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CD81

CD81, also known as TAPA-1 (tetraspanin-1), is a member of the tetraspanin family of small cell surface glycoproteins. It is widely expressed, with high levels on B cells, hepatocytes, and various epithelial and endothelial cells, and it contributes to the organization of membrane microdomains that coordinate signaling and adhesion events.

The protein contains four transmembrane domains, short extracellular N- and C-termini, and two extracellular loops, EC1

Functionally, CD81 acts as a co-receptor in B cell receptor signaling, partnering with CD19 and CD21 to

CD81 has important roles in host-pathogen interactions. It is best known as a critical entry factor for

In clinical and research contexts, CD81 serves as a valuable cell surface marker for identifying B cells

and
EC2.
The
EC2
loop
is
larger
and
contains
conserved
motifs
that
mediate
interactions
with
a
diverse
set
of
partner
proteins.
Through
its
tetraspanin-enriched
microdomains,
CD81
associates
with
other
tetraspanins
and
transmembrane
proteins
to
form
multi-protein
complexes
that
regulate
cell
signaling,
adhesion,
and
trafficking.
amplify
activation
and
antibody
responses.
It
also
influences
cell
adhesion
and
migration
by
interacting
with
integrins
and
with
other
tetraspanins,
thereby
shaping
how
cells
respond
to
their
environment
and
communicate
with
other
cells.
Hepatitis
C
virus
(HCV),
which
uses
CD81
in
combination
with
additional
entry
factors
to
infect
hepatocytes.
In
research
settings,
CD81
has
also
been
implicated
in
the
cellular
entry
or
trafficking
of
other
pathogens
and
in
the
handling
of
exosomes,
reflecting
its
broad
involvement
in
membrane
organization.
and
as
a
component
of
exosome
characterization,
and
it
remains
a
focus
of
studies
on
immune
signaling,
infectious
disease,
and
cancer
biology.