4 Most SAQ’s of Immune System Chapter in Inter 2nd Year Zoology (TS/AP)

4 Marks

SAQ-1 : Write short notes on B-cells.

Introduction

B-cells, or B lymphocytes, are a crucial type of white blood cell that play a significant role in the body’s immune system. They are specifically tasked with the production of antibodies to fight off invading pathogens, such as viruses and bacteria.

Origin and Maturation

B-cells are originally formed in the bone marrow of adult mammals and in the liver of fetuses. Once matured, these B-cells carry various types of antibodies on their plasma membrane. These antibodies have the unique ability to bind to antigens, or foreign substances, in the body. Because of this, mature B-cells are often referred to as immune competent B cells.

Function and Transformation

Mature B-cells, or MBC cells, then travel to secondary lymphoid organs where they further develop into functional immune cells. These functional immune cells can transform into two different types of cells: long-lived memory cells and effector plasma cells.

Role of Plasma and Memory Cells

Plasma cells are responsible for producing specific antibodies that can recognize and neutralize the invading antigens. Memory B-cells, on the other hand, serve an important function in the immune system’s “memory.” They store information about specific antigens and enable a quick and robust immune response if the same antigen is encountered again in the future.

Summary

In conclusion, B-cells, as an integral part of the immune system, play a pivotal role in defending the body against infections. They achieve this by producing antibodies, remembering past invaders, and mounting a rapid response upon re-exposure to familiar antigens.

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SAQ-2 : Write short notes on Immunoglobulins.

Introduction

Immunoglobulins, also known as antibodies, are specialized proteins produced by B lymphocytes in response to invading pathogens in the body. These antibodies are unique and specific to the antigens present on the pathogens.

Types of Antibodies

There are two main types of antibodies: free antibodies and surface antibodies.

1. Free, or circulating, antibodies are found in blood and lymph. They move around the body to detect and neutralize pathogens.
2. Surface antibodies, in contrast, are located on the surface of B cells and memory cells, ready to engage with antigens upon contact.

Structure of Antibodies

An antibody molecule is shaped like a ‘Y’ and consists of four polypeptide chains.

1. Two of these chains are long, identical, and are called heavy chains (H). The other two are shorter and are known as light chains (L), often represented as H2L2.
2. These chains are held together by disulfide bonds.

Two Ends of Antibodies

1. One end of the antibody, known as the Fab end, binds to the antigen.
2. The other end, called the Fc end, can attach to B-cells.

Different Classes of Antibodies

There are five classes of antibodies, which vary based on their structure and function. These classes are IgD, IgE, IgG, IgA, and IgM.

Summary

In summary, immunoglobulins are essential components of the immune system, working to recognize and neutralize foreign invaders. They are produced by B lymphocytes and can be either circulating or attached to the surface of cells. With their unique ‘Y’ shaped structure and their capability to bind specifically to antigens, they play a crucial role in the body’s defense mechanism.

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SAQ-3 : Explain the mechanism by which HIV multiplies and leads to AIDS.

Introduction

HIV, or Human Immunodeficiency Virus, is a virus that targets the immune system, leading to a disease called AIDS (Acquired Immunodeficiency Syndrome). It can be transmitted in several ways, including through sexual contact, blood transfusion, sharing needles, and from mother to child during birth.

1. How HIV Multiplies: Upon entering the body, HIV invades the T-helper cells, macrophages, and dendritic cells.
   • Within these cells, the single-stranded RNA (ssRNA) of HIV is used to create a ‘DNA strand‘ that is complementary to the ‘viral RNA strand‘. This process is facilitated by an enzyme called reverse transcriptase.
   • This same enzyme also assists in forming a second DNA strand, which is complementary to the first.
   • As a result, a double-stranded viral DNA is formed.
   • This viral DNA is then incorporated into the host cell’s DNA with the help of another enzyme called integrase.
   • Once incorporated, this DNA is known as a provirus.
2. Viral Particles Formation:
   • The provirus transcribes RNA that can be translated into viral proteins or particles.
   • These viral particles are assembled to form new HIV viruses.
   • The infected human cells essentially become HIV-producing factories, constantly generating more of the virus.
3. Impact on the Body:
   • As HIV multiplies, T-helper cells are infected and destroyed. This leads to a weakened immune system.
   • The period between initial infection and the appearance of symptoms can vary widely, from a few months to up to 10 years.
4. Symptoms of AIDS: An individual with AIDS may experience repeated bouts of fever, diarrhea, and significant weight loss.

Summary

HIV multiplies within the body by invading specific cells, creating a double-stranded DNA from its RNA, and incorporating this into the host cell’s DNA. This process leads to the production of more HIV viruses, which further infect and destroy immune cells. Over time, this results in the development of AIDS, characterized by a weakened immune system and various associated symptoms.

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SAQ-4 : Describe various types of barriers of Innate Immunity.

Introduction

Innate immunity is the body’s first line of defense against diseases. It’s an inborn form of resistance that works through various barriers. These barriers include physical, physiological, cellular, and cytokine barriers.

1. Physical Barriers:
   • The skin and mucous membranes act as physical barriers.
   • The skin acts as a protective layer, preventing the entry of microorganisms.
   • Mucous membranes help to trap and eliminate microorganisms that make their way into the body.
2. Physiological Barriers:
   • Certain body secretions also form part of the physiological barriers against microbes.
   • For example, the stomach secretes hydrochloric acid (HCl), which can kill many microbes.
   • Saliva in the mouth and tears from the eyes contain an enzyme called lysozyme, which also destroys microbes.
3. Cellular Barriers:
   • There are specific cells in the body that act as cellular barriers. These include neutrophils, monocytes, killer cells in the blood, and macrophages in the tissues.
   • These cells can engulf or kill microbes, providing another layer of protection.
4. Cytokine Barriers:
   • Finally, the cytokine barrier involves proteins called cytokines that protect non-infected cells from further infection.
   • They regulate the immune response and inhibit viral replication within host cells, thus preventing the spread of infection.

Summary

Innate immunity is a natural form of protection against diseases that functions through various barriers. These include physical barriers like skin and mucous membranes, physiological barriers such as body secretions, cellular barriers including specific immune cells, and cytokine barriers involving proteins that inhibit viral replication. Each plays a critical role in preventing the entry and spread of microbes in the body.