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Immunopathology
Published in Constantin A. Bona, Francisco A. Bonilla, Textbook of Immunology, 2019
Constantin A. Bona, Francisco A. Bonilla
Some hemagglutinins react poorly with red cells at 37°C, but well at temperatures below 32°C. These are called cold-reactive antibodies or cold agglutinins. AHD caused by these antibodies is called paroxysmal cold hemoglobinuria or cold agglutinin disease. In both of these conditions, hemolysis only occurs when either the body or a part of it is exposed to cold. Cold agglutinins use a restricted set of V genes derived from the VH4 and VXIII families.
Hemolytic Anemias: General Considerations
Published in Harold R. Schumacher, William A. Rock, Sanford A. Stass, Handbook of Hematologic Pathology, 2019
The differential diagnosis is that of intravascular hemolysis (Table 2). Thrombotic thrombocytopenic purpura is the first item on the differential diagnosis of patients with intravascular hemolysis, fever, and altered mental status, but is largely ruled out by the absence of schistocytes on peripheral smear. Other mechanical etiologies of hemolysis are also ruled out by the blood smear and by history and physical examination. Disseminated intravascular coagulation rarely produces significant hemolysis, and is ruled out by normal coagulation studies. The catastrophic presentation of this hemolysis would be uncommon for paroxysmal nocturnal hemoglobinuria or for paroxysmal cold hemoglobinuria; the latter is largely ruled out by the absence of serologic evidence of syphilis. It would be unusual for a hereditary enzyme deficiency, such as G6PD deficiency, to present so late in life, but this does happen occasionally. The differential diagnosis after the initial laboratory evaluation is delayed hemolytic transfusion reaction versus a direct toxic effect; paroxysmal nocturnal hemoglobinuria or G6PD deficiency remain in the differential but are much less likely.
Haematology and oncology
Published in Ashley Bond, MRCP Part 2 Examination, 2017
2 Cold (paroxysmal cold haemoglobinuria): IgM mediatedintravascular haemolysis.
Current and emerging treatment options for autoimmune hemolytic anemia
Published in Expert Review of Clinical Immunology, 2018
Wilma Barcellini, Bruno Fattizzo, Anna Zaninoni
Autoimmune hemolytic anemia (AIHA) is a highly heterogeneous disease, caused by the increased destruction of red blood cells (RBCs) by anti-RBC autoantibodies with or without complement activation. AIHA has an incidence of 0.8–3 per 105/year in adults, a prevalence of 17:100,000, and middle-age and female predominance. It is diagnosed by anti-erythrocyte antibody demonstration through direct antiglobulin test (DAT) and classified according to the thermal range of the autoantibody in warm AIHA (wAIHA, typically DAT+ for anti-IgG, or IgG plus C), cold (cold agglutinin disease [CAD] due to IgM with DAT+ for C3d), mixed (DAT+ for both IgG and high-titer cold agglutinins), or atypical forms (DAT negative, IgA driven, and warm IgM AIHA) [1]. Among cold forms, it is worth mentioning paroxysmal cold hemoglobinuria (PCH), which is more common in children (30% of cases) and is caused by the Donath–Landsteiner autoantibody, a bithermic hemolysin able to fix complement at cold temperatures and to determine RBCs lysis at 37°C (Figure 1). The clinical spectrum ranges from fully compensated to life-threatening, due to the several pathogenic mechanisms involved that may differently act in the same patient at different time points [1–4]. Regardless the breakdown of immunologic tolerance, it is worth considering the functional abnormalities of B lymphocytes, the alteration of cytokine production and of immunoregulatory T cells, the pivotal role of the complement system, and the possible abnormal presentation of autoantigens. The main players involved in RBC destruction are autoantibodies, whose pathogenicity depends on their class, thermal amplitude, and affinity/efficiency in activating complement. Other important mechanisms are antibody-dependent cellular cytotoxicity (ADCC) and cytotoxic effectors (CD8+ T and natural killer cells). Activated macrophages carrying Fc receptors may recognize and phagocyte erythrocytes opsonized by autoantibodies and complement. While direct complement-mediated lysis takes place mainly in the circulations and liver, ADCC and phagocytosis occur preferentially in the spleen and lymphoid organs. Finally, the efficacy of the erythroblastic compensatory response can greatly influence the clinical picture of AIHA [1,5].