and Immunity (2003) 4, 168–169 & 2003 Nature Publishing Group All rights reserved 1466-4879/03 $25.00 www.nature.com/gene BRIEF COMMUNICATION Enhanced frequency of a PTPRC (CD45) exon A mutation (77C-G) in systemic sclerosis

R Schwinzer1, T Witte2, J Hundrieser1, S Ehlers1, T Momot2, N Hunzelmann3, T Krieg3, RE Schmidt2 and K Wonigeit1 1Transplantationslabor, Klinik fu¨r Viszeral- und Transplantationschirurgie, Zentrum Chirurgie; 2Abteilung Klinische Immunologie, Zentrum Innere Medizin, Medizinische Hochschule Hannover; 3Abteilung Dermatologie, Universita¨tKo¨ln, Germany

A point mutation in exon A (C to G transversion at position 77) of human PTPRC (CD45) has recently been associated with the development of multiple sclerosis (MS) for at least a subgroup of patients. In the present report, we studied the frequency of the 77C-G transversion in two other autoimmune diseases namely systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). The mutation was found with significantly enhanced frequency in patients suffering from SSc suggesting that PTPRC could play a role as susceptibility not only in MS but also in other autoimmune diseases. Further understanding of the mode of interaction of mutant PTPRC with other susceptibility genes may uncover mechanisms common in various autoimmune disorders. Genes and Immunity (2003) 4, 168–169. doi:10.1038/sj.gene.6363894

Keywords: human; CD45 polymorphism; -tyrosine phosphatase; systemic sclerosis; modifier gene

The transmembrane protein-tyrosine phosphatase CD45 to controls the difference was statistically not significant. plays a crucial role in the regulation of various immune All individuals carrying the mutation carried it in the responses.1 The CD45 protein is encoded by a single gene heterozygous state. Peripheral blood mononuclear cells (PTPRC; protein-tyrosine phosphatase, receptor-type C) (PBMC) from two SLE and one SSc patient with mutant and different isoforms can be generated by alternative could be analyzed by flow cytometry and showed splicing of three variable exons A, B, and C. In humans, a the typical variant CD45RA expression pattern on 77C-G mutation in exon A has been described which lymphocytes, monocytes, and granulocytes.8 This is in does not change the protein sequence but prevents line with previous findings suggesting that the point proper splicing of the exon thereby leading to a variant mutation is always associated with defective splicing expression pattern of CD45RA isoforms on leucocytes.2,3 generating a highly characteristic phenotype in affected Recent data studying three independent groups of individuals2,9 German patients suggest that the exon A mutation could The significantly enhanced frequencies of 77C-Gin be associated with an enhanced risk for the development SSc (7.5%; Table 1) as well as in MS patients (6–7%)4 as of multiple sclerosis (MS).4 Although subsequent studies compared to controls (1.5%) indicate a higher risk for failed to detect an association in other MS cohorts5,6 data heterozygous carriers to develop SSc or MS. We did not from CD45-manipulated animal models also point to a find a significant association of the mutation with SLE. role of CD45 in the control of autoimmune processes.7 However, the detection of the 77G allele in four out of 98 We therefore assumed that 77C-G in humans may not patients (4.1%; Table 1) warrants further studies and is in only be found in MS but also in other autoimmune line with the assumption that PTPRC could play a role as diseases. To test this hypothesis the frequency of the susceptibilty gene in several autoimmune diseases. mutation was determined in 67 patients with systemic Abnormal CD45 splicing may also be associated with a sclerosis (SSc) and 98 patients with systemic lupus higher risk of infection with some organisms since 5.6% erythematosus (SLE). Samples obtained from 205 healthy of HIV-1 patients have recently been reported to carry individuals were used as controls. the 77C-G mutation.10 Furthermore, two families with a The 77G allele was detected in five SSc patients and in similar splice defect associated with haemophagocytic three out of 205 control individuals (Table 1). Statistical lymphohistiocytosis and erythrocytic haemophagocyto- analysis revealed that the association of the point sis have been described.11,12 mutation with SSc is significant (P ¼ 0.029). The mutation Susceptibility to systemic lupus erythematosus, or was also found in four SLE patients. However, compared systemic sclerosis is regarded to be determined by multiple genetic factors.13,14 As in other complex diseases the number of susceptibility genes and their mode of Correspondence: Reinhard Schwinzer, Transplantationslabor, Klinik fu¨r Viszeral- und Transplantationschirurgie, Medizinische Hochschule Hann- inheritance are not known in detail yet. One approach to over, Carl-Neuberg-Str. 1, 30623 Hannover, Germany. address this question is genome-wide linkage studies E-mail: [email protected] to identify the chromosomal position of potential PTPRC (CD45) in autoimmune diseases R Schwinzer et al 169 Table 1 Frequency of the PTPRC exon A mutation (77C-G)in dimerization of CD45 molecules known to be required healthy controls and patientsa for proper regulation of their phosphatase activity, or (iii)

