The 4 Types Of Hypersensitivity, And Their Characteristics
The immune system is essential for the maintenance of complex organisms over time, as it reacts and eliminates invaders such as bacteria, parasites, viruses, foreign substances, cancer cells and triggers inflammatory responses to eliminate threats. In general, immune reactions prevent the onset of diseases and contribute to the healing of the individual, but on other occasions they target non-dangerous substances and cause tissue damage of varying severity.
We are dealing with the well-known allergies or, more specifically, hypersensitivity reactions. This “immune imbalance” is an increasingly worrying issue at a global level, since the World Health Organization (WHO) estimates that by 2050 approximately half of the world’s population will suffer from some type of allergic disorder. Today, rhinitis occurs in 25% of human beings, no more, no less.
In countries like Spain, it is observed that allergic rates in infants increase by 2% annually. This translates, approximately, to a 100% increase in consultations every few years. All these data highlight the importance of immune hypersensitivity today, but do you know what these reactions consist of? If not, don’t worry, because here you will find out the 4 types of hypersensitivity
First of all, it is necessary to note that Alterations of the immune system can be divided into the following groups:
It is the first variant that we are going to focus on. From a classical point of view, it is defined as hypersensitivity to an exaggerated immune reaction that produces a pathological condition causing disorders, discomfort and, in rare cases, sudden death
This event has much in common with autoimmunity, since it is defined from a clinical point of view (according to medical specialists) as the excessive or inadequate immune response to environmental antigens, usually non-pathogenic, that cause tissue inflammation and organ malfunction.
Types of hypersensitivity
Hypersensitivity can be distinguished into 4 types, depending on the components of the immune system that cause the response We tell you about each of these mechanisms below, following the Gell and Coombs scale, the most famous of all at a clinical and epidemiological level. Go for it.
To understand the entire terminological conglomerate that we are going to throw at you in the following lines, it is necessary to establish certain knowledge. For example, it is essential to know that an antibody or immunoglobulin (Ig) is a type of protein circulating in the blood, which “marks” possible pathogenic elements, binding to their antigen (Ag). Antibodies have a typical Y shape in their monomeric variant, with a variable fraction (Fab) and a constant fraction (Fc). The immune cells responsible for eliminating the pathogen adhere to the Fc zone of the antibody, which in turn is bound to the antigen.
Good. Having commented on this, we can say that, in immediate hypersensitivity, Basophilic leukocytes and mast cells bind IgE antibodies to certain antigens on the membranes of these cells
After a period of sensitization (a first contact with the allergen), the “warned” cells secrete pharmacological components such as histamine, leukotriene and prostaglandins, whose immediate effect is vasodilation and smooth muscle contraction. It is an immediate response, the symptoms of which depend quite a bit on the way the antigen enters, its soluble dose and the type of mast cell response. These types of reactions cause atopy, anaphylaxis and asthma.
The severity of this clinical condition depends on whether the response is localized or systemic When the allergic response is systemic and severe, we are faced with a case of anaphylaxis, characterized by the following symptoms:
In the event of a systemic allergic response, the only possible option is to go quickly to an emergency center or, failing that, give the patient the epinephrine injection that they should carry with them and then call medical professionals. In this serious clinical condition, every second counts.
2. Hypersensitivity due to cytotoxic antibodies
Also known as plain antibody hypersensitivity, this variant is characterized by the binding of antibodies produced by the immune system to antigens present on the surfaces of the cells themselves of the patient.
In this case, the immunoglobulins (or antibodies, it is the same thing) IgM and IgG are involved. These cells, which appear pathogenic but in reality are not, are recognized by macrophages and dendritic cells, which act as antigen presenters, encouraging B lymphocytes to generate even more antibodies for them. Thus, cells that really are not pathogenic end up being identified, with their consequent erroneous destruction.
A clear example is autoimmune hemolytic anemia In it, antibodies are generated against circulating erythrocytes or red blood cells, which end up being destroyed and causing pathologies in the patient. As you will see, this is not an allergic response, but rather a failure of the immune system.
Even so, there are many other pathologies mediated by cytotoxic antibodies. Among them we can find Goodpasture syndrome (the immune system attacks the glomeruli of the kidney and the tissue of the lung alveoli), pemphigus (destruction of epidermal structures), immune thrombocytopenia (erroneous destruction of circulating platelets), rheumatic fever and others. many more pathologies. Remember this: in this variant, antibodies bind to cells they shouldn’t, causing their early destruction. It has nothing to do with the typical allergic response.
3. Immune complex-mediated hypersensitivity
This type of hypersensitivity It is produced by the deposition of immune complexes in certain tissues We know as immune complexes the union of an antigen and an antibody (Ag-Ac), which are normally eliminated during the development of the immune response.
Unfortunately, when the aggregations of IgM and IgG immunoglobulins with their antigens are too large to be eliminated, they can be deposited in tissues and lead to signals of erroneous immune attacks. On the other hand, If the dose of antigens is very high and intravenously, more immune complexes are produced than can be eliminated by the body, so they accumulate inside the vessels, kidneys and joints. The most common symptoms in these cases are vasculitis, nephritis and arthritis, which only appear sporadically until the immune complexes are completely eliminated.
Other pathologies related to this type of hypersensitivity are glomerulonephritis (inflammation of the glomeruli of the kidney), rheumatoid arthritis, subacute bacterial endocarditis (inflammation of the heart tissue) and systemic lupus erythematosus, among others.
4. Delayed hypersensitivity
Also known as “cell-mediated,” this type of hypersensitivity, as its name suggests, It is mediated by T lymphocyte cells These lymphocytes become sensitized when they come into contact with a specific antigen, and can damage the tissue due to their direct toxic effect or through the release of soluble substances (lymphokines). In summary, they are late responses that occur to an antigen to which the lymphocytes were already sensitized.
You may be interested: “High lymphocytes: causes, symptoms and treatment”
As you may have seen, when we talk about allergies we are referring to immediate hypersensitivity, mediated by IgE immunoglobulins. The rest are not allergic processes per se, since it is not that the immune system is acting excessively due to a foreign agent, but rather that it destroys the body’s own tissues by mistake. Without a doubt, types of hypersensitivity 2, 3 and 4 are much more harmful and much less common than the first (unless we are talking about anaphylaxis).
Summary
As we have said in the first lines, the immune system is essential for the well-being and maintenance of the body. Even so, Like all living machinery, it is subject to error, and can act excessively against substances that are not really harmful and even killing essential cellular components for the body itself.
Imagine the disaster that the immune system perceives as a threat to red blood cells or platelets. All of this translates into a cascade effect that manifests itself with multiple symptoms in the patient, most of them severe. Luckily, these conditions are not common.
Anaphylaxis, Mayoclinic. Collected on January 4 at https://www.mayoclinic.org/es-es/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468#:~:text=La%20anafilaxia%20es%20una%20reacci%C3 %B3n, the%20sting%20of%20a%20bee.
Immune hemolytic anemia, Medlineplus.gov. Collected on January 4 at https://medlineplus.gov/spanish/ency/article/000576.htm#:~:text=La%20anemia%20hemol%C3%ADtica%20inmunitaria%20occurre,a%20estos%20gl%C3 %B3hoaxes%20as%20extra%C3%B1os.
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