3. Which one of the Immunoglobulins (Ig) cause type-I hypersensitive immune reaction?
(a) .IgA,
(b) .IgE,
(c) .IgG,
(d) .IgM,

Article:

Introduction

Type-I hypersensitivity reactions, commonly known as allergic reactions, are immune responses that occur when the body overreacts to harmless substances, such as pollen, dust mites, or certain foods. These reactions are primarily mediated by Immunoglobulin E (IgE), one of the five main classes of antibodies (also known as immunoglobulins) in the human body. Understanding the role of IgE in these hypersensitive responses is key to better managing conditions like allergies, asthma, and anaphylaxis.

What is Type-I Hypersensitivity?

Type-I hypersensitivity is an immediate allergic reaction that occurs within minutes of exposure to an allergen. The process begins when the body mistakenly identifies a harmless substance as a threat. This leads to an exaggerated immune response, involving IgE antibodies.

When an allergic person is exposed to an allergen for the first time, their immune system produces IgE antibodies. These IgE antibodies then bind to specialized cells called mast cells and basophils, which are present in tissues like the skin, lungs, and gastrointestinal tract. Upon subsequent exposure to the same allergen, the allergen binds to the IgE on these cells, triggering the release of various chemicals, such as histamine, which cause the symptoms of an allergic reaction.

The Role of IgE in Type-I Hypersensitivity

The correct answer to the question “Which one of the Immunoglobulins causes type-I hypersensitive immune reactions?” is:

(b) IgE

IgE plays a central role in type-I hypersensitivity reactions. Here’s how it works:

1. Initial Sensitization:
   Upon the first exposure to an allergen, the immune system of an allergic individual produces IgE antibodies specific to that allergen. These IgE antibodies then attach to mast cells and basophils in tissues.

2. Subsequent Exposure:
   During future exposures to the same allergen, the allergen binds to the IgE antibodies on the surface of mast cells and basophils, triggering the release of histamine and other chemicals.

3. Allergic Symptoms:
   The release of these chemicals leads to the typical symptoms of allergic reactions, such as itching, swelling, rashes, sneezing, and in severe cases, anaphylaxis.

Why IgE Causes Type-I Hypersensitivity

Unlike other immunoglobulins like IgG or IgM, IgE is specifically involved in the allergic response. Here’s why IgE is the main player in type-I hypersensitivity:

• IgE’s Unique Binding Properties:
  IgE has a high affinity for receptors on mast cells and basophils, allowing it to bind and sensitize these cells to allergens.

• Histamine Release:
  When an allergen triggers IgE on mast cells or basophils, it causes the release of histamine and other chemicals, which directly contribute to allergic symptoms such as inflammation, itching, and mucus production.

Other Immunoglobulins and Their Roles

While IgE is responsible for type-I hypersensitivity, other immunoglobulins have distinct roles in the immune system:

1. IgA:
   Primarily found in mucosal areas, such as the respiratory and digestive tracts, IgA protects against infections by preventing pathogens from entering the body.

2. IgG:
   The most abundant antibody in blood and extracellular fluid, IgG is involved in neutralizing pathogens and is the primary antibody used in immune memory and vaccine responses.

3. IgM:
   The first antibody produced during an immune response, IgM is primarily involved in initial immune defense against infections.

Common Conditions Caused by Type-I Hypersensitivity

Type-I hypersensitivity reactions can lead to a range of conditions, including:

1. Allergic Rhinitis (Hay Fever):
   Inflammation of the nasal passages caused by exposure to allergens like pollen or dust.

2. Asthma:
   A chronic respiratory condition that causes difficulty breathing due to airway constriction triggered by allergens.

3. Food Allergies:
   Allergic reactions to certain foods, such as peanuts or shellfish, can cause symptoms ranging from hives to severe anaphylaxis.

4. Anaphylaxis:
   A life-threatening allergic reaction that can cause swelling, difficulty breathing, and a drop in blood pressure. Anaphylaxis is often triggered by IgE-mediated reactions and requires immediate medical intervention.

Conclusion

IgE is the immunoglobulin responsible for type-I hypersensitivity reactions, which are the cause of common allergic conditions like hay fever, asthma, and food allergies. Understanding the role of IgE in these responses is crucial for diagnosing and treating allergies. For individuals suffering from these conditions, therapies that target IgE or its receptors are being developed to reduce the severity of allergic reactions and improve quality of life.

By recognizing IgE’s role in the immune system, we can better address the challenges posed by type-I hypersensitivity and enhance our ability to manage allergic diseases.