Cross immunity

People, the one Cross immunity are immune to a homologous (similar) further pathogen when they come into contact with a pathogen. Are synonyms acquired immunity and Cross reaction.

What is cross immunity?

Cross immunity is based on a specific immune response against a certain antigen (pathogen). However, the ability to fight off the pathogen must first be acquired through initial contact with this antigen. The immune response to the pathogen is not immediate, but rather delayed in the form of a specific antigen-antibody reaction.

The cross reaction only intervenes when the unspecific (natural) immune system fails or the organism is repeatedly attacked. Cross immunity takes a few days or weeks to take effect. With specific accuracy, it is only directed against an attacker (pathogen) and only reacts after renewed contact with the antigen.

Function & task

The natural defense system in the form of so-called phagocytes, which appear as macrophages, neutrophilic granulocytes and monocytes, takes care of pathogens that have managed to penetrate the organism. It also includes proteins that are soluble in the blood and have their own defenses. It is a cellular defense front that is activated and attracted by chemical messengers. She is always the first at the scene of wounds and sources of infection.

This natural defense is also called unspecific defense, because it is not directed against certain antigens like the innate immunity or the acquired immunity (cross immunity), but immediately devours every potentially threatening, unknown and foreign pathogen. An analysis of the attacker does not take place, just as little as the immune cells remember the pathogen type. They surround it with phagocytes and "throw" it out.

Fungi, viruses, mycobacteria, bacteria and parasites are the uninvited lodgers that keep the immune system active on a regular basis. Often they pose a health threat and need to be eliminated.

The anatomical barriers are the outer boundaries such as skin, mucous membrane, cilia, nose nose or the bronchial mucous membrane, which ward off the worst attacks from the outside. They render germs harmless. If these anatomical barriers are irritated or injured, pathogens can easily penetrate the weakened organism.

The cross immunity is directed not only against the original antigen, but also against other, related antigens. If a person falls ill with a bacterial infection, cross immunity against other related bacteria is possible. The sick person is no longer infected with the bacterial secondary disease, as the cross-reaction makes them immune to the causative pathogens. The body's own defense system develops a resistance to a new disease.

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Illnesses & ailments

Since the immune system often reaches its natural limits, the organism activates the intelligent defense system. B-lymphocytes, which form in the bone marrow, take control. They collect in the spleen and lymph nodes and at this point form antibodies against the invading pathogens. The T lymphocytes mature in the thymus and together with the B cells form the “specific defense”. This type of immune system also includes cross immunity, because it defends itself against individual, specific pathogens.

The cross-reaction usually defends itself against homologous (similar) pathogens, but in isolated cases it can also act against heterologous (different) antigens. The special thing about this process is that the immune system remembers the nature of the attacking pathogen types. In the event of a repeated infection, the organism can react effectively and quickly. However, this form of the acquired defense does not start immediately, but takes a few days or weeks until it unfolds its full effect, as a learning process takes place in the body. This immune protection is maintained by memory cells (immunological memory) for years or even a lifetime.

After this learned process and its implementation, the immune system can become stronger. Vaccinations are also based on this principle. When the vaccine is given, the organism is led to believe that there is an infection with a special germ, since the external nature of the vaccine is very similar to the pathogen causing the infection. However, it is designed in such a way that it does not lead to illness.

The body creates antibodies and remembers them. If an actual infection occurs, the organism immediately uses its entire arsenal of antibodies to fight the invading pathogen. However, the memory of the immune cells decreases over time, so that a new vaccination is necessary. Three vaccinations are required against tetanus, while a single vaccination is sufficient for influenza.

Humans are regularly surrounded by viruses and bacteria and they almost always try to penetrate the body's own defense barrier, but mostly without success. If the body's own defense system does not function as it should, this can lead to many complaints and illnesses such as cough, hay fever, various allergies, fever and a large number of different infectious diseases. A protective effect achieved through antibiosis can lead to an incorrect colonization with resistant pathogens if certain, useful bacteria are suppressed or killed by the administration of antibiotics. Fungi and staphylococci then spread unhindered and become pathogenic.

The various infectious diseases immunize in different ways. Measles induces lifelong immunity in many people, while it cannot be ruled out that people who suffer from scarlet fever may develop it a second time in their lifetime. In dengue fever, the organism develops protective antibodies against the infecting subtype, but in the event of renewed infection with a dengue virus of the three other subtypes, these have an intensifying effect on the course of the disease and increase the pathogenicity. This infectious disease is an example that cross-immunity through initial contact with a virus does not always immunize the organism against other, similar types.