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Event Title

T-cells, Activation/Proliferation
Short name: T-cells, Activation/Proliferation

Key Event Overview

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AOPs Including This Key Event

AOP Name Event Type Essentiality
Covalent Protein binding leading to Skin Sensitisation KE Strong

Taxonomic Applicability

Name Scientific Name Evidence Links
human Homo sapiens Strong NCBI
mouse Mus musculus Strong NCBI

Level of Biological Organization

Biological Organization

How this Key Event works

T-cells are typically affected by protein-hapten complexes presented by dendritic cells on Major Histocompatibility Complex (MHC) molecules. Molecular understanding of this process has improved in recent years (see[1]). Briefly, MHC molecules are membrane proteins which present the small peptide antigens placed in a “groove” of the MHC molecule during its intracellular synthesis and transport to the cell surface. In the context of the MHC molecular on the cell surface, the small peptide antigen is recognized via the T-cell receptors as self or non-self (e.g. foreign). If this peptide is a foreign peptide, such as part of a protein-hapten complex, the T-cell will be activated to form a memory T-cell, which subsequently proliferates. If reactivated upon presentation by skin dendritic cells, these memory T-cells will induce allergic contact dermatitis[2].

How it is Measured or Detected

Methods that have been previously reviewed and approved by a recognized authority should be included in the Overview section above. All other methods, including those well established in the published literature, should be described here. Consider the following criteria when describing each method: 1. Is the assay fit for purpose? 2. Is the assay directly or indirectly (i.e. a surrogate) related to a key event relevant to the final adverse effect in question? 3. Is the assay repeatable? 4. Is the assay reproducible?

Most protocols recognize the importance of the process of antigen-presentation, so in vitro T-cell-based assays are typically co-cultures of allergen-treated dendritic cells and modified T-lymphocytes with expression of selected biomarkers (e.g. interferon gamma), or T-cell proliferation being the reported outcome. Much of this work has been reviewed by Martin et al[1]. It should be remembered that lymph node cell proliferation is the basis for the in vivo mouse Local Lymph Node Assay (LLNA). OECD TG 429 is the validated test guideline for the Skin Sensitisation: Local Lymph Node Assay[3] together with its two non-radioactive modifications (LLNA-DA TG442A[4] and LLNA-BrdU ELISA TG 442B[5]).

Overview table: How it is measured or detected

Method(s) Reference URL Regulatory


Validated Non


Local Lymph Node Assay (LLNA) TG 429 [1] X X
TG 442A LLNA:DA [2]
TG 442B LLNA: BrdU-ELISA [3]

Evidence Supporting Taxonomic Applicability

Some in vitro assays have been developed using human T cells[1]. Lymph node proliferation is the basis for the in vivo mouse LLNA.


  1. 1.0 1.1 1.2 Martin SF, Esser PR, Schmucker S, Dietz L, Naisbitt DJ, Park BK, Vocanson M, Nicolas JF, Keller M, Pichler WJ, Peiser M, Luch A, Wanner R, Maggi E, Cavani A, Rustemeyer T, Richter A, Thierse HJ, Sallusto F. 2010. T-cell recognition of chemical, protein allergens and drugs; toward the development of in vitro assays. Cell. Mol. Life Sci. 67: 4171-4184.
  2. Vocanson M, Hennino A, Rozieres A, Poyet G, Nicolas JF. 2009. Effector and regulatory mechanisms in allergic contact dermatitis. Allergy 64: 1699-1714.
  3. OECD 2010. Test No.429: Skin sensitization: Local Lymph Node Assay. OECD Guidelines for the Testing of Chemicals, Section 4: Health effects. OECD Publishing. Doi: 10.1787/9789264071100-en.
  4. OECD 2010. Test No442A: Skin sensitization: Local Lymph Node Assay:DA. OECD Guidelines for the Testing of Chemicals, Section 4: Health effects. OECD Publishing. Doi: 10.1787/9789264090972-en.
  5. OECD 2010. Test No.442B: Skin sensitization: Local Lymph Node Assay: BrdU-ELISA. OECD Guidelines for the Testing of Chemicals, Section 4: Health effects. OECD Publishing. Doi: 10.1787/9789264090996-en.