Lymphocytes

Introduction

Lymphocytes are a type of white blood cell that play a pivotal role in the specific immune response of our body. These remarkable cells are responsible for identifying and combating invading pathogens, contributing to our defence against diseases. In this section, we will delve into the world of lymphocytes, their functions, and their significance in maintaining our health.

Understanding Antigens

• Lymphocytes are highly specialised in recognising specific molecules called antigens. Antigens are typically proteins located on the surface of cells or pathogens, and they act as triggers for the immune response.

Two Distinct Types of Lymphocytes

1. B Lymphocytes (B Cells)

• B cells are known for their ability to produce antibodies in response to antigens. This production of antibodies is a crucial part of the immune system's defence mechanism.

• Antibodies, also called immunoglobulins, are Y-shaped proteins with receptor binding sites that are highly specific to particular antigens. When antibodies encounter antigens on pathogens, they form antigen-antibody complexes that inactivate the pathogens.

• The resulting antigen-antibody complexes can be efficiently eliminated by other immune cells, such as phagocytes.

2. T Lymphocytes (T Cells)

• T cells have a different function in the immune response. They are responsible for identifying and destroying infected body cells.

• When T cells encounter infected cells, they recognise the antigens of the pathogen displayed on the cell membrane. This recognition prompts T cells to initiate apoptosis, a programmed cell death mechanism, in the infected cell.

• Apoptosis leads to the death of the infected cell, and the remains are subsequently removed by phagocytes.

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Human Biology

Lymphocytes

Discriminating Self from Non-Self

• One remarkable aspect of our immune system is its ability to differentiate between the body's own cells (self-antigens) and foreign invaders (non-self-antigens).
• T lymphocytes, in particular, are adept at this discrimination, ensuring that they target only infected or abnormal cells while leaving healthy cells unharmed.

Autoimmune Diseases: When Self-Recognition Fails

• In cases where the regulation of the immune system falters, T lymphocytes may mistakenly identify self-antigens as foreign invaders. This leads to autoimmune diseases, where the immune system attacks the body's own cells.
• Examples of autoimmune diseases include type 1 diabetes and rheumatoid arthritis, both of which result from the immune system's misguided assault on its own tissues.

The Clonal Selection Theory

• Lymphocytes possess a remarkable ability to respond to specific antigens. When a lymphocyte encounters an antigen that matches its specific receptor, it undergoes repeated division, resulting in the formation of a clonal population of identical lymphocytes.
• This clonal selection theory explains how the immune system can produce a targeted and effective response to a wide range of pathogens, as each lymphocyte is tailored to recognise a specific antigen.

Hypersensitivity: When the Immune System Overreacts

• B lymphocytes can sometimes respond to harmless substances, such as pollen, with an exaggerated immune reaction. This hypersensitive response is known as an allergic reaction.
• Allergic reactions can manifest as various symptoms, ranging from mild discomfort to severe, life-threatening conditions.

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Human Biology

Lymphocytes

Summary

Lymphocytes, comprising B cells and T cells, are central players in the immune system's defence against infections. B cells produce antibodies that inactivate pathogens, while T cells identify and destroy infected body cells. These cells have the remarkable ability to recognise specific antigens, initiating a targeted immune response. Additionally, the immune system's ability to distinguish between self and non-self antigens is crucial for preventing autoimmune diseases. The clonal selection theory explains how lymphocytes respond to antigens, ensuring a tailored immune response. However, the immune system can sometimes overreact, leading to hypersensitivity reactions, such as allergies. Understanding the functions of lymphocytes provides valuable insights into the body's immune defence mechanisms.