The CD45 antigen is a haemopoietic cell specific tyrosine phosphatase essential for antigen receptor mediated signalling in lymphocytes. Expression of different patterns of alternatively spliced CD45 isoforms is associated with distinct functions. We recently identified a polymorphism in exon 6 (A138G) of the gene encoding CD45 (PTPRC) that results in altered CD45 splicing. The 138G allele is present at a high frequency among Japanese (23.7%), with 5.1% individuals homozygous for the G allele. In this study we show that the A138G polymorphism is the cause of altered CD45 isoform expression, promoting splicing towards low molecular weight CD45 isoforms. We further report that the frequency of A138G heterozygotes is significantly reduced in number in cohorts of patients with autoimmune Graves' disease or hepatitis B infection, whereas G138G homozygotes are absent from a cohort of Hashimoto's thyroiditis patients. We also show that 138G individuals exhibit altered cytokine production in vitro and an increased proportion of memory T cells. These data suggest that the 138G variant allele strongly influences these diseases by modulation of immune mechanisms and may have achieved its high frequency as a result of a natural selection probably related to pathogen resistance.

Expression of the CD45 Ag in hemopoietic cells is essential for normal development and function of lymphocytes, and both mice and humans lacking expression exhibit SCID. Human genetic variants of CD45, the exon 4 C77G and exon 6 A138G alleles, which alter the pattern of CD45 isoform expression, are associated with autoimmune and infectious diseases. We constructed transgenic mice expressing either an altered level or combination of CD45 isoforms. We show that the total level of CD45 expressed is crucial for normal TCR signaling, lymphocyte proliferation, and cytokine production. Most importantly, transgenic lines with a normal level, but altered combinations of CD45 isoforms, CD45RABC/+ and CD45RO/+ mice, which mimic variant CD45 expression in C77G and A138G humans, show more rapid onset and increased severity of experimental autoimmune encephalomyelitis. CD45RO/+ cells produce more TNF-α and IFN-γ. Thus, for the first time, we have shown experimentally that it is the combination of CD45 isoforms that affects immune function and disease.

The CD45 antigen is essential for normal antigen receptor-mediated signalling in lymphocytes, and different patterns of splicing of CD45 are associated with distinct functions in lymphocytes. Here we show that abnormal CD45 splicing caused by a C77G transversion in exon A of the gene encoding CD45 (PTPRC) is associated with increased susceptibility to HIV-1 infection.

CD45 (leukocyte common)T he leukocyte common antigen CD45 is an abundant tyrosine phosphatase expressed on all leukocytes (1). The phosphatase activity of CD45 is essential for lymphocyte antigen receptor signal transduction. CD45 can also function as a Janus kinase phosphatase, negatively regulating cytokine receptor signaling (2). Both CD45 knockout mice (3, 4) and humans lacking CD45 expression (5, 6) are severely immunodeficient, with very few peripheral T lymphocytes and impaired T and B cell responses. These studies provide evidence for the crucial role of CD45 in the proper functioning of the immune system. Multiple CD45 isoforms can be generated by alternative splicing of exons 4 (A), 5 (B), and 6 (C) of the extracellular domain (7). CD45 alternative splicing is highly conserved between species and is tightly regulated. In humans, naive T cells express high-molecular-weight CD45 isoforms recognized by CD45RA mAbs. Activation of the cells results in a change of expression to low-molecular-weight isoforms detected by a CD45R0 mAb (8).These two major subsets of T lymphocytes expressing CD45RA and CD45R0 have been termed naive and memory cells. A polymorphism (C77G) in exon 4 of CD45 causing abnormal CD45 splicing has been described in humans (9). Activated or memory lymphocytes in these individuals continue to express both high-CD45RA and low-molecular-weight CD45R0 isoforms, in contrast to the normal pattern of lowmolecular-weight CD45R0 isoform expression. Recently, another point mutation in exon 4 of CD45 (C59A) causing aberrant splicing has been identified, but it appears to be relatively rare (10).The C77G polymorphism and abnormal CD45 splicing have been further linked to the development of multiple sclerosis in German (11) and Italian (12) patient cohorts, although other studies do not support such an association (13,14). We have shown an increased frequency of the C77G variant allele in HIV-1-infected individuals in the United Kingdom (15). All of these observations suggest that abnormal CD45 splicing is associated with altered immunological function, autoimmunity, and viral infections.Here we report a polymorphism in exon 6 A138G in the gene encoding CD45 with a very high prevalence in Japanese and Korean populations. We analyzed the expression of CD45 isoforms in peripheral blood mononuclear cells (PBMC) of individuals homozygous and heterozygous for the A138G variant. Our results show that T cells in individuals carrying the A138G allele display altered cell-surface CD45 isoform expression because of changes in alternative splicing. Analysis of exon 6 A138G and exon 4 C77G variants in different populations showed striking differences in the frequency and distribution of these mutations, suggesting effects of natural selection. Materials and MethodsMaterials. One hundred seventy-five Japanese genomic DNAs were collected from Osaka City University Medical School (Osaka), of which 49 were from patients with malignant gynecological cancer. PBMC were isolated by centrifugation on a Ficoll-Paque (Amers...

