pax-5

The pax-5 gene is essential for B-cell differentiation. There are at least four isoforms, of which pax-5a has been most studied. Pax-5  encodes the 50 kDa B-cell specific activator protein, BSAP. Pax-5 is expressed by pro-, pre- and mature B cells, but is downregulated during terminal differentiation of plasma cells. Pax-5 influences the expression of other B-cell specific genes, including CD19 and CD20 and CD79a, preceding the expression of CD20. Pax-5 is silenced at the plasma cell stage under the influence of B-lymphocyte-induced maturation protein-1 (PRDM1)5.

Pax-5 is expressed during mouse embryogenesis within the developing brain in a way that is temporarily and spatially tightly condoled. Pax-5 deficient mice show deformation of the mid-brain. Expression in human embryogenesis occurs in the mesoencephalon and spinal cord6.

Antibodies are reactive in formalin-fixed paraffin-embedded tissue. Immunoreactivity is nuclear.

Immunohistochemical expression

 

pax-5

CD 20

 

pre-B ALL / B-cell lymphoblastic lymphoma

20/201, 3/32, 1/23

7/201

CLL/SLL

38/381, 13/133, 2/24

38/381

lymphoplasmacytic lymphoma

8/81, 5/52, 1/23

8/81

splenic marginal zone lymphoma

4/41

4/41

hairy cell leukaemia

12/121

12/121

plasma cell myeloma

2/391, 0/23

3/391

CD20-positive myeloma

18/255

 

MGUS

0/21

0/21

solitary plasmacytoma of bone

0/11

0/11

extraosseus plasmacytoma

0/11, 0/42, 0/33

0/11

heavy-chain disease

1/21

0/21

mucosa associated lymphoid tissue lymphoma

14/141, 5/52, 7/123

14/141

nodal marginal zone lymphoma

2/21, 2/24

2/21

follicular lymphoma

64/641, 3/32, 20/213, 2/24

64/641

mantle cell lymphoma

26/261, 3/32, 21/213, 2/24

26/261

diffuse large B-cell lymphoma

95/991, 6/62, 19/243, 9/104

93/991

TCRBCL

4/44

 

mediastinal (thymic) large B-cell lymphoma

2/21

2/21

intravascular large B-cell lymphoma

2/21

2/21

pleural effusion lymphoma

1/11

1/11

Burkitt lymphoma

5/51, 1/12, 1/2

5/51

Classical Hodgkin lymphoma

112/1171, 28/312, 5/143, 27/294

25/1171, 8/282

lymphocyte predominance Hodgkin lymphoma

58/581, 10/102, 2/43, 15/154

58/581

peripheral T-cell lymphoma

0/151, 0/202, 0/123, 0/174

0/151

anaplastic large cell lymphoma

0/111, 0/192, 0/83, 0/74

0/111

T-cell ALL / lymphoblastic

0/201, 0/22, 0/33

0/201

 

 

 

PU.1

BSAP

Oct-2

 
 

Nodular lymphocyte predominance Hodgkin lymphoma

15/151

15/151

15/151

 

Classical Hodgkin lymphoma

2/351

27/291

0/291

CLL/SLL

6/61

2/21

3/31

FL

7/71

2/21

4/41

MCL

2/31

2/21

4/61

MZL

3/31

2/21

2/21

DLBCL

11/181

9/101

15/171

TCRBCL

0/61

4/41

4/41

B-cell non-Hodgkin lymphoma

29/431

21/221

32/361

myeloma

negative1

 

 

PTCL

0/171

0/171

 

ALCL

0/71

0/71

 

 

 

Merkel cell carcinoma

29/316

 

Small cell carcinoma

22/306

Carcinoid tumour

0/176

PNET/Ewing's sarcoma

0/36

Neuroblastoma

0/26

   

 

 

Diagnostic utility

Identification of B-cell lymphomas including:

 

References

1 Torlakovic, E., G. Torlakovic, et al. “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 2002; 26(10): 1343-50. with clarificatrions kindly provided by Dr Torlakovic.

2 Foss, H. D., R. Reusch, et al. (1999). “Frequent expression of the B-cell-specific activator protein in Reed- Sternberg cells of classical Hodgkin's disease provides further evidence for its B-cell origin.” Blood 94(9): 3108-13.

3 Krenacs, L., A. W. Himmelmann, et al. (1998). “Transcription factor B-cell-specific activator protein (BSAP) is differentially expressed in B cells and in subsets of B-cell lymphomas.” Blood 92(4): 1308-16.

4 Torlakovic, E., A. Tierens, et al. (2001). “The transcription factor PU.1, necessary for B-cell development is expressed in lymphocyte predominance, but not classical Hodgkin's disease.” Am J Pathol 159(5): 1807-14.

5 Lin, P., M. Mahdavy, et al. (2004). "Expression of PAX5 in CD20-positive multiple myeloma assessed by immunohistochemistry and oligonucleotide microarray." Mod Pathol 17(10): 1217-22.

6 Dong HY, Liu W, Cohen P, et al. B-cell specific activation protein encoded by the PAX-5 gene is commonly expressed in merkel cell carcinoma and small cell carcinomas. Am J Surg Pathol 2005; 29:687-92

7 Kozmik Z, Sure U, Ruedi D, et al. Deregulated expression of PAX5 in medulloblastoma. Proc Natl Acad Sci U S A 1995; 92:5709-13

This page last revised 18.8.2005.

©SMUHT/PW Bishop