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Normally, individuals carry antibodies (Abs) against A or B antigens (Ags) lacking from their particular red blood cells (RBCs). This foreseen complimentary affiliation allows serological grouping in conjunction to ABO grouping analysis.
The immunological compositions that confer A/B characteristics to fragments of the red blood cell membrane also prevail in other biological matter, most prominently in prokaryotic cell walls. Prokaryotes themselves are prevalent throughout the world and it looks like their inhabitancy within intestinal flora, dirt, foodstuff and other broadly available entities establish a continual feature of all individuals to A and B-similar Ags. Immunologically competent individuals are able to react to surrounding Ags by stimulating antibody production to Ags not present on their RBCs. As a result, anti-A appears in serum of group O and B individuals, whereas anti-B appears in serum of group O and A individuals. Group AB individuals carry both Ags on their RBCs and therefore do not produce any A or B antibodies.
Anti-A/B production is normally initiated after a couple of months proceeding birth. Production of Abs stay fairly consistent until adulthood. In the aged, anti-A/B levels may be lesser compared to that seen in teenagers. Due to antibody production generally taking place right after birth, analysis of neonatal or infantile sera cannot be regarded as accurate due to the fact that Abs may possibly have been attained through placental transfer of mother's IgG anti-A/B.
Abs are designed effectively of IgM molecules. Small amounts of IgG are also found in sera of group A and B individuals. However, in sera of group O individuals, IgG is the principal molecule that can easily transverse the placenta resulting in haemolytic disease of the newborn (HDN).
Both IgM and IgG immunoglobulins selectively agglutinate RBCs at room temperatures of 20-25°C or less. IgM and IgG are also potent inducers of complement at 37°C. Complement activation is marked when an incubation step at 37°C is supplemented to serum group testing. Now and then individuals or donors are seen whose sera results in the lysis of ABO-incompatible RBCs at thermal readings below 37°C. Lysis by Abs in serum grouping analysis should be questioned when a pinkish-red discolouration develops in the supernatant or with buttons, a reduction in size or absence. This lysis can be translated as a positive reaction.
The development of agglutinins in persons who do not have the respective foreign antigens on their RBCs is not fairly understood. Nevertheless small quantities of group A/B antigens are capable of entering the body thereby possibly initiating production of anti-A/anti-B agglutinins.
Blood sera from group O individuals consist of antibody molecules described as anti-A, B. These respond to A and B red cells where activity of both will not be changed by differential adsorption. Elution techniques using group A red cells to adsorb group O sera incorporate anti-A and another antibody, which responds to A and B red cells.
Anti-A of blood group B serum contains two different antibodies; anti-A and anti-A1. In direct-antibody testing, group B sera clump A1 and A2 red cells. However, after adsorption with A2 red cells, group B sera agglutinate only A1 red cells. This variance therefore looks like a quantitative issue and not a qualitative one. After yet more adsorption of blood group B sera with A2 red cells will eliminate total serum reactivity for A1 red cells. The distinct anti- A1 formed through adsorption of group B sera could be a weakened type of anti- A, which binds A1 red cells due to containing additional A antigen compared to A2 red cells. Anti-A1 lectin reagent diluted appropriately reacts only with A1 and not A2 red cells.
Whereas ABO Abs are mostly IgM, the Rh Abs are generally IgG. They are not found in nature, but are produced through immune stimulation via transfusion therapy or foetal red cells during pregnancy. The likely antibody to be produced is anti-D in Rh-negative people.
As Rh Abs are IgG, optimum binding takes place at 37°C and activity can be seen through indirect anti-globulin tests. Agglutination reaction processes can be amplified using albumin, low-ionic strength saline, ficin or polyethylene glycol.
Rh Abs have more potent activity with homozygous than heterozygous cells. I.e. anti-C will have greater reactivity on C+C+ cells than weaker C+c+ cells, which is termed dosage.
HDN and HTRs both can occur as results of different Rh Abs. However anti-D is the most likely cause of HDN. High immunogenicity of the D antigen has resulted in screening donors. An A+ person has both A and D antigens whereas A- means that the person does not have the D antigen, only A.
Anti-E is the most likely antibody to be present in Rh positive individuals due to 30% of people carrying the antigen, whereas Anti-C/Anti-c are less likely seen as a lot of individuals have the antigen.
Anti-e is known as an autoantibody making it very hard to obtain compatible blood as 98% of people have that antigen.
Anti-C, e/Anti-c, E are most of the time found together and therefore if an individual is without both C and e, plus has produced anti-C, then further testing needs to be done to check that anti-e is also not found.
The Rh Ags can elicit strong immune responses and therefore the Rh Abs can be regarded as likely markers of HTRs and neonatal haemolytic disease.
Due to the fact that the majority of blood types are predisposed by their RBC Ags, which vary by single or double amino acids, the Rh system comprises the D antigen that varies by an amino acid chain length of 35 compared to the C or c and E or e Ags. It is this variation in homology that accounts for the high immunogenicity of the Rh Ags.
Most of the Abs produced against the Rh Ags consist of the IgE form. These are able to cause substantial haemolytic transfusion reactions and HDN. Also the Rh Abs seldom bind complement and as a result red cell disintegration is bought about via phagocytosis, termed extra-vascular haemolysis.
Rh allo-antibodies are of IgM composition but are rarely produced naturally compared to the ABO system Abs that do develop naturally.