Transgenic mice have been constructed expressing high (CD45RABC) and low (CD45R0) molecular weight CD45 isoforms on a CD45-/- background. Phenotypic analysis and in vivo challenge of these mice with influenza and lymphocytic choriomeningitis viruses shows that T cell differentiation and peripheral T cell function are related to the level of CD45 expression but not to which CD45 isoform is expressed. In contrast, B cell differentiation is not restored, irrespective of the level of expression of a single isoform. All CD45 trangenic mice have T cells with an activated phenotype and increased T cell turnover. These effects are more prominent in CD8 than CD4 cells. The transgenic mice share several properties with humans expressing variant CD45 alleles and provide a model to understand immune function in variant individuals.

Background: A polymorphism in exon 4 (C77G) of CD45 that alters CD45 splicing has been associated with autoimmune and infectious diseases in humans. Objective: To investigate the effect of C77G in hepatitis C virus (HCV) infected individuals and study the phenotype and function of peripheral blood mononuclear cells (PBMC) from healthy and hepatitis C infected C77G carriers. Results: C77G individuals showed an increased proportion of primed CD45RA and effector memory CD8 T cells and more rapid activation of the lymphocyte specific protein tyrosine kinase (Lck) following CD3 stimulation. Transgenic mice with CD45 expression mimicking that in human C77G variants had more activated/memory T cells, more rapid proliferative responses, and activation of Lck. Conclusions: Changes in CD45 isoform expression can alter immune function in human C77G variants and CD45 transgenic mice. The C77G allele may influence the outcome of HCV infection.

CD45 is a leukocyte tyrosine phosphatase, essential for normal immune responses. We have studied the function of splenic dendritic cells of CD45 +/+ , CD45 -/-, CD45RABC and CD45RO transgenic mice. We show that there are increased numbers of plasmacytoid dendritic cells in CD45 -/-mice. DC of all mice are capable of responding to lymphocytic choriomeningitis virus (LCMV) infection by up-regulation of MHC and costimulatory molecules. DC of CD45 -/-mice have an impaired capacity to produce type I interferons in response to LCMV infection in vivo. These data indicate that lack of CD45 expression in DC has a profound effect on their function. This is largely restored by CD45RABC or CD45RO transgenes.

Hemophagocytic lymphohistiocytosis (HLH) and Langerhans cell histiocytosis (LCH) are members of a group of rare heterogenous disorders, the histiocytoses, characterized by uncontrolled accumulation of pleomorphic infiltrates of leukocytes. The etiology of these diseases is mainly unknown. CD45 is a hemopoietic cell specific tyrosine phosphatase essential for antigen receptor mediated signaling in lymphocytes and different patterns of CD45 splicing are associated with distinct functions. Recently a polymorphism (C77G) in exon 4 of CD45 causing abnormal CD45 splicing and a point mutation affecting CD45 dimerization were implicated in multiple sclerosis in humans and lymphoproliferation and autoimmunity in mice respectively. Here we show that two patients with HLH exhibited abnormal CD45 splicing caused by the C77G variant allele, while a further 21 HLH patients have normal CD45. We have also examined 62 LCH patients and found three to have the C77G mutation. Peripheral blood thymus-derived (T) CD8ϩ cells from normal individuals carrying the C77G mutation show a significant decrease in the proportion of cells expressing L-selectin and increased frequency of cells with LFA-1 hi expression. It remains to be established whether C77G is a contributing factor in these histiocytic disorders. The leukocyte common antigen CD45 is an abundant tyrosine phosphatase, essential for lymphocyte antigen receptor signal transduction (1). Both CD45 knockout mice (2, 3) and humans lacking CD45 expression (4, 5) are severely immunodeficient with very few peripheral T lymphocytes and impaired T and B cell responses.Multiple CD45 isoforms can be generated by alternative splicing of exons A, B, and C of the extracellular domain (6, 7). In humans naïve T cells express high molecular weight CD45 isoforms, recognized by CD45RA MAb ("CD45RA" cells), but activation of the cells results in a change to expression of low molecular weight isoforms, detected by a CD45R0 MAb ("CD45R0" or memory cells) (8). Paragraph deleted. Several polymorphisms of the gene encoding CD45 (PTPRC at 1q31-32) have been described and several of these cause altered splicing (9 -14).The C77G polymorphism (9 -12) has been linked to the development of multiple sclerosis in German (15)