-1+/Ig+ phenotype. All 30 T cell lymphomas were mb-1 negative. We conclude that discordant mb-1/Ig expression occurs commonly in mediastinal large B cell lymphomas. In addition, the finding that 11 of 12 of these neoplasms express a phenotype (CD10-, CD19+, CD20+, CD21-, CD22+, CD23-/+) that is very similar to that described for thymic medullary B cells reinforces the idea that most mediastinal large B cell lymphomas are of thymic B cell origin. The correlation between mb-1 and Ig staining patterns in B cell lymphomas of other categories reveals that in the majority (90%), expression of the antigen receptor complex parallels that of mature B cells. These data therefore confirm that the expression of the mb-1 protein provides independent strong evidence for the B lineage of lymphomas and may be used for their routine phenotypic characterization.
authors.affiliation: Department of Pathology, Henri Mondor Hospital, Créteil, France.
authors.forename: P
authors.initials: P
authors.lastname: Kanavaros
authors.forename: P
authors.initials: P
authors.lastname: Gaulard
authors.forename: F
authors.initials: F
authors.lastname: Charlotte
authors.forename: N
authors.initials: N
authors.lastname: Martin
authors.forename: C
authors.initials: C
authors.lastname: Ducos
authors.forename: M
authors.initials: M
authors.lastname: Lebezu
authors.forename: D Y
authors.initials: DY
authors.lastname: Mason
mesh_terms: D015703:Antigens, CD; D051925:CD79 Antigens; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D016130:Immunophenotyping; D008221:Lymphoid Tissue / Q000378:metabolism; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D016403:Lymphoma, Large B-Cell, Diffuse / Q000378:metabolism*; D016399:Lymphoma, T-Cell / Q000378:metabolism; D008479:Mediastinal Neoplasms / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D051925:CD79 Antigens; C497881:CD79A protein, human; D007136:Immunoglobulins; D008562:Membrane Glycoproteins; D011947:Receptors, Antigen, B-Cell