Precision Medicine
Flow Cytometric Assays

Flow Cytometry


TBNK assay

TBNK assay is used to identify and quantitate T-cell, B-cell, and Natural Killer (NK) subsets. The TBNK assay provides valuable information about the composition of the immune system and is used in research and clinical scenarios to make informed decisions regarding patient care and treatment strategies.
  • T-cells originate in the thymus and are key components of the adaptive immune system [1-15]. Other sections of our website describe T-cell characteristics and the roles they play in cell-mediated immunity in more detail.

  • B-cells created in the bone marrow, are key players in the humoral immune response. B- cell development is a lengthy process of differentiation and maturation. Antigen recognition via the B-cell receptor, either directly or through presentation by an APC, ultimately results in their activation, maturation, immunoglobulin synthesis and immunological memory [19]. Similar to T-cells, B-cells also have a number of subsets, each specialised for their function. The principles behind most vaccinations are based on immunological memory preserved by B-cell subsets, plasma and memory B-cells [20].

  • NK-cells of the innate immune system originate in the bone marrow. The NK cell population constitute 5-20% of all circulating lymphocytes [21]. NK-cells are responsible for detecting and destroying infected and transformed cells. Unlike T-cells and B-cells, NK-cells do not recognize specific antigens. Instead, they use receptors to detect cells that lack self-antigens or express stress-induced molecules [22]. NK-cells utilise several cytolytic mechanisms e.g., death receptor ligation and degranulation, to lyse cells [21]. NKs can also initiate inflammation using pro-inflammatory cytokines. NK-cells do not exhibit immunological memory like T-cells and B-cells; their responses are rapid and largely non-specific.

The examples below highlight some of the key clinical uses of the TBNK assay:
  • Autoimmune and immunodeficiency disorders: The TNBK assay can help diagnose autoimmune and primary immunodeficiency disorders where there is an imbalance or deficiency in lymphocyte subsets.

  • Monitoring HIV/AIDS: The TNBK assay is used to monitor CD4+/CD8+ T-cell ratio in HIV-infected individuals to gauge the progression of the disease and the effectiveness of anti-retroviral therapy. A decrease in the CD4+/CD8+ ratio is indicative of immune system damage caused by the virus.

  • Lymphoma and Leukaemia: TBNK assays are used to identify abnormal lymphocyte to aid in diagnosis and monitoring of lymphomas and leukaemia.  

  • Transplant Medicine: TNBK assays are employed prior to organ transplant to monitor lymphocyte subsets and assess the risk of graft rejection.

  • Medical research: Researchers use TBNK assays to investigate immune responses to various diseases, vaccines, and therapies.

At PeploBio we perform the TBNK assay in technical harmonisation with leading providers of clinical flow cytometry services [23].
The TBNK assay can be used to identify T-cells, B-cells and NK-cells using the expression of the cell surface markers:
  • CD3+ in T-cells

  • CD3+CD4+ in T-helper cells

  • CD3+CD8+ in Cytotoxic T-cells

  • CD19+ in B-cells

  • CD3CD16+CD56+in NK cells

In our laboratories, we only use CE-IVD marked reagents and kits such as the BD Multitest 6-color (CD3 FITC / CD16 PE + CD56 PE / CD45 PerCP-Cy5.5 / CD4 PE-Cy7 / CD19 APC / CD8 APC-Cy7) TBNK kit with or without BD Trucount Tubes for absolute cell counts of lymphocyte subsets [24]. A less comprehensive assay using the 4-color BD Multitest TBNK assay containing CD3 FITC / CD16 PE + CD56 PE / CD45 PerCP / CD19 APC is also available [25]. These kits are especially designed for use with cutting edge flow cytometers such the BD FACS Lyric system we use in our laboratories. As mentioned in other sections of our website, the TBNK assay can be used clinically for the monitoring and diagnosis of a range of diseases including HIV/aids, autoimmune disease, immunodeficiency disorders, and lymphomas.

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[24] BD Bioscience; BD Multitest™ 6-Color TBNK; 2022 [cited Nov 2023]. Available from:
[25] BD Bioscience; BD Multitest ™ CD3/CD16+CD56/CD45/CD19; 2016 [cited Nov 2023]. Available from:

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