Increased red cell turnover in a line of CD22‐deficient mice is caused by Gpi1^c: A model for hereditary haemolytic anaemia

Abstract

CD22, an inhibitory co-receptor of the BCR, has been identified as a potential candidate gene for the development of autoimmune haemolytic anaemia in mice. In this study, we have examined Cd22 tm1Msn CD22-deficient mice and identified an increase in RBC turnover and stress erythropoiesis, which might be consistent with haemolysis. We then, however, eliminated CD22 deficiency as the cause of accelerated RBC turnover and established that enhanced RBC turnover occurs independently of B cells and anti-RBC autoantibodies. Accelerated RBC turnover in this particular strain of CD22-deficient mice is red cell intrinsic and appears to be the consequence of a defective allele of glucose phosphate isomerase, Gpi1 c . This form of Gpi1 was originally derived from wild mice and results in a substantial reduction in enzyme activity. We have identified the polymorphism that causes impaired catalytic activity in the Gpi1 c allele, and biochemically confirmed an approximate 75% reduction of GPI1 activity in Cd22 −/− RBCs. The Cd22 −/− .Gpi1 c congenic mouse provides a novel animal model of GPI1-deficiency, which is one of the most common causes of chronic non-spherocytic haemolytic anaemia in humans.Keywords: Anaemia r CD22 r Erythrocytes r Glucose-6-phosphate isomerase r Polymorphism Supporting Information available online IntroductionClearance of RBCs by anti-RBC auto-Ab gives rise to the condition known as autoimmune haemolytic anaemia (AIHA). The pathoCorrespondence: Dr. Kenneth G.C. Smith e-mail: kgcs2@cam.ac.uk logical mechanisms underlying the generation of anti-RBC autoantibodies are incompletely understood, but are likely to involve defects in both T-and B-cell tolerance [1,2]. New Zealand Black (NZB) mice spontaneously develop AIHA at around 6 months of age [3], which is characterised by a progressive anaemia of varying severity, accompanied by reticulocytosis and splenomegaly, the results of on-going stress erythropoiesis. There is a clear genetic contribution to AIHA in NZB mice, and a number of quantitative C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 3212-3222 Cellular immune response 3213 trait loci (QTLs) that either promote or protect from disease have been identified [4][5][6][7]. One such anaemia-promoting QTL, designated Aia3 (autoimmune anemia 3), is present on NZB proximal chromosome 7 and peaks in the vicinity of the Cd22 gene, around 9 cM from the centromere [7]. Of the many genes present within this interval, Cd22 is an attractive candidate for promoting Coombs auto-Ab production and AIHA [7]. As discussed below, NZB mice express a defective form of this receptor, and loss of CD22 function is associated with auto-Ab generation in some mouse models [8][9][10]. Other potential candidates include Cd79a, which encodes a component of the BCR signalling complex, and Fcgbp, which encodes an IgG-binding protein.CD22 is an inhibitory co-receptor of the BCR and, like other co-receptors, modulates the Ag receptor signal in response to cues from the local microen...

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

“…Increased hemolysis may be caused by dysfunction of RBCs correlated with (I) defects of Hb (hemoglobinopathies) (18, 94, 161, 199), including alterations in structure and function of Hb chains; (II) defects of cytoskeletal proteins such as spectrin and ankyrin, which are essential for maintaining cell shape and integrity (19, 134, 149, 169); (III) defects in metabolic enzymes catalyzing the pentose phosphate cycle (126, 147) such as deficiency of G6PDH; (IV) redox dysregulation and defects of antioxidant enzymes (63, 84); (V) presence of antibodies directed against surface antigens on RBCs, such as antibodies anti-A, or anti-B blood group antigens (formed as a consequence of transfusion of allogenic blood from the wrong blood group), or autoimmune antibodies resulting in enhanced damage of RBC membranes (14, 92, 124, 160, 164, 178); (VI) chronic inflammation, disorders of cytokine production, and chronic diseases (97, 105, 154); (VII) side effects of drug/poisoning (32); (VIII) other genetic defects (155, 187); or (IX) RBC extrinsic factors (102, 108, 113, 142, 180). Another important cause of anemia is the loss of RBCs due to acute or chronic bleeding (59).…”

The red blood cell as a novel regulator of human B‐cell activation

“…CD22 −/− gene‐deleted mice have been widely used to determine the role of CD22 as an inhibitory co‐receptor on B cells [ 32 ]. Further comparison of the detailed phenotype of such mice with our work is problematic because they can also carry other unintended genetic changes that result in, for example, an intrinsic RBC defect [ 33 ].…”