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CD33 146 CD42b
aggregated immunoglobulin/immune complexes. Several
different isoforms that are coded for by closely related genes
exist. D32 is found on granulocytes, B cells, monocytes,
platelets, and endothelial cells. FcγRII functions as the receptor
for aggregated IgG and is involved in cell activation.
CD33
An antigen (molecular weight of 67 kDa) that is a single
chain transmembrane glycoprotein. It is restricted to myeloid
cells and is found on early progenitor cells, monocytes,
myeloid leukemias, and weakly on some granulocytes.
CD34
A single chain transmembrane glycoprotein (molecular
weight of 105 to 120 kDa) present on immature haematopoietic
cells and endothelial cells as well as bone
marrow stromal cells. Three classes of CD34 epitopes
have been defined by differential sensitivity to enzymatic
cleavage with neuraminidase and with glycoprotease from
Pasteurella haemolytica. Its gene is on chromosome 1. It is
the ligand for L-selectin (CD62L).
CD35
An antigen that is known as CR1 that binds C3b and C4b.
The CD35 antigen includes four different allotypes, C, A,
B, and D, with molecular weights of 160, 190, 220, and 250
kDa, respectively. The antigen is widely distributed on various
cell types, including erythrocytes, B cells, monocytes,
granulocytes (negative on basophils), some natural killer
(NK) cells, and follicular dendritic cells. The functions of
CR1 are the processing of immune complexes and promotion
of binding and phagocytosis of C3b-coated particles/cells.
CD36
An antigen (molecular weight of 88 kDa) that is a single
chain membrane glycoprotein found on monocytes, macrophages,
platelets, some endothelial cells, and weakly on
B cells. The CD36 antigen is also referred to as gpIV or
gpIIIb. The antigen acts as a receptor for thrombospondin
and collagen. Furthermore, it is the endothelial cell receptor
for erythrocytes infected with Plasmodium falciparum.
CD37
A B cell antigen (molecular weight of 40 to 52 kDa) that is
an integral glycoprotein that appears at the late pre-B cell
stage and then persists throughout B cell maturation until
shortly before the terminal plasma cell stage. The antigen is
also weakly expressed on macrophages, on neutrophils and
monocytes, and on resting and activated T cells. The function
of CD37 antigen is unknown.
CD38
A molecule that is an integral glycoprotein and is also
referred to as the T10 antigen. It has a molecular weight of
45 kDa and is found on plasma cells, pre-B cells, immature
T cells, and activated T cells.
CD39
An antigen (molecular weight of 100 to 70 kDa) that is
present on a number of cell types, including B cells (mantle
zone), most mature B cells with surface-bound immunoglobulin
G (IgG), monocytes, some macrophages, and vascular
endothelial cells. Its function is yet to be determined,
but it may mediate B cell adhesion. Also called gp80.
CD40
An integral membrane glycoprotein (molecular weight of
48/44 kDa) that is also referred to as gp50. The antigen
shares similarities with many nerve growth factor receptors.
The CD40 antigen is expressed on peripheral blood and
tonsillar B cells from the pre-B cell stage until the plasma
cell stage, where it is lost. It is also expressed on B cell
leukemias and lymphomas, on some carcinomas, weakly on
monocytes, and on interdigitating cells. The CD40 antigen
is active in B cell proliferation. The CD40 ligand is gp39.
CD40 binds CD40-L, the CD40 ligand. It is the receptor
for the costimulatory signal for B cells. Its interaction with
CD40 ligand on T cells induces B cell proliferation. CD40
belongs to the TNF receptor family of molecules.
CD40-L
A 39-kDa antigen present on activated CD4 + T cells. It is
the ligand for CD40. It is also called T-BAM or gp39.
CD40 ligand
A molecule on T cells that interacts with CD40 on B cell
proliferation.
CD41
An antigen, equivalent to glycoprotein IIb/IIIa, that is found
on platelets and megakaryocytes. This structure is a Ca 2+ -
dependent complex between the 110-kDa gpIIIa (CD61) and
the 135-kDa gpIIb molecules. The gpIIb molecule consists
of two chains: an α chain of 120 kDa and a β chain of 23
kDa. The gpIIIa (CD61) is a single chain protein, but both
gpIIIa (CD61) and gpIIb contain transmembrane domains.
The molecule is a receptor for fibrinogen, but it also binds
von Willebrand factor, thrombospondin, and fibronectin.
It is absent or reduced in Glanzmann’s thrombasthenia
(hereditary gpIIb/IIIa deficiency). It has a role in platelet
aggregation and activation.
CD42a
An antigen, equivalent to glycoprotein IX, that is a single
chain membrane glycoprotein with a molecular weight of
23 kD. It is found on megakaryocytes and platelets. CD42a
forms a noncovalent complex with CD4b (gpIb) which
acts as a receptor for von Willebrand factor. It is absent or
reduced in the Bernard–Soulier syndrome.
CD42bα
CD42a
COOH
COOH
CD42bβ
CD42b
An antigen, equivalent to glycoprotein Ib, that is a twochain
membrane glycoprotein with a molecular weight of
s s
COOH
Lau-rich repeats
Structure of CD42.