IRF4

IRF4 Full Name

interferon regulatory factor 4

IRF4 Introduction

Interferon Regulatory Factor 4 (IRF4), also widely known in diagnostic pathology as Multiple Myeloma Oncogene 1 (MUM1), is a pivotal transcription factor belonging to the IRF family. Unlike most other IRF family members that are ubiquitously expressed and primarily orchestrate innate antiviral interferon responses, IRF4 expression is tightly restricted to the hematopoietic compartment, specifically within lymphoid and myeloid lineages. Physiologically, IRF4 is indispensable for the development, activation, and terminal differentiation of immune cells. In the B-cell lineage, it is the master regulator that drives the exit of B cells from the germinal center, orchestrating class switch recombination (CSR) and driving their terminal differentiation into antibody-secreting plasma cells. In the T-cell compartment, IRF4 is strictly required for the differentiation of various helper T-cell subsets, including Th2, Th9, Th17, and regulatory T cells (Tregs).

Figure 1. BATF forms a heterodimer with IRF4. (Source: Fujisawa S, et al. 2025)

The clinical notoriety of IRF4 is deeply rooted in hematological malignancies, where it frequently acts as a potent oncogene. It is considered a hallmark diagnostic marker and a critical survival factor in Multiple Myeloma (MM). In fact, myeloma cells are highly dependent on IRF4 for their survival and proliferation, a phenomenon notoriously described as "IRF4 addiction." Beyond myeloma, IRF4/MUM1 is a critical biomarker used to classify and diagnose Diffuse Large B-Cell Lymphoma (DLBCL). Specifically, strong expression of IRF4 is a defining feature of the Activated B-Cell (ABC) subtype of DLBCL, which generally carries a poorer prognosis compared to the Germinal Center B-cell (GCB) subtype. Furthermore, chromosomal translocations involving the IRF4 gene locus (such as t(6;14)) are recurrently found in certain large B-cell lymphomas, directly driving tumorigenesis by placing the gene under the control of active immunoglobulin enhancers.

Alternate Names for IRF4

IRF4; interferon regulatory factor 4; MUM1; LSIRF; NF-EM5; multiple myeloma oncogene 1; lymphocyte-specific interferon regulatory factor;

• 1. Fujisawa S, et al. The transcription factor BATF pioneers the differentiation program of effector CD8+ T cells through the interaction with IRF4. Cell Rep. 2025 Aug 26;44(8):116129.
  2. Nam S, et al. Essential role of interferon regulatory factor 4 (IRF4) in immune cell development. Arch Pharm Res. 2016 Nov;39(11):1548-1555.