Platelet and red blood cell phagocytosis kinetics are differentially controlled by phosphatase activity within mononuclear cells.

Abstract

BACKGROUND:

Anti-D treatment is effective in increasing platelet (PLT) counts in patients with autoimmune thrombocytopenic purpura (AITP); however, the exact mechanism of action is unknown. Previous results have suggested that anti-D-coated red blood cells (RBCs) affect reticuloendothelial system phagocytosis by stimulating agents (e.g., reactive oxygen species) that alter signaling pathways within the phagocyte. To address this, a flow cytometric assay was used to compare the kinetics and signaling pathways responsible for opsonized PLT and RBC phagocytosis.

STUDY DESIGN AND METHODS:

Human RBCs or PLTs were labeled with the fluorescent dye CM-Green, opsonized with Rh immune globulin or anti-MHC, respectively, and incubated with THP-1 monocytes with or without signal transduction inhibitors and intracellular fluorescence was analyzed.

RESULTS:

Compared with opsonized PLTs, phagocytosis of opsonized RBCs was significantly slower (p<0.0001) and, within 2 hours, induced a state of phagocytic refractoriness; resting the mononuclear cells (MNCs) for up to 24 hours did not rescue their ability to further mediate PLT phagocytosis. Inhibitors of phosphatidylinositol 3-kinase (wortmannin, LY294002, myricetin, and quercetin), protein kinase C (staurosporine), and Syk kinase (piceatannol) inhibited both opsonized RBC and opsonized PLT phagocytosis. In contrast, opsonized RBC phagocytosis was significantly (p<0.0001) enhanced by the tyrosine phosphatase inhibitor phenyl arsine oxide, whereas PLT phagocytosis was significantly reduced (p<0.0001). Of interest, phosphatase inhibition during opsonized RBC phagocytosis induced a longer (48 hr) phagocytic refractoriness period in the MNCs.

CONCLUSION:

These results suggest that the early kinetics and signaling events related to phosphatase activity regulate how mononuclear phagocytes engulf opsonized RBCs and induce phagocytic refractoriness for further PLT phagocytosis.

• Authors: Rukhsana Aslam, Michael Kim, Edwin R Speck, Arjuna Contram Seetanah, Steven Molinski, John Freedman, John W Semple
• Journal: Transfusion (Transfusion) Vol. 47 Issue 11 Pg. 2161-8 (Nov 2007) ISSN: 0041-1132 [Print] United States
• PMID: 17958546 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Opsonin Proteins
• Phosphoric Monoester Hydrolases

Topics

• Blood Platelets (immunology)
• Erythrocytes (immunology)
• Flow Cytometry
• Humans
• Kinetics
• Leukocytes, Mononuclear (enzymology, immunology)
• Opsonin Proteins (metabolism)
• Phagocytosis
• Phosphoric Monoester Hydrolases (immunology, metabolism)
• Signal Transduction