Type IV Hypersensitivity

Adaptive immunity, which relies on a variety of responses to work, maybe involved in a variety of issues when it comes to tissue injury and disease. It can protect the body from harmful infections, but it can also be involved in cases where the body's immune system overreacts, causing tissue damage. Hypersensitivity reactions are the collective term for these disorders.

A variety of factors can cause hypersensitivity reactions. For starters, our immune system may respond to the functioning cells in our bodies. The immune system uses a screening mechanism in which self-detecting immune cells are removed from circulation in normal circumstances. However, in some people, this function may be absent.

In the presence of a microbe, hypersensitivity may also be triggered. The attempts to neutralize the microorganism are exaggerated in this case. This can result in the destruction of cells, tissues, and structures near the invasion site. When the microorganism is persistent, this process is most noticeable.

Antigens in the environment can also contribute to tissue degradation as a result of the immune response. In the presence of an allergen from the environment, a specific antibody (immunoglobulin E or IgE) is formed in some people, resulting in an allergic reaction.

This article will study Type IV Hypersensitivity/T Cell-Mediated Hypersensitivity and type 4 hypersensitivity treatment in detail.

Type IV Hypersensitivity/T Cell-Mediated Hypersensitivity

Type 4 Allergic Reaction due to helper T lymphocytes

Type 4 hypersensitivity reactions are also known as type 4 delayed hypersensitivity characterized by a delayed response mediated by either helper or cytotoxic T cells, as the name suggests. The helper T cells are normally involved in the majority of cases of hypersensitivity.

• This subset of T lymphocytes does not target pathogens directly. Instead, it develops interleukins and other cytokines that help other immunologically active cells proliferate. The TH1 and TH17 types of helper T cells are involved in type IV hypersensitivity.

• When cells that display antigens, such as dendritic cells and macrophages, release certain cytokines, helper T cells become activated. These cytokines cause TH1 or TH17 cells to proliferate. These effector cells enter the circulation after being developed and act as long-term guardians against potential pathogens.

• Since damaged interleukins take hours to days to accumulate in the circulation, the effects of this form of the mechanism are delayed. The interleukins that are produced attract cells like neutrophils and macrophages, which can phagocytose or destroy pathogens in the region. 

Type 4 Hypersensitivity Reaction Leads to -

1. Tuberculin reaction

2. Contact dermatitis

3. Some drug reactions

4. Rheumatoid arthritis-RA is a long-term condition that causes inflammation and pain in the joints. Flares or exacerbations are times when these symptoms and signs appear. Periods of remission, on the other hand, are when symptoms fully vanish.

5. Although RA symptoms can affect a number of organs in the body, the symptoms of RA in the joints include joint pain, joint swelling, joint stiffness and loss of joint function and deformities

6. Multiple sclerosis-Multiple sclerosis is characterized as the presence of multiple indurations (sclerosis) in the central nervous system (CNS). MS is a chronic, immune-mediated, inflammatory CNS disease that causes physical disabilities by destroying the myelin sheath and nerve cells to varying degrees.

7. Inflammatory bowel disease-The inflammatory disease ulcerative colitis (UC) affects the mucosal surface of the colon and is idiopathic. It, like Crohn's disease, is an inflammatory bowel disease (IBD). The rectum is often involved, and inflammation will spread through the colon proximally. Diffuse friability, erosions with bleeding, and haustra loss are all evident on endoscopy in ulcerative colitis.

8.  Inflammatory diseases

Type 4 Hypersensitivity Due to Cytotoxic T Cell

Cytotoxic T cells, unlike helper T cells, kill the cells that carry the triggering antigen directly. As a result, this subtype is particularly effective against viral and parasitic infections where the pathogen is present intracellularly.

These cells cause harm to the microbe by releasing molecules and complexes that harm it. Unfortunately, these compounds are not exclusive to offending agents and may damage healthy tissues in the surrounding area. The following are examples of cytotoxic T lymphocyte-mediated hypersensitivity:

1. Liver damage during viral hepatitis

2. Organ graft rejection

Did You Know?

Adaptive immunity employs a more complex group of receptors to detect a wider variety of microbes that may cause disease in the body. Lymphocytes and antibodies are the most important components of this group. Humoral immunity and cell-mediated immunity are the two forms of immunity in this group.

The humoral immunity is maintained by antibodies formed by B lymphocytes. These highly specialized proteins bind to target microorganisms and either neutralize, eliminate, or present them to more effective effector mechanisms.

T lymphocytes, on the other hand, are mainly responsible for cell-mediated immunity, which involves phagocytosis and the destruction of microorganisms and infected cells. Since antibodies are ineffective at neutralizing and killing intracellular microorganisms including parasites and viruses, T lymphocytes may be a better option.