Complement

Historically complement has been an important subtopic in blood banking related to both pretransfusion testing and hemolytic processes such as autoimmune hemolytic anemias. In pretransfusion testing, detecting complement (via antiC3 in antiglobulin sera or via hemolysis caused by C9 helps to detect antigen-antibody reactions in which the complement is bound to the red cell. In autoimmunity, C3 on the cell (detected by the direct antiglobulin test using polyspecific antiglobulin serum) helps to diagnose the disease.

Today, complement remains important in diagnosing in vivo red cell sensitization via the direct antiglobulin test (DAT), but is no longer considered to be essential in pretransfusion testing. Indeed, some consider detection of complement binding in antibody screening tests to be undesirable. This is because many cold antibodies can bind C3 in vitro and cause a positive indirect antiglobulin test (IAT) width screen cells when polyspecific antiglobulin serum is used. When this happens, time and effort is spent investigating antibodies that are clinically insignificant; as well, delays occur which needlessly postphone transfusions.

To prevent detection of complement in pretransfusion screening (IATs), many laboratories use monospecific anti-IgG (as opposed to polyspecific antiglobulin serum containing both anti-IgG and anti-C3). There is a chance that very weak clinical significant antibodies that bind C3 (such as anti-Jka) may be missed if there are too few IgG molecules on the cell (standard antiglobulin tests require several 100 antibodies per red cell to produce agglutination); however, this risk is very small and antibodies this weak are unlikely to produce significant red cell destruction.

This section briefly reviews complement from a blood bank perspective.

Chemistry: a mixture of alpha-2D, gamma, and beta globulins present in all normal fresh serum (mostly beta globulins).

Biological Funcion

Role in Blood Banking

Ways To Ensure Adequate Complement Levels

Classical Cascade

Alternative (Properdin) Pathway

Enrichment activity #4

E-mail responses to Questions #1-4 and #5(a) to Pat .

  1. Using humoral immunity as a resource, what do IgA molecules receive from the epithelial cells and what is its function?

  2. Between which domains on the IgG molecule is the hinge region located?

  3. List four functions of B lymphocytes.

  4. Briefly describe 10 functions of free antibody.

  5. Visit this commercial site of Dade International .

    (a) Using the section, "Conventional Antiglobulin Reagents: REQUIRED ANTIBODY SPECIFICITY" as a resource, briefly discuss the reasons proposed by Charla Issitt for why unwanted positive reactions may sometimes occur when using polyspecfic antiglobulin serum for indirect antiglobulin tests.

    (b) After reading all of Issitt's paper, send e-mail to the class mailing list that explains your opinion of the purpose of Issitt's paper at the Dade site.

    (c) Also send a comment to the class mailing list in reply to another class member's opinions.

Complement