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Beta-2 Microglobulin
Related Subjects: |Major Histocompatibility complex |Immune response |Complement |Opsonisation |Toll-like Receptors (TLRs) |Immunoglobulins |Immunology |Antigen presenting cells |T lymphocytes |Beta-2 Microglobulin
🔎 What is Beta-2 Microglobulin (B2M)?
- Beta-2 Microglobulin (B2M) is a low molecular weight protein (<12 kDa) found on the surface of all nucleated cells.
- It is the light chain component of MHC Class I molecules, essential for their stability and antigen presentation to CD8+ T cells.
- B2M is shed into the blood as cells turn over and is normally filtered by the glomeruli and reabsorbed in the proximal tubules.
🧬 Physiology
- Produced by all nucleated cells; levels reflect cellular turnover + immune activation.
- Maintains structural integrity of MHC-I, ensuring proper antigen presentation.
- Excreted almost entirely by the kidneys → sensitive to changes in renal function.
📖 Clinical Relevance
B2M is a useful biomarker for renal function, haematological malignancy prognosis, and immune activation.
📈 Causes of Elevated B2M
- Renal disease: CKD, AKI, tubular disorders → reduced clearance.
- Hematologic malignancies: Multiple Myeloma (part of ISS staging), lymphoma, leukaemia.
- Immune activation: Autoimmune (RA, SLE), chronic infection.
- HIV infection: Reflects ongoing immune activation; correlates with disease progression.
- Dialysis-related amyloidosis: Long-term dialysis → B2M amyloid deposits in joints/tendons.
🩺 Diagnostic & Prognostic Uses
- Renal function: Sensitive marker of tubular dysfunction; rises early in AKI.
- Oncology: Strong prognostic factor in Multiple Myeloma — higher B2M = worse survival (used in ISS staging).
- Immune monitoring: Tracks disease activity in HIV, autoimmune diseases, chronic infections.
📊 Normal vs Abnormal
- Normal range: ~1.0–2.5 mg/L (serum).
- High levels: >3 mg/L suggest pathology (renal impairment, immune activation, malignancy).
💡 Clinical Pearls
- In CKD, elevated B2M reflects reduced clearance rather than increased production.
- In multiple myeloma, both tumour burden and renal impairment elevate B2M → explains its prognostic power.
- Mnemonic (KIM-HIV): Kidney disease • Immune activation • Malignancy • HIV.
🌟 Summary
B2M is an MHC-I component and marker of cell turnover. It rises in renal failure, immune activation, and malignancy. It is especially important as a prognostic biomarker in multiple myeloma and in assessing immune system activity in chronic diseases.
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