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INTRODUCTION

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  • Caused by autoantibodies that bind red cells best at temperatures below 37°C, usually below 31°C.

  • Mediated through two major types of "cold antibody": cold agglutinins and Donath-Landsteiner antibodies.

  • Clinical features vary considerably, but in both types, the complement system plays a major role in red cell destruction.

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COLD AGGLUTININ-MEDIATED AUTOIMMUNE HEMOLYTIC ANEMIA

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  • Cold agglutinins are IgM autoantibodies that agglutinate red cells optimally between 0°C and 5°C. Complement fixation occurs at higher temperatures.

  • Classified as either primary (chronic cold agglutinin disease) or secondary (generally as a result of Mycoplasma pneumoniae infection or Epstein-Barr virus (EBV)–related infectious mononucleosis) (see Table 25–1).

  • Peak incidence for the primary (chronic) syndrome is in persons older than 50 years.

  • This disorder characteristically has monoclonal IgM cold agglutinins and may be considered a symptomatic monoclonal gammopathy.

  • Some patients develop a B-cell lymphoproliferative disorder (e.g. Waldenström macroglobulinemia).

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Table Graphic Jump Location
TABLE 25–1AUTOIMMUNE HEMOLYTIC ANEMIA: COLD ANTIBODY TYPE*
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Pathogenesis

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  • The specificity of cold agglutinins is usually against I/i antigens. I is expressed heavily in adult red cells, weakly on neonatal red cells. The reverse is true of the i antigen, which also may still be expressed on reticulocytes.

  • High proportions of IgM cold agglutinins with either anti-I or anti-i specificity have heavy-chain variable regions encoded by VH4–34, a conserved immunoglobulin variable region gene.

  • Naturally occurring cold agglutinins are present in low titer (less than 1:32) in normal persons. Transient hyperproduction of less clonally restricted antibodies occurs in the recovery phase of infections, such as EBV, mycoplasma, or cytomegalovirus.

  • I/i antigens serve as mycoplasma receptors, which may lead to altered antigen presentation and to subsequent autoantibody production.

  • In B-cell lymphomas, cold agglutinins may be produced by the malignant cells.

  • The highest temperature at which antibodies can cause red cell agglutination is termed the thermal amplitude. The higher the thermal amplitude, the greater the risk for clinically significant hemolysis, depending on the ambient temperature.

  • Cold agglutinins bind red cells in the superficial vessels impeding capillary flow, producing acrocyanosis.

  • Hemolysis is dependent on the antibody's ability to bind complement to the red cell membrane; concurrent agglutination is not required ...

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