As described above, antibodies actually serve to protect against diseases, i.e. they are part of the immune system. However, some diseases, such as cancer, cannot be fought by our immune system alone, as it is not fast and effective enough for this. For some of these diseases, many years of research have led to the discovery of antibodies that can be produced biotechnologically and then given to patients, such as cancer patients, as a medicine.
This has huge advantages. While chemo- or radiotherapy attacks the entire body and destroys all cells, including healthy cells, antibodies only act very specifically against the cancer cells. This specificity lies in the nature of antibodies.
Antibodies are proteins that are normally produced by cells of the immune system. However, before these cells of the immune system, the plasma cells, can do this, they must have come into contact with the foreign cells. In order to do this, they absorb the foreign cells, break them down and recognize superficial structures that “identify” the cells, so to speak, like an identity card.
Antibodies are then formed against these superficial structures, also called surface markers. This principle has been used in research. Cancer cells have been searched for such surface markers, which can only be found on the cancer cells, but not on the body’s own cells.
Antibodies were then formed against these markers, which can be given to patients as antibody treatment. The antibodies then bind to the cancer cells in the body and thus help the body’s own immune system to recognize and kill the malignant cells. For example, the antibody rituximab is effective against certain types of leukaemia and non-Hodgkin’s lymphoma and the antibody trastuzumab is effective against breast cancer cells and some stomach cancer cells.
In addition to these relatively “disease-specific antibodies”, there are also antibodies that, for example, inhibit the growth of new blood vessels and thus prevent the cancer from continuing to be supplied with nutrients from the blood. One such antibody would be Bevacizumab. It can be used in many different types of cancer.
Immunoglobulins IgG, IgM, IgA, IgE
The antibodies formed by the B-lymphocytes, also called immunoglobulins, can generally be divided into 5 subclasses: Immunoglobulin M (IgM), Immunoglobulin G (IgG), Immunoglobulin A (IgA), Immunoglobulin E (IgE) and Immunoglobulin D (IgD). The various antibody subclasses have different tasks in the immune system and also differ in their main location of residence (free, dissolved in blood or other body fluids and on the membrane of defence cells). IgA is mainly found in body fluids and on mucous membranes.
Important to mention here are the oral mucosa and saliva, mucosa of the respiratory tract, mucosa of the gastrointestinal tract and gastric juice and the vaginal mucosa. IgA prevents pathogens from entering the organism through mucous membranes that are not intact. This function is particularly important in the non-sterile areas of the body as well as the body orifices that are in constant contact with the environment, e.g. mouth and nose.
In addition, IgA is involved in eliminating pathogens that we ingest daily with food, liquid or breathing air. IgA is also found in breast milk. Breastfeeding therefore transmits antibodies from the mother to the child, thus ensuring the child’s immunity to pathogens without the infant coming into contact with the pathogen.
This mechanism is known as nest protection. Immunoglobulins of type D also occur almost completely free in blood plasma. They are more likely to be found bound to the membrane of B lymphocytes, where they form a kind of receptor for certain antigens, by which the B cells are stimulated to continue producing antibodies.
IgE is of particular importance in the development of allergies. IgE is produced by the B-lymphocytes on first contact with an allergen, such as the pollen in hay fever. Once IgE is formed, renewed contact with inhaled pollen leads to an allergic reaction.
The IgE stimulates mast cells containing histamine, so that the histamine is released. Depending on the strength of the reaction and the location of the allergen, the histamine causes symptoms. The symptoms of hay fever can be burning, itchy eyes, a runny, itchy nose or shortness of breath.
In the worst case, the allergic reaction can lead to an anaphylactic shock characterized by shortness of breath, swelling of the airways, drop in blood pressure as a sign of shock and unconsciousness. This is a medical emergency and requires immediate medical attention. The allergic symptoms can be alleviated by histamine blockers.
These block the receptors for histamine, so that the effect of histamine is lost after release. One of the most important side effects of histamine blockers is fatigue. Another function of IgE antibodies is to eliminate parasites.
In terms of quantity, IgG occupies the largest share among the antibodies. IgG is formed during the course of the infection, and is therefore part of the late immune response. If the IgG is present in the blood, it can be concluded that the infection is either over or just subsiding; full immunity is guaranteed by the IgG.
Because the immune system “remembers” the antibodies it produces, in the event of a reinfection with the same pathogen, the antibody can be quickly reproduced and the infection does not break out with signs of disease. The special thing about IgG is that this antibody is placenta-compatible. Thus, the unborn child can receive IgG antibodies from the mother and is immune to pathogens without coming into contact with them.
This is called nest protection. However, rhesus antibodies are also IgG antibodies and are therefore compatible with the placenta. If a rhesus-negative mother therefore has antibodies against the rhesus factor from rhesus-positive erythrocytes of the child, these antibodies can be transferred to the child in the subsequent pregnancy and destroy the child’s erythrocytes.
This leads to the decay of the erythrocytes, also known as haemolysis, which leads to anaemia in the child. The clinical picture in the infant is called Morbus haemolyticus neonatorum. In rhesus-negative mothers with a rhesus-positive child father, passive immunisation with anti-D antibodies (rhesus prophylaxis) can be carried out during pregnancy.
The IgM (immunoglobulin M) is structurally the largest antibody. It is formed in newly occurring infections and is involved in quickly eliminating pathogens and preventing their spread. IgM antibodies in the blood give an indication of a fresh infection that is currently taking place.
The IgM antibody also has a binding site for other systems of the immune system. Thus a part of the complement system, which consists of about twenty proteins and also serves to defend against infection, can bind to the antibody-antigen complex. Thus the complement system is activated.
The antibodies against a foreign blood group, which are formed, for example, during a blood transfusion with the wrong blood group, are also IgM antibodies. These lead to a reaction to the foreign blood and cause the blood to thicken (coagulate). This can have serious consequences for the person affected and can even be fatal within a very short time.
Therefore, before a blood transfusion, it is always important to ensure that the blood groups of donor and recipient match. This is ensured by the so-called “bedside test”, in which the blood of the donor is mixed with that of the recipient immediately before the transfusion and is monitored. If no reaction occurs, the blood can be transfused.