The significance of complement in immunohematology

Analytic Reviews : Hemolytic Transfusion Reactions: A Review of Mechanisms, Sequelae, and Management

The transfusion of blood and blood products is an im portant therapeutic procedure, but it is associated with several potentially serious adverse effects. Among these complications are hemalytic reactions, which in most cases result from the interaction between donor red cell antigens and recipient plasma antibodies. Clinical mani festations and sequelae are largely determined by the physical and immunological characteristics of the anti gens and antibodies. Early recognition may be difficult in the anesthetized or intensively monitored patient. Acute hemolytic reactions are responsible for significant morbidity and mortality and may lead to life-threatening shock, disseminated intravascular coagulation, and renal failure. Fortunately, fatal hemolytic transfusion reactions are rare; they usually result from clerical errors. Proper diagnosis and management requires sound clinical judg ment, thorough laboratory investigation, and timely therapeutic intervention.

Immunoglobulin M red blood cell alloantibodies are frequently adsorbed by rabbit erythrocyte stroma

BACKGROUND

Rabbit erythrocyte stroma (RESt, Immucor) adsorption is often used to remove cold autoantibodies from patient samples to facilitate detection of underlying alloantibodies. However, reports in the literature show that adsorption of clinically significant alloantibodies can occur. A 2006 study by Storry and colleagues suggested that immunoglobulin (Ig)M antibodies are adsorbed by RESt regardless of antigen specificity. In our study, we further investigated the adsorption of IgM red blood cell alloantibodies by RESt.

STUDY DESIGN AND METHODS

A total of 12 sera containing monoclonal IgM antibodies of various specificities (anti- D, -C, -c, -E, -e, -K, -Jk(b), and -S) and titers, which were all shown to exhibit only IgM reactivity after dithiothreitol treatment, and two sera with polyclonal IgG (anti-Fy(a) and -K) were all adsorbed by RESt. Titers of unadsorbed, once-adsorbed, and twice-adsorbed IgM and IgG antibodies were determined in parallel.

RESULTS

Ten of the 12 monoclonal IgM samples showed significant (more than fourfold) reduction in titer after RESt adsorptions. Both of the polyclonal IgG samples tested showed insignificant (fourfold or less) reduction in titer.

CONCLUSIONS

RESt is known to effectively remove IgM cold autoantibodies. Our results show that monoclonal IgM alloantibodies are also frequently adsorbed by RESt with significant reduction in titer. Adsorption is variable and some IgM alloantibodies are not adsorbed. Further studies may elucidate the effect of RESt adsorption on IgG alloantibodies. Caution is needed when RESt is employed to remove interferences by cold autoantibodies in pretransfusion testing, and the risk of missed IgM alloantibodies must be considered.

Complement analysis in the 21st century

Complement analysis in the clinic is usually associated with the quantification of C3 and C4, measurement of C1-inhibitor and screening for complement activity. These analyses have been available in routine diagnostic laboratories for decades. In recent years, however, the field of complement analysis has expanded considerably, with the introduction of novel assays to detect complement activation products, and spreading still further towards genetic analysis to reveal the basis of complement deficiencies and identify mutations and polymorphisms associated with defined diseases such as atypical haemolytic uraemic syndrome and age related macular degeneration. Here we review the current status of complement analysis, including assays for the quantification of complement activity and complement activation products, together with genetic methods for the detection of deficiencies, mutations and polymorphisms. This is an area where significant developments have been made recently, paralleling the research advances into the role of complement in human disease. It is clear, however, that there is a need for consensus and standardisation of analytical methods. This will be a major challenge for the complement society in the future.

[Detection of irregular anti-erythrocyte antibodies using the indirect antiglobulin test in a low-ionic-strength medium. Immunohematology Group of the French Blood Transfusion Society]

The detection of irregular antibodies is usually performed with serum by the indirect antiglobulin test (IAT) with a polyspecific antiglobulin reagent. In a first study in 1996, we compared the results obtained with 3,264 blood samples of patients drawn with or without anticoagulant: no significant difference was observed among the 240 allo-antibodies detected and identified. In this paper we report the comparison of the results obtained by IAT on column of filtration with two kinds of reagents: polyspecific and anti-IgG antibodies. Respectively 2,927 (76 contained an antibody), and 643 (161 contained an antibody) sera of patients were tested with methods ID-Diamed and Ortho-Biovue. Titrations of 153 other antibodies were also performed with the two reagents. Results showed no significant difference using either polyspecific reagent or the anti-IgG antibodies. This study proves that it is possible to perform screening of irregular antibodies on uncoagulated blood samples. This possibility allows automation as blood typing and screening of irregular antibodies can be carried out with the same sample.

Complement in the pathophysiology and diagnosis of human diseases

Complement is a humoral effector system composed of 21 plasma proteins that was identified initially because of its cytolytic effects. In addition to cytolysis, complement has a number of different functions related to inflammatory and other host defense processes. The description of the reaction mechanism includes: (1) activation of the classical pathway through recognition of IgG and IgM antibodies by C1q, (2) activation of the alternative pathway which is usually achieved without participation of immunoglobulins, (3) generation of proteolytic enzymes composed of heteropolymers that cleave certain precursor proteins, (4) formation of the membrane attack complex (MAC), and (5) participation of control mechanisms. Methodologies for studying protein concentration and functional activities of complement components include not only the classical hemolytic techniques but also the extremely sensitive new radioimmunoassays and enzyme immunoassays for measuring the products of complement activation that are generated in vivo. Examples of genetically controlled complement deficiencies have been published for most complement components. The symptomatology of some of these patients serves to emphasize the protective role of complement. Acquired deficiencies are significant not only as laboratory aids in diagnosis and to evaluate the course of certain diseases, but also to indicate possible pathogenic disease mechanisms. Recently, it has been recognized that the complement proteins with genes located in the HLA region are polymorphic. Certain variants of proteins C2, C4, and factor B occur with higher frequencies in certain diseases than in the general population, which appears to be of great practical importance in laboratory medicine.