PAX5

PAX5

A gene on chromosome 9p13, of which there are multiple isoforms, of which PAX-5A is most studied. It encodes 50-kD B-cell specific activator protein (BSAP), which is expressed in pre-B and mature B cells, but is downregulated/silenced during terminal differentiation of plasma cells under the influence of B-lymphocyte-induced maturation protein-1 (PRDM1). PAX-5A influences the expression of other B-cell specific genes, including CD19 and CD20 and CD79a, preceding the expression of CD20.
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As reviewed by Ibrahim and colleagues, distinct genetic rearrangement, amplification, and somatic hypermutation involving point mutations of the immunoglobulin (Ig) variable region are associated with BCL6, BCL2, p53, and PAX5 genes in PTLD.
The large, atypical lymphocytes are positive for PAX5, OCT2, MUM1, CD30, and EBER, and negative for CD10 and BCL-6.
Immunohistochemistry demonstrated large lymphocytes representing CD20 positive B-cells which were partially positive for PAX5, CD45, and Bcl-6 and negative for CD3, CD5, CD10, CD15, CD 30, CD 34, CD 43, and Bcl 2.
Four micron thick sections were cut from paraffin blocks of the terminal ileum and stained with hematoxylin and eosin (H&E) and immunostains for CD20, CD3, CD30, CD15, CD45, CD21, EMA, BCL6, OCT2, PAX5, IgD, PD-1, and kappa and lambda immunoglobulin light chains.
Loss of T-cell antigen expression and aberrant expression of CD15 and PAX5 is noted in a subset of cases.
Immunohistochemistry revealed that the malignant cells, including the very large atypical cells, were immunoreactive for CD45, CD20 (Figure 2(a)), CD79a, PAX5 (Figure 2(b)), BCL6 (Figure 2(c)), and MUM1 (predominantly in the larger cells, Figure 2(d)) and were negative for CD3, CD5, CD10 (Figure 2(e)), CD30 (Figure 2(f)), CD15 (Figure 2(g)), LMP1, EBER (Figure 2(h)), and CMV.
PAX5 protein, another transcription factor encoded by a gene in the Pax family, also known as B-cell specific activation protein (BSAP), has been demonstrated to be crucial for B-cell commitment and function [16].
Acute myeloid leukemia with t(8;21) often expresses the B-cell markers CD19, CD79a, and PAX5, which is associated with transcriptional upregulation of the PAX5 gene.
Immunohistochemistry was positive for CD20 and PAX5 but negative for CD10 and BCL-1 and flow cytometry revealed a large monoclonal kappa-restricted B-cell population of 38% that was negative for CD5 and CD10.
Apart from CD5, SLL is typically positive for other B-cell antigens, such as CD19, CD20, CD22, CD23, CD79a, PAX5, and surface light-chain immunoglobulins.
By immunohistochemistry (IHC), the lymphoid cells were positive for PAX5, BCL-2 (more than 50%), cMYC, and Tdt immunostains (Figures 4(a)-4(d)) with high mitotic index reflected by strong KI-67 positivity (Figure 4(e)).
Immunohistochemical expression of PAX5 and TdT by Merkel cell carcinoma and pulmonary small cell carcinoma: a potential diagnostic pitfall but useful discriminatory marker.