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CD42c 147 CD45RO
170 kDa. CD42b has an α chain of 135 kDa and a β chain
of 23 kDa. It is found on platelets and megakaryocytes. It
forms a noncovalent complex with CD42a (gpIX) which
acts as a receptor for von Willebrand factor. The antigen is
absent or reduced in the Bernard–Soulier syndrome.
CD42c
A 22-kDa antigen found on platelets and megakaryocytes. It
is also referred to as GPIB-β.
CD42d
An 85-kDa antigen present mainly on platelets and megakaryocytes.
It is also referred to as GPV.
CD43
A 90- to 100-kDa sialylated glycoprotein found on leukocytes,
including T cells, granulocytes, erythrocytes,
epithelial cell lines, and brain cells. The CD43 antigen is
not present on peripheral B cells. The molecule is involved
in activation of T cells, B cells, natural killer (NK) cells,
and monocytes. It binds CD54 (ICAM-1).
CD44
A ubiquitous multistructural and multifunctional cell surface
glycoprotein that participates in adhesive cell-to-cell
and cell-to-matrix interactions. It also plays a role in cell
migration and cell homing. Its main ligand is hyaluronic
acid (HA), hyaluronate, and hyaluronan. It is expressed
by numerous cell types of lymphohematopoietic origin,
including erythrocytes, T and B lymphocytes, natural killer
(NK) cells, macrophages, Kupffer cells, dendritic cells,
and granulocytes. It is also expressed in other types of cells
such as fibroblasts and central nervous system cells. In
addition to hyaluronic acid, CD44 also interacts with other
ECM ligands such as collagen, fibronectin, and laminin. In
addition to these functions, CD44 facilitates lymph node
homing via binding to high endothelial venules, presentation
of chemokines or growth factors to migrating cells, and
growth signal transmission. CD44 concentration may be
observed in areas of intensive cell migration and proliferation,
as in wound healing, inflammation, and carcinogenesis.
Many cancer cells and their metastases express high
levels of CD44. It may be used as a diagnostic or prognostic
marker for selected human malignant diseases.
CD45
An antigen that is a single chain glycoprotein referred to as
the leukocyte common antigen (or T200). It consists of at
least five high molecular weight glycoproteins present on
the surfaces of the majority of human leukocytes (molecular
weights of 180, 190, 205, and 220 kDa). The different
isoforms arise from a single gene via alternative mRNA
splicing. The variation among the isoforms is all in the
extracellular region. The larger (700-amino acid) intracellular
portion is identical in all isoforms and has protein
tyrosine phosphatase activity. It can potentially interact
with intracellular protein kinases such as p56 lck , which may
be involved in triggering cell activation. By dephosphorylating
proteins, CD45 would act in a fashion opposite that
of a protein kinase. It facilitates signaling through B and
T cell antigen receptors. Leukocyte common antigen (LCA)
is present on all leukocyte surfaces. It is a transmembrane
tyrosine phosphatase that is expressed in various isoforms
on different types of cells, including the different subtypes
of T cells. The isoforms are designated by CD45R followed
by the exon whose presence gives rise to distinctive
antibody-binding patterns.
P
COOH
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F3
F3
F3
CD45⎯tonsil.
CD45R
A subfamily that is now divided into three isoforms:
CD45RO, CD45RA, and CD45RB. The designation CD45R
has been maintained for those antibodies that have not been
tested on appropriate transfectants.
CD45RA
A 220/205-kDa isoform of CD45 (sequence encoded by
exon A) that is found on B cells, monocytes, and a subtype
of T cells. T cells expressing this isotype are naïve or virgin
T cells and nonprimed CD4 and CD8 cells.
CD45RB
A molecule consisting of four isoforms of CD45 (sequence
encoded by exon B), with molecular weights of 220, 205,
and 190 kDa, that is found on B cells, subset of T cells,
monocytes, macrophages, and granulocytes.
CD45RO
A 180-kDa isoform of CD45 (sequence not encoded by
exons A, B, or C) found on T cells, a subset of B cells,
monocytes, and macrophages. T cells expressing this antigen
are T memory cells or primed T cells.
P
Structure of CD45, also known as leukocyte common antigen.
C