b d interfering with processes leading to the exclusion of Group Number of tested Number of P CD45 molecules from membrane rafts involved in the individuals individuals carrying 77C-Gc formation of the . Studying appropriate cell populations from carriers of the muta- Controls 205 3 — tion will allow to analyse whether such effects can be Patients demonstrated in vitro and in which way they might be Systemic sclerosis 67 5 0.029 Systemic 98 4 0.223 related to the development of autoimmune processes. lupus erythematosus aThe frequency of the point mutation was determined by analyzing genomic DNA isolated by commercially available kits (Qiagen, Acknowledgements Hilden, Germany) from peripheral blood samples. bHealthy blood donors recruited at the Department of Transfusion This work was supported by the Deutsche Forschungs- Medicine and the Transplant Immunology Laboratory, Medical gemeinschaft (Grant Schw437-2), Deutsche Stiftung School of Hannover, were used as control group. SSc patients were Sklerodermie, and Bundesministerium fu¨ r Bildung und recruited at the Department of Clinical Immunology, Hannover, and Forschung (Kompetenznetz ’’Rheuma’’; Grant C2.12). the Department of Dermatology, University of Koln.. All SLE patients were recruited at the Department of Clinical Immunology, Hannover. Only unrelated patients were studied. The study was approved by the local ethic committee, and all patients gave written References informed consent. cThe presence of 77C-G was demonstrated by RFLP analysis. The 1 Penninger JM, Irie-Sasaki J, Sasaki T, Oliveira-dos-Santos AJ. transversion changes the sequence of exon A from CCCG to CCGG CD45: new jobs for an old acquaintance. Nature Immunol 2001; which can be detected by restriction digestion with MspI. The 2: 389–396. cuts the mutant allele into two bands whereas the wild-type 2 Schwinzer R, Wonigeit K. Genetically determined lack of À allele remains undigested. Details of the methodology have been CD45R T cells in healthy individuals. Evidence for a described elsewhere.3 All individuals carrying the mutation were regulatory polymorphism of CD45R expression. heterozygous. J Exp Med 1990; 171: 1803–1808. d 3 Thude H, Hundrieser J, Wonigeit K, Schwinzer R. A point The exact test of Fisher was applied to test for association between mutation in the human CD45 gene associated with defective SSc patients and controls and SLE patients and controls for the exon splicing of exon A. Eur J Immunol 1995; 25: 2101–2106. A (C77G) mutation at the 5% test-level. The difference between 4 Jacobsen M, Schweer D, Ziegler A et al. A point mutation in controls and SSc patients was statistically significant. There was no PTPRC (CD45) is associated with the development of multiple significant association between the mutation and SLE (power, 16%). sclerosis. Nature Gen 2000; 26: 495–499. 5 Vorechovsky I, Kralovicova J, Tchilian E et al. Does 77C G in PTPRC modify autoimmune disorders linked to the major susceptibility loci with the aim to subsequently identify histocompatibility ? Nature Gen 2001; 29: 22–24. the relevant gene(s). An alternative approach taken in 6 Barcellos LF, Caillier S, Dragone L et al. PTPRC (CD45) is not associated with the development of multiple sclerosis in US this study is the analysis of associations with known patients. Nature Gen 2001; 29: 23–24. polymorphisms of genes potentially involved in the 7 Majeti R, Xu Z, Parslow TG et al. An inactivating point pathogenesis of a disease (candidate genes). Although mutation in the inhibitory wedge of CD45 causes lympho- the 77C-G mutation is present in the normal population proliferation and autoimmunity. Cell 2000; 103: 1059–1070. with a frequency of 1–2% it is obvious that the vast 8 Schwinzer R, Schraven B, Kyas U, Meuer SC, Wonigeit K. majority of carriers are healthy as the overall prevalence Phenotypical and biochemical characterization of a variant of SSc and SLE is about 10/100 000 and 50/100 000 CD45R expression pattern in human leukocytes. Eur J Immunol individuals, respectively, and only 4–8% of the diseased 1992; 22: 1095–1098. individuals carry the mutation. Thus, the 77C-G 9 Tchilian EZ, Wallace DL, Imami N et al. The exon A (C77G) polymorphism contributes to disease susceptibility only mutation is a common cause of abnormal CD45 splicing in humans. J Immunol 2001; 166: 6144–6148. in the context of additional genetic and possibly also 10 Tchilian EZ, Wallace DL, Dawes R et al. A point mutation in environmental factors. CD45 may be associated with an enhanced risk of HIV-1 In individuals carrying 77C-G, CD45RA molecules infection. AIDS 2001; 15: 1892–1894. are strongly expressed on cells which normally express 11 Wagner R, Morgan G, Strobel S. A prospective study of CD45 only the low molecular mass CD45R0 isoform (eg isoform expression in haemophagocytic lymphohistiocytosis; memory and activated T cells). Since CD45RA and an abnormal inherited immunophenotype in one family. Clin CD45R0 isoforms differentially influence T-cell receptor Exp Immunol 1995; 99: 216–219. as well as receptor-induced signal transduction1 12 Bujan W, Schandene L, Ferster A, De Valck C, Goldman M, it is conceivable that continuous overexpression of Sariban E. Abnormal phenotype in familial erythropha- gocytic lymphohistiocytosis. Lancet 1993; 342: 1296. CD45RA molecules could change the patterns of im- 13 Kotzin BL. Systemic lupus erythematosus. Cell 1996; 85: mune responsiveness in affected individuals. The aber- 303–306. rant expression pattern of CD45RA molecules might 14 Tan FK, Arnett FC. Genetic factors in the etiology of systemic affect signalling mechanisms by (i) altering the binding sclerosis and Raynaud phenomenon. Curr Opin Rheumatol pattern of CD45 ligands, (ii) disturbing ligand-induced 2000; 12: 509–511.

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