Phagocytes

Phagocytes

Introduction

Phagocytes are a crucial component of the body's immune system, responsible for recognising and destroying harmful pathogens. These specialised white blood cells play a vital role in defending the body against infections. In this section, we will explore the functions and mechanisms of phagocytes.

Phagocytosis: Engulfing Pathogens

• Phagocytosis is the process by which phagocytes engulf and digest pathogens, such as bacteria, viruses, and fungi.
• The term 'phagocyte' comes from the Greek words 'phago,' meaning 'to eat,' and 'cyte,' meaning 'cell,' highlighting their role in devouring foreign invaders.

Key Steps in Phagocytosis

1. Recognition

Phagocytes have specialised receptors that can identify molecules found on the surface of pathogens. These receptors allow phagocytes to recognise foreign invaders as threats.

2. Engulfment

Once a phagocyte has recognised a pathogen, it extends its cell membrane to envelop the invader. The pathogen becomes enclosed within a membrane-bound vesicle called a phagosome.

3. Digestion

Within the phagosome, the phagocyte deploys digestive enzymes contained in lysosomes. These enzymes break down the pathogen, destroying its molecular components.

4. Elimination

After digestion, the remnants of the pathogen are expelled from the phagocyte in a process known as exocytosis.

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Phagocytes

Types of Phagocytes

There are two main types of phagocytes in the body:

Neutrophils

These are the most abundant white blood cells and are often the first to arrive at the site of infection. They are highly effective at phagocytosis and play a critical role in the initial response to infections.

Macrophages

Macrophages are larger phagocytes that patrol tissues and organs, actively seeking out and engulfing pathogens. They also play a role in presenting pathogen fragments to other immune cells to initiate a more specific immune response.

Cytokine Release

• Phagocytes not only engage in phagocytosis but also release signalling molecules called cytokines.
• Cytokines serve as chemical messengers that attract more phagocytes to the site of infection. This amplifies the immune response and helps recruit additional immune cells to combat the invading pathogens.

The Role of Phagocytes in Immunity

• Phagocytes are a crucial part of the innate immune system, providing immediate defence against a wide range of pathogens.
• While they do not possess the specificity of adaptive immunity (which involves antibodies and T cells), phagocytes serve as the body's first line of defence and are essential for preventing the spread of infections.
• Phagocytes also play a role in initiating adaptive immune responses by presenting pathogen fragments to T cells, which triggers a more targeted and long-lasting immune reaction.

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Phagocytes

Summary

Phagocytes are specialised white blood cells that recognise and destroy pathogens through the process of phagocytosis. They engulf invaders, digest them with lysosomal enzymes, and eliminate the remnants. Neutrophils and macrophages are the primary types of phagocytes, with neutrophils being the first responders to infections. Phagocytes also release cytokines to attract more immune cells to the site of infection, amplifying the immune response. While phagocytes are part of the innate immune system, they play a crucial role in initiating adaptive immunity and are essential for the body's defence against infections.