CD79a

Membrane-bound immunoglobulin is associated with a heterodimer of mb-1 (CD79a) and B29 (CD79b) proteins. The antibody JCB117 is superior to HM57 in its specificity for CD79a; the latter shows cross-reactivity with smooth muscle.

Antibodies are effective on paraffin-embedded tissue1.

Immunohistochemical expression

• B lymphocytes from before the pre-B stage to mature plasma cells. Since CD79a is downregulated in terminal differentiation, the continuing immunoreactivity may be due to cross-reaction with CD79b2.

• 97% of B cell lymphomas. Positivity for CD79a may persist after anti-CD20 therapy has abolished positivity for CD20

• precursor B-cell ALL: positivity may occur in the absence of other B-cell markers.

• rarely in T-ALL/T-LBL While the CD79a (mb-1) promoter is regulated by Pax-5, this gene is in addition at least partly regulated by PU.1, another important B-cell transcription factor. However, this transcription factor is expressed in a subset of T-acute lymphoblastic leukemias2.

• The Reed-Sternberg cell of lymphocyte predominant Hodgkin's disease

• some plasmacytomas

• some cases of t(15;17) acute promyelocytic leukaemia and of AML.

Diagnostic utility

References

1 Leong A S-Y, Cooper K and Leong FJ W-M. Manual of diagnostic antibodies for immunohistology. 2nd edition, 2003

2 Torlakovic, E., G. Torlakovic, et al. (2002). “The value of anti-pax-5 immunostaining in routinely fixed and paraffin- embedded sections: a novel pan pre-B and B-cell marker.” Am J Surg Pathol 26(10): 1343-50.

3 Arber DA, Jenkins KA,Slovak ML CD79 alpha expression in acute myeloid leukemia. High frequency of expression in acute promyelocytic leukemia. Am J Pathol 1996; 149:1105-10

©SMUHT/PW Bishop