Volume 54, Issue 5 pp. 1543-1556
Research Article

Impaired recognition of apoptotic neutrophils by the C1q/calreticulin and CD91 pathway in systemic lupus erythematosus

Suzanne Donnelly

Suzanne Donnelly

John Radcliffe Hospital and University of Oxford, Oxford, UK

Search for more papers by this author
Wendy Roake

Wendy Roake

University of Oxford, Oxford, UK

Search for more papers by this author
Simon Brown

Simon Brown

University of Edinburgh Medical School, Edinburgh, UK

Search for more papers by this author
Philip Young

Philip Young

Peninsula Medical School, Exeter, UK

Search for more papers by this author
Haley Naik

Haley Naik

University of Oxford, Oxford, UK

Search for more papers by this author
Paul Wordsworth

Paul Wordsworth

John Radcliffe Hospital, Oxford, UK

Search for more papers by this author
David A. Isenberg

David A. Isenberg

University College, London, UK

Search for more papers by this author
Kenneth B. M. Reid

Kenneth B. M. Reid

University of Oxford, Oxford, UK

Search for more papers by this author
Paul Eggleton

Corresponding Author

Paul Eggleton

University of Oxford, Oxford, and Peninsula Medical School, Exeter, UK

Institute of Biomedical and Clinical Sciences, Peninsula Medical School, Heavitree Road, Exeter, Devon EX1 2LU, UKSearch for more papers by this author
First published: 27 April 2006
Citations: 116

Abstract

Objective

A deficiency in a subcomponent of C1q can result in increased susceptibility to autoimmune diseases such as systemic lupus erythematosus (SLE). The monocyte endocytic receptor CD91 is implicated in the endocytosis of apoptotic neutrophils via interactions with C1q and calreticulin. In this clinical study, we studied the binding of C1q to leukocytes and determined whether C1q bound specifically to calreticulin and CD91 on cells undergoing apoptosis in SLE.

Methods

Proximal antibody phage display, calreticulin-transfected cells, and immunocytochemical and confocal techniques were used in a comprehensive analysis of direct binding of C1q to apoptotic neutrophils that were obtained from healthy individuals and from patients with SLE. In addition, apoptotic cellular systems were assessed in vitro.

Results

C1q appeared to colocalize to apoptotic blebs on the surface of leukocytes in association with both calreticulin and CD91, as determined by phage display and transfected cell studies. However, C1q did not bind to apoptotic cells isolated from SLE patients, despite the positivity of the cells for both calreticulin and CD91. Surface expression of calreticulin decreased on neutrophils as they aged, but increased on monocytes. In an apoptotic phagocytic assay, the addition of C1q and calreticulin significantly enhanced the phagocytosis of apoptotic cell debris by monocyte-derived cells.

Conclusion

These observations indicate that neutrophils from SLE patients have a reduced ability to be recognized and removed by the C1q/calreticulin/CD91-mediated apoptotic pathway, despite the presence of main apoptotic recognition partners. This suggests that an additional component, as yet unidentified, acts as a C1q binding partner on apoptotic cells, and this component may be lacking in cells isolated from SLE patients.

The full text of this article hosted at iucr.org is unavailable due to technical difficulties.

click me