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Blood, Vol. 95 No. 3 (February 1), 2000:
pp. 1069-1077
Cell-specific, activation-dependent regulation of neutrophil
CD32A ligand-binding function
Shanmugam Nagarajan,
Kala Venkiteswaran,
Michael Anderson,
Umar Sayed,
Cheng Zhu, and
Periasamy Selvaraj
From the Department of Pathology and Laboratory Medicine, Emory
University School of Medicine, and the School of Mechanical
Engineering, Georgia Institute of Technology, Atlanta, GA.
Neutrophils express 2 low-affinity Fc R, FcRIIIB (CD16B), and
FcRIIA (CD32A). CD16B is a glycosyl-phosphatidyl inositol-anchored molecule, whereas CD32A is a polypeptide-anchored molecule. These 2 receptors also differ in their signaling. The biological significance of coexpression of 2 FcRs with distinct membrane anchors and signaling capacities is not clearly understood. Using neutrophils from
a CD16B-deficient donor and normal neutrophils treated with anti-CD16
monoclonal antibodies, the authors demonstrated that affinity
modulation of CD32A is one of the mechanisms by which neutrophils
regulate their FcR-dependent functions. Neutrophils isolated from a CD16B donor rosetted poorly with sheep
erythrocytes opsonized with rabbit IgG (EA) (12% ± 2% versus
80% ± 6% for control) and were unable to mediate
immunophagocytosis. However, activation of CD16B
neutrophils with fMLP, a bacterial chemotactic peptide, increased the
CD32A-dependent EA rosetting to 58%. The CD32A-dependent rosetting of
fMLP-activated normal neutrophils also increased nearly 5-fold, but
there was no increase in CD32A expression. The CD32A-dependent immune
complex (IC) binding was also increased in activated neutrophils. This
affinity regulation was not observed with CD32A expressed on Chinese
hamster ovary cells. These results suggest that in resting neutrophils
CD32A is in a low-affinity state and that these cells primarily engage
CD16B for IC binding. However, once the neutrophils are activated, the
CD32A is converted to a high-affinity state that leads to
CD32A-dependent ligand binding and signaling. These results suggest
that neutrophils adopt a novel strategy to engage the 2 different
FcR selectively during physiologic and pathologic conditions to
carry out their functions efficiently.
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