TLR-2 is a biomolecule, which plays a role in the human immune system. TLR-2 is a membrane protein, a receptor, which is expressed on the surface of certain cells and recognizes native or foreign substances, and passes on appropriate signals to the cell and/or the nervous system.

TLR-2 is a member of a large family of homologous Toll-like receptors (TLRs). TLR2 has also been designated as CD282 (cluster of differentiation 282).

Impact

TLR-2 is a membrane receptor found at the surface of immune system cells that recognises many bacterial, fungal, viral and endogenous substances. Phagocytosis of bound materials takes place in endosome/phagosome and a cellular activation, so that the elements of the innate immune system take over such as macrophages, PMN and dendritic cells tasks of the nonspecific immune defense, B1a and form MZB first anti-bodies and uses in the process the specific anti-body formation. Here cytokine is involved e.g. Tumor necrosis factor-alpha (TNF α) and different interleukins (IL-1alpha, IL-1beta, IL-6, IL-8, IL-12). Before TLRs were discovered, some of the materials specified below were grouped under the term so-called "Moduline". By that rather T_h1 appropriate cytokine pattern is seen in most experimental models an immune deviation this way, away of the T_h2-expression. Conjugates are developed as vaccines or already used without a priori knowledge.

One only 2006 recognized characteristic is the expression of the TLR-2 on the Tregs (special form of the T-cells), which is brought equally to TCR determined proliferation and functional inactivity. Thereby, a disinhibition of the early inflammation phase and the specific anti-body formation is reached. After reduction of the exciter number many exciter-specific Tregs are present, which, now without TLR-2-Signal, become active and the specific like the inflammatory immune reaction to restrain (see also TGF beta, Interleukin 10). Older literature, which attributes a direct immune stimulation effect over TLR-2 to a given substance, must be interpreted under circumstances that the used TLR-2-knockouts has regularly quite few Tregs.

Functionally relevant polymorphism is described, which reduced to a function restriction and thus usually survival rate with infections/sepsis with Gram-positive bacteria leads in particular.

The signal transduction is represented in the article toll-like receptor.

Expression

TLR-2 is expressed on microglia, Schwann cells, monocytes, macrophages, dendritic cells, polymorphonuclear leukocytes, B-cells (B1a, MZB, B2), T-cells including regulatory T cells (CD4, CD25). TLR-2 is likewise in the epithelium of the bronchial tube and the alveoli.

Agonists

Agonist	Organism
Lipoteichoic acid	Gram-positive bacteria
Peptidoglycan	Gram-negative and Gram-positive bacteria
atypical LPS	Leptospirosis and Porphyromonas gingivalis
MALP-2 and MALP-404 (lipoproteins)	Mycoplasma
-	Chlamydophila pneumoniae
OspA	Borrelia burgdorferi (Lyme disease)
Porin	Haemophilus influenzae
Antigen mixtures	Propionibacterium acnes
LcrV	Yersinia
Lipomannan	Mycobacterium: Mycobacterium tuberculosis
GPI anchor	Trypanosoma cruzi
Lysophosphatidylserine	Schistosoma mansoni
Lipophosphoglycan (LPG)	Leishmania major
Glycophosphatidylinositol (GPI)	Plasmodium falciparum
Zymosan	Saccharomyces cerevisiae
-	Malassezia (commensal yeast)
Antigen mixtures	Aspergillus fumigatus, Candida albicans
hsp60, as peptide transporter and adjuvant for antigen presentation	-
-	Herpes simplex virus
-	Varicella zoster virus
-	Cytomegalovirus (CMV)
Hemagglutinin	Measles

Further reading