People who have cross-immunity are simultaneously immune to a homologous (similar) other pathogen upon contact with one pathogen. Synonyms are acquired immunity and cross-reactivity.
What is cross-immunity?
Cross-immunity is directed by a specific immune response against a specific antigen (pathogen). Cross-immunity is directed by a specific immune response against a specific antigen (pathogen). However, the ability to fight off the pathogen must first be acquired through initial contact with that antigen. The immune response to the pathogen is not immediate, but delayed in the form of a specific antigen-antibody reaction. The cross-reaction only intervenes when the non-specific (natural) immune system fails or the organism is repeatedly attacked. Cross-immunity takes several days or weeks to take effect. With specificity, it is directed against only one attacker (pathogen) and reacts only after renewed contact with the antigen.
Function and task
Pathogens that have succeeded in penetrating the organism are taken care of by the natural defense system in the form of so-called phagocytes, which appear as macrophages, neutrophil granulocytes and monocytes. Blood soluble proteins with their own defense system are also part of it. It is a cellular defense front activated and attracted by chemical messengers. It is always first on the scene in wounds and infection sites. This natural defense is also called nonspecific defense because it is not directed against specific antigens like innate immunity or acquired immunity (cross-immunity), but immediately eats up any potentially threatening, unknown and exogenous pathogen. An analysis of the attacker does not take place, just as the defense cells do not remember the type of pathogen. They surround it with scavenger cells and “throw” it out. Fungi, viruses, mycobacteria, bacteria and parasites are the uninvited lodgers that regularly keep the immune system active. They often pose a health threat and must be eliminated. The anatomical barriers are the outer boundaries such as skin, mucous membrane, cilia, nasal passage or bronchial mucosa, which repel the coarsest attacks from outside. They render germs harmless. If these anatomical barriers are irritated or injured, pathogens can easily penetrate the weakened organism. 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 further related bacteria is possible. The sick person is no longer infected with the bacterial secondary disease, as he is immune to the causative pathogens due to the cross-reaction. His or her body’s defense system develops a resistance to recurrence of the disease.
Diseases and ailments
As the immune system often reaches its natural limits, the organism activates the intelligent defense system. B lymphocytes, which form in the bone marrow, take over. They gather in the spleen and lymph nodes and form antibodies against the invading pathogens at this point. The T-lymphocytes mature in the thymus and together with the B-cells form the “specific defense”. This type of immunity also includes cross-immunity, because it defends against single, specific pathogens. Cross-immunity is usually directed against homologous (similar) pathogens, but in isolated cases it can also be directed against heterologous (different) antigens. The special feature of this process is that the immune system remembers the nature of the attacking pathogen types. In case of repeated infection, the organism can react effectively and quickly. However, this form of acquired defense does not kick in immediately, but takes a few days or weeks to develop its full effect, as a learning process takes place in the body. This immune protection persists through 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. With the administration of the vaccine, the organism is made to believe that there is an infection with a specific germ, since the vaccine is very similar in its external composition to the pathogen causing the infection.However, it is designed in such a way that it does not lead to disease. The body forms antibodies and remembers them. If an actual infection occurs, the organism immediately deploys its entire arsenal of defense substances to fight the invading pathogen. However, the memory of the defense cells wears off over time, so that a new vaccination is necessary. Tetanus must be vaccinated three times, while a single vaccination is sufficient for influenza. Humans are regularly surrounded by viruses and bacteria, and these almost always try to penetrate the body’s own defense barrier, but usually without success. If the body’s defense system does not function as it should, this can result in many complaints and diseases such as cough, hay fever, various allergies, fever and a large number of different infectious diseases. A protective effect achieved by antibiosis can lead to a miscolonization with resistant pathogens, when the administration of antibiotics suppresses or kills certain beneficial bacteria. Fungi and staphylococci then spread unhindered and become pathogenic. Different infectious diseases immunize in different ways. Measles produces lifelong immunity in many people, while it is not impossible that people who suffer from scarlet fever once will contract the disease a second time during their lifetime. In dengue fever, the organism develops protective antibodies against the infecting subtype, but these have a reinforcing effect on the course of the disease and increase pathogenicity in the event of a new infection with a dengue virus of the three other subtypes. This infectious disease is an example of how cross-immunity due to initial contact with one virus, does not always immunize the organism against the further similar types.
