Antigen systems and classification of agglutinins
In practical surgery and transfusiology, specific antigen and antibody systems play a crucial role. Special attention is paid to the Ym system, which is closely associated with immunoglobulins (Ig) and has direct clinical significance. At the same time, plasma antigens are usually not taken into account in routine blood transfusion practice.
The key participants in immunological reactions are antibodies, or agglutinins. They are generally divided into two large groups depending on their origin and temperature preferences:
- Congenital (natural) agglutinins. These include permanent $\alpha$ and $\beta$ antibodies. They are cold antibodies because they exhibit maximum activity and function at normal room temperature.
- Acquired (immune) agglutinins. These antibodies are non-permanent. They are produced by the body exclusively as a defensive response to the introduction of foreign antigens (the most prominent example being the Rh factor). Unlike natural ones, they are warm antibodies, meaning they function fully at human body temperature.
Mechanism of interaction and phases of erythrocyte destruction
The main cause of immunological incompatibility is the encounter of identical structures in the bloodstream. We are talking about combinations such as antigen A and antibody $\alpha$, antigen B and antibody $\beta$, or the Rh antigen and specific anti-Rh antibodies. A prerequisite for the development of a clinically significant reaction is a sufficient quantity (titer) of these antibodies in the blood serum.
The process of the antigen-antibody complex conflict proceeds in two consecutive phases:
- Agglutination (first phase). Specific antibodies find their targets and firmly attach to the blood cell membrane. As a result, the formed elements begin to clump together.
- Hemolysis (second phase). Plasma complement joins the formed immune complex. Its activation leads to total lysis (destruction) of the erythrocyte cell membrane.
Ottenberg's rule and the concept of universal groups
The foundation of classical transfusiology is Ottenberg's rule. The essence of the rule is as follows: during blood transfusion, it is specifically the red blood cells of the donor blood that agglutinate (clump).
The mechanism behind this phenomenon lies in the dilution effect. When donor agglutinins enter the body, they are diluted manifold by the recipient's blood. Their concentration drops sharply and becomes insufficient to agglutinate the recipient's red blood cells.
It is precisely on this principle that the practical application of universal blood groups is based:
- Group 0(I) acts as a universal donor because its red blood cells completely lack agglutinogens.
- Group AB(IV) is a universal recipient because its plasma lacks agglutinins capable of attacking foreign blood.
Limitations of the rule and consequences of massive transfusion
Despite the logic of the concept, Ottenberg's rule has extremely strict limitations associated with so-called massive transfusion.
When a large amount of donor blood is transfused, the physiological protective mechanism of the dilution effect ceases to work. Donor agglutinins simply do not have time to be diluted in the recipient's plasma to a safe level. As a result, they maintain a high concentration and may begin to agglutinate the recipient's own red blood cells.
In this regard, a clear limit has been established: Ottenberg's rule is safe and applicable only in cases where the volume of transfused donor blood is no more than 500 ml.
Briefly: answers to topical questions
What clinical symptoms are characteristic of transfusion shock during incompatible blood transfusion?
Clinical symptoms of transfusion shock depend on the period of its course and the degree of decrease in systolic blood pressure (SBP). Symptoms may appear after the administration of as little as 10–30 ml of incompatible blood.
- Actual shock — accompanied by a drop in SBP (grade I — down to 90 mm Hg, grade II — down to 80–70 mm Hg, grade III — below 70 mm Hg).
- Oliguria and anuria period — characterized by decreased diuresis and the development of uremia.
- Diuresis recovery period — manifested by polyuria and decreased azotemia.
What minor erythrocyte antigen systems, besides ABO and Rh, are taken into account during blood transfusion?
During blood transfusion, in addition to the ABO systems and the Rh factor, minor red blood cell antigen systems are taken into account:
- Kell;
- Duffy;
- Kidd;
- MNS;
- Lewis;
- Lutheran.
Subgroups and antigens A-1, A-2, C, c, E, and e are also determined.
What specific complications develop in massive transfusion syndrome?
When a large amount of blood is transfused, the following may develop:
- Agglutination of the recipient's red blood cells — because donor agglutinins do not have time to be diluted in the recipient's blood.
- Citrate intoxication — due to the binding of calcium ions by citrate, leading to hypocalcemia. It manifests as tremors, convulsions, decreased blood pressure, and arrhythmia; in severe cases, pupil dilation, pulmonary edema, and cerebral edema are possible.
The universal donor is "empty" (no agglutinogens), the universal recipient is "clean" (no agglutinins). The rule works until you pour "half a liter" (500 ml limit).
Class and exam questions
What is the main cause of blood incompatibility?
Incompatibility occurs when a matching antigen and antibody meet (e.g., A and $\alpha$, Rh antigen and anti-Rh antibodies), if a sufficient titer of antibodies is present in the serum.
How do congenital agglutinins differ from acquired ones?
Congenital ones ($\alpha$, $\beta$) are permanent and cold (acting at room temperature). Acquired ones are formed in response to foreign antigens and are warm (acting at body temperature).
What is the role of plasma complement in incompatibility?
Plasma complement binds to the antigen-antibody complex during the second phase of the reaction (after agglutination), which causes lysis of the erythrocyte membrane and leads to hemolysis.
At what blood volume does Ottenberg's rule cease to apply?
The rule is applicable only when transfusing up to 500 ml of blood. At a larger volume (massive transfusion), donor agglutinins do not have time to dilute and cause clumping of the recipient's red blood cells.
What else to study on this topic
- Clinical significance of the Ym system and its relationship with immunoglobulins.
- Detailed mechanism of erythrocyte membrane lysis under the action of plasma complement.
- Features of immune antibody production in response to the introduction of the Rh factor.
- Pathophysiology of massive transfusion and mechanisms of overcoming the dilution effect.
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