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 end threats. In general, immune reactions prevent the onset of disease and aid in the recovery of the individual, but at other times, they target non-hazardous substances and cause tissue damage of varying severity.

These are known allergies or, more precisely, hypersensitivity reactions. This “immune mismatch” is a growing concern globally, as the World Health Organization (WHO) estimates that by 2050 about half of the world’s population will suffer from some form of disease. alcohol-related disorder. Today, rhinitis affects 25% of humans, no more and no less.

In countries like Spain, we see that the rates of allergies in children are increasing by 2% per year. This translates to an approximate 100% increase in queries every few years. All of this data highlights the importance of immune hypersensitivity today, but do you know what those reactions are? Otherwise don’t worry, because here you will know the 4 types of hypersensitivity.

    What is hypersensitivity?

    First of all, it should be noted that immune system disorders can be classified into the following groups:

    • States of hypersensitivity.
    • Auto-immunity.
    • Conditions of congenital or acquired impairment.

    It is in the first variant that we will focus. Classically, it is defined as hypersensitivity to an exaggerated immune response which produces a medical condition resulting in disturbance, discomfort and, on rare occasions, sudden death.

    This event has a lot in common with autoimmunity, as it is clinically defined (according to medical specialists) as the excessive or inadequate immune response to environmental antigens, usually non-pathogenic, which cause inflammation of the body. tissues and organ dysfunction.

    Types of hypersensitivity

    Hypersensitivity can be distinguished into 4 types, depending on the components of the immune system causing the response.. We explain each of these mechanisms below by following the Gell and Coombs scale, the most well-known of all at the clinical and epidemiological level. Let’s do this.

    1. Immediate hypersensitivity

    To understand all the terminological conglomerate that we are going to throw you in the following lines, it is necessary to consolidate certain knowledge. For example, it is essential to know that an antibody or an immunoglobulin (Ig) is a type of protein circulating in the blood, which “marks” possible pathogens, binding to its antigen (Ag). Antibodies have a typical I-form 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.

    Well. Having said that, we can say that in case of immediate hypersensitivity, basophilic leukocytes and mast cells bind to IgE antibodies against certain antigens in the membranes of these cells.

    After a period of sensitization (a first contact with the allergen), the “warning” cells secrete pharmacological components such as histamine, leukotriene and prostaglandins, the immediate effect is vasodilation and muscle contraction. smooth. This is an immediate response, the symptoms depend very much on the form of entry of the antigen, the soluble dose of it and the type of response of the mast cells. These types of reactions cause atopy, anaphylaxis, and asthma.

    The severity of this clinical picture depends on whether the response is localized or systemic. When the allergic response is systemic and severe, it is a case of anaphylaxis, characterized by the following symptoms:

    • Sudden skin reactions.
    • Low blood pressure (hypotension).
    • Constriction of the airways, which may cause difficulty or inability to breathe.
    • Weak and rapid pulse.
    • Nausea, vomiting and diarrhea.
    • Loss of consciousness and fainting.

    In the event of a systemic allergic response, the only possible option is to go quickly to an emergency center or, if not, to inject epinephrine into the patient whom he must take with him and then to call the professionals. In this serious clinical picture, every second counts.

      2. Hypersensitivity to cytotoxic antibodies

      Also known as dry antibody hypersensitivity, this variant is characterized by the binding of antibodies produced by the immune system to antigens present on the surface of the cells themselves of the patient.

      In this case, the immunoglobulins (or antibodies, it’s the same) IgM and IgG are involved. These cells, which appear to be pathogenic but are not actually pathogenic, are recognized by macrophages and dendritic cells, which act as antigen presenters, encouraging B cells to generate even more antibodies for them. Thus, they end up being labeled as pathogenic cells that are not truly pathogenic, with their resulting erroneous destruction.

      A clear example is autoimmune hemolytic anemia. In it, antibodies are generated against circulating erythrocytes or red blood cells, which eventually get destroyed and cause pathologies in the patient. As you can see, it is not an allergic response, but an error of the immune system.

      However, there are many other pathologies most involved in cytotoxic antibodies. These include Goodpasture syndrome (the immune system attacks the renal glomeruli and pulmonary alveolar tissue), pemphigus (destruction of epidermal structures), immune thrombocytopenia (mistaken destruction of circulating platelets), rheumatic fever and many more. ‘other pathologies. Remember this: in this variation, the antibodies bind to cells that shouldn’t, causing their early destruction. It has nothing to do with the typical allergic response.

        3. Hypersensitivity mediated by immune complexes

        This type of hypersensitivity it is produced by the deposition of immunocomplexes in certain tissues. The binding of an antigen and an antibody (Ag-Ab) is called immunocomplexes, which are usually 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 removed, they can deposit in tissues and lead to false immune attack signals. On another side, if the dose of antigens is very high and intravenously, more immunocomplexes are produced than can be eliminated by the body, So that 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 cleared.

        Other pathologies linked to this type of hypersensitivity are glomerulonephritis (inflammation of the renal glomeruli), rheumatoid arthritis, subacute bacterial endocarditis (inflammation of the heart tissue) and systemic lupus erythematosus, among others.

        4. Delayed hypersensitivity

        Also called “cell-mediated”, this type of hypersensitivity, as the name suggests, is mediated by T lymphocytes. These lymphocytes are sensitized when they come into contact with a specific antigen, and can damage the tissue by its direct toxic effect or by the release of soluble substances (lymphokines). In short, these are late responses that occur to an antigen to which the lymphocytes were already sensitized.

          final considerations

          As you may have noticed, when we talk about allergies, we are talking about immediate hypersensitivity, mediated by IgE immunoglobulins. The rest are not allergic processes per se, because it is not that the immune system acts disproportionately due to a foreign agent, but that it mistakenly destroys the body’s own tissues. Without a doubt, hypersensitivity types 2,3 and 4 are much more pernicious and much less common than the first ones (unless we are talking about anaphylaxis).

          summary

          As we said in the first few lines, the immune system is essential for the well-being and maintenance of the body. However, like all living machines, it is prone to error and can act disproportionately against substances that are not really harmful and even kill the cellular components essential to the organism itself.

          Imagine the disaster the immune system conceives of as a threat to red blood cells or platelets. All this results in a cascade effect which manifests itself in multiple symptoms in the patient, most of them severe. Fortunately, these conditions are not common.

          Bibliographical references:

          • Anaphylaxis, Mayoclinic. Collected January 4 from https://www.mayoclinic.org/es-es/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468#:~:text=La%20anafilaxia%20es%20una%20reacci%C3% B3, the% 20picadura% 20de% 20una% 20abeja.
          • Immune Hemolytic Anemia, Medlineplus.gov. Collected January 4 from https://medlineplus.gov/spanish/ency/article/000576.htm#:~:text=La%20anemia%20hemol%C3%ADtica%20inmunitaria%20ocurre,a%20estos%20gl%C3% B3bulos% 20como% 20extra% C3% B1os.
          • Garcia Tamayo, F. (1981). The outlook for immune damage. Bowl. Med. Hosp. Baby. Mex, 865-72.
          • Rodríguez Álvarez, L., & Galofre, M. Hypersensitivity reactions.
          • Salinas, LJ (2012). Mechanisms of immune damage. Revista Mèdica Clínica Les Comtes, 23 (4), 458-463.
          • Valdez, JGR, Pereira, Q., Zini, RA and Canteros, GE (2007). Hypersensitivity reactions. Postgraduate Journal of the VIª Chair of Medicine, 167, 11-16.

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