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Molecular and Cellular Biology, September 2005, p. 8052-8063, Vol. 25, No. 18
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.18.8052-8063.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Regulation of In Vitro and In Vivo Immune Functions by the Cytosolic Adaptor Protein SKAP-HOM

M. Togni,^1, K. D. Swanson,^2, S. Reimann,¹ S. Kliche,¹ A. C. Pearce,³ L. Simeoni,¹ D. Reinhold,¹ J. Wienands,⁴ B. G. Neel,² B. Schraven,^1* and A. Gerber¹

Institute of Immunology, Otto von Guericke University, Magdeburg,¹ Cellular and Molecular Immunology, Georg August University, Göttingen, Germany,⁴ Cancer Biology Program, Division of Hematology-Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts,² Centre for Cardiovascular Sciences, Division of Medical Sciences, Institute of Biomedical Research, Wolfson Drive, The Medical School, University of Birmingham, Edgbaston, Birmingham, United Kingdom³

Received 24 March 2005/ Returned for modification 6 May 2005/ Accepted 17 June 2005

SKAP-HOM is a cytosolic adaptor protein representing a specific substrate for the Src family protein tyrosine kinase Fyn. Previously, several groups have provided experimental evidence that SKAP-HOM (most likely in cooperation with the cytosolic adaptor protein ADAP) is involved in regulating leukocyte adhesion. To further assess the physiological role of SKAP-HOM, we investigated the immune system of SKAP-HOM-deficient mice. Our data show that T-cell responses towards a variety of stimuli are unaffected in the absence of SKAP-HOM. Similarly, B-cell receptor (BCR)-mediated total tyrosine phosphorylation and phosphorylation of Erk, p38, and JNK, as well as immunoreceptor-mediated Ca²⁺ responses, are normal in SKAP-HOM^–/– animals. However, despite apparently normal membrane-proximal signaling events, BCR-mediated proliferation is strongly attenuated in the absence of SKAP-HOM^–/–. In addition, adhesion of activated B cells to fibronectin (a ligand for ß1 integrins) as well as to ICAM-1 (a ligand for ß2 integrins) is strongly reduced. In vivo, the loss of SKAP-HOM results in a less severe clinical course of experimental autoimmune encephalomyelitis following immunization of mice with the encephalitogenic peptide of MOG (myelin oligodendrocyte glycoprotein). This is accompanied by strongly reduced serum levels of MOG-specific antibodies and lower MOG-specific T-cell responses. In summary, our data suggest that SKAP-HOM is required for proper activation of the immune system, likely by regulating the cross-talk between immunoreceptors and integrins.

M. Togni and K. D. Swanson contributed equally to this work.

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