CD 79a

Dako (JCB117, HM57) and Immunotech (HM47).

This antibody is applicable to paraffin-embedded tissue sections. Heat pretreatment in citrate buffer is necessary for antigen retrieval to improve staining pattern. CD 79a may also be applied to acetone-fixed cryostat sections and fixed-cell smears.

Membrane-bound immunoglobulin (mIg) on human B lymphocytes is non-covalently associated with a disulfide-linked heterodimer, which consists of two phosphoproteins of 47 kD and 37 kD, encoded by the mb-1 and B29 genes respectively (Mason et al, 1991; Van Noesel et al, 1991). Association of IgM with the mb-1 protein is necessary for membrane expression of the B-cell antigen receptor complex. When antigen is bound to this B-cell complex, a signal transduction is transmitted to the interior of the cell, accompanied by phosphorylation of several components following induction of tyrosine kinase activity. The mb-1/B29 dimer seems to be analogous to the association of the T-cell receptor with the CD 3 components (Homback et al, 1990).
Studies have shown that mb-1 is present throughout B-cell differentiation and is B-cell specific (Mason et al, 1991). Its high degree of specificity is probably a reflection of its crucial role in signal transduction after antigen binding to the B-cell antigen receptor complex. Themb-1 and B29 proteins were designated CD 79a and CD 79b at the Fifth International Workshop on Human Leukocyte Differentiation Antigens (Boston 1993). JCB117 was raised against the recombinant protein containing part of the extracellular portion of the CD 79a (mb-1) polypeptide (Mason et al, 1995). Clone HM57 was raised against a synthetic peptide sequence comprising amino acids 202-216 ofmb-1 protein (Sakaguchi et al, 1988). This oligopeptide represents the intracytoplasmic C-terminal part of themb-1 protein.

The mb-1 (CD 79a) chain appears before the pre-B cell stage and is still present at the plasma cell stage. JCB117 reacts with human B cells in paraffin-embedded tissue sections, including decalcified bone marrow trephines. When applied to 454 paraffin-embedded tissue biopsies, it reacted with the majority (97%) of B-cell neoplasms. This covered the full range of B-cell maturation including 10/20 cases of myeloma/plasmacytoma. This antibody also labeled precursor B-cell acute lymphoblastic leukemia, making it the most reliable B-cell marker detectable on paraffin-embedded specimens (Mason et al, 1995). T-cell and non-lymphoid neoplasms were negative, indicating that JCB117 may be of value in the identification of B-cell neoplasms.
The mb-1 protein has also been detected in nodular lymphocyte-predominant Hodgkin's disease using monoclonal antibody JCB117; however, only 20% of non-lymphocyte-predominant cases expressed mb-1.A rare phenotypic characterization has been demonstrated in mediastinal large B-cell lymphomas, with the majority being mb-1+/ Ig-(Kanavaros et al, 1995).

We have found JCB117 to be superior to HM57, the latter demonstrating cross-reactivity with smooth muscle in paraffin sections.

•Homback J, Tsubata T, Leclercq L, Stappert H, Reth M 1990 Molecular components of B cell antigen receptor complex of IgM class. Nature 343: 760-762.

•Kanavaros P, Gaulard P, Charlotte F et al 1995 Discordant expression of immunoglobulin and its associated molecule mb-1/CD 79a is frequently found in mediastinal large B cell lymphomas. American Journal of Pathology 146: 735-741.

•Mason DY, Cordell JL, Tse AGD et al 1991 The IgM associated protein mb-1 as a marker of normal and neoplastic B cells. Journal of Immunology 147: 2474-2482.

•Mason DY, Cordell JL, Brown MH et al 1995 CD 79a: a novel marker for B cell neoplasms in routinely processed tissue samples. Blood 86: 1453-1459.

•Sakaguchi N, Kashiwamura S, Kimoto M, Thalmann P, Melchers F 1988 B lymphocyte lineage restricted expression of mb-1, a gene with CD3-like structural properties. EMBO Journal 7: 3457-3464.

•Van Noesel CJM, Van Lier RAW, Cordell JL et al 1991 The membrane IgM-associated heterodimer on human B cells is a newly defined B cell antigen that contains the protein product of the mb-1 gene. Journal of Immunology 146: 3881-3888.

Manual of diagnostic antibodies for immunohistology / Anthony S.-Y. Leong, Kumarasen Cooper, F. Joel W.-M. Leong.