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1. Receptors and Signaling
Dr. Mukhtar, Family Physician, Associate Dean

2. Contents
• B-Cell Receptors
• T-Cell Receptors

3. Introduction
• In biochemistry and pharmacology, receptors are
chemical structures, composed of protein, that
receive and transduce signals that may be
integrated into biological systems.

4. T-cell receptor
• The T-cell receptor (TCR) is a molecule found on
the surface of T cells, or T lymphocytes, that is
responsible for recognizing fragments of antigen.

5. • The TCR is composed of two different protein
chains (that is, it is a heterodimer).
• In humans 95% of T cells the TCR consists of an
alpha (α) chain and a beta (β) chain, whereas in
5% of T cells the TCR consists of gamma and
delta.

6. Structural characteristics of the TCR
• The TCR is a disulfide-linked membrane-anchored
heterodimeric protein normally consisting of the highly
variable alpha (α) and beta (β) chains.
• T cells expressing this receptor are referred to as α:β (or
αβ) T cells, though a minority of T cells express an
alternate receptor, formed by variable gamma (γ) and
delta (δ) chains, referred as γδ T cells.

7. • Each chain is composed of two extracellular domains:
Variable (V) region and a Constant (C) region.
• The Constant region is proximal to the cell membrane,
followed by a transmembrane region and a short
cytoplasmic tail, while the Variable region binds to the
peptide/MHC complex.

9. The TCR complex
• The TCR receptor complex is an octomeric
complex of variable TCR receptor α and β chains
with three signalling molecules CD3δ/ε, CD3γ/ε
and ζζ.

10. • Since the cytoplasmic tail of the TCR is extremely
short, making it unlikely to participate in
signaling, these signaling molecules are vital in
propagating the signal from the triggered TCR
into the cell.

12. TCR co-receptors
• The signal from the T-cell complex is enhanced
by simultaneous binding of the MHC molecules by
a specific co-receptor.
• On helper T cells and regulatory T cells, this co-
receptor is CD4 that is specific for MHC class II.
• On cytotoxic T cells, this co-receptor is CD8 that
is specific for MHC class I.