The Complement Cascade & Other Functions of Complement

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Immunology

Summary

The Complement Cascade is a complex system of proteins with the key role of destroying pathogens, signalling to other immune cells about the presence of invaders, and aiding in their destruction. The three main functions of the Complement are: To create a membrane attack complex (MAC) which creates pores in cells resulting in lysis, to opsonize bacteria which tags them for phagocytosis, and to recruit other cells to assist in destroying the pathogen. Proteases, known as convertases, facilitate these processes by cleaving successive proteins in a cascade-like manner. Complement activation can occur through three routes, the classical pathway, the alternative pathway, and the mannose-binding lectin pathway, which all lead to a common Complement pathway. Two subunits, C3a and C3b, are derived from the cleavage of protein C3. Depending on their path, subunit C3b can tag a microbe for opsonization or mix with other proteins to form C5 convertase. Eventually, C5b fuses with proteins C6-C9 to formulate the MAC. In contrast, the 'A' subunits, namely C3a and C5a, function as chemoattractants for other cells of the immune system, thereby bolstering the fight against bacteria.

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FAQs

What is the role of Neutrophils among other White Blood Cells in the immune system?

Neutrophils are the most abundant type of white blood cells and are crucial to the human immune system. They serve as the body's first responders to combat infection. These cells are capable of phagocytosis, a process where they consume and destroy harmful bacteria and fungi entering the body before they can cause illness.

Why are Neutrophils often referred to as first responders in the event of an infection?

Neutrophils are referred to as first responders due to their rapid response to foreign pathogens that enter the body. They are the first type of white blood cells to travel to the site of an infection, migrating quickly in response to chemical signals such as chemokines. Here, they help fight infections by phagocytosing, or engulfing, the invading microorganisms.

How do Neutrophils migrate to the site of infection?

The migration process of neutrophils is guided by a range of chemical signals including chemokines and cytokines. These molecules are released from the site of infection and create a chemical gradient that neutrophils follow, a process known as chemotaxis. This allows the cells to efficiently find and destroy foreign pathogens.

What is the role of chemokines in the function of Neutrophils?

Chemokines play a crucial role in the functionality of neutrophils. They are a type of cytokine, or signaling protein, that guides the migration of cells. When an infection occurs, chemokines are released from the site and helps guide neutrophils towards the area of infection, promoting swift response and aiding in effective immune response.

What is the difference between Neutrophils and Leukocytes?

All neutrophils are leukocytes, but not all leukocytes are neutrophils. The term 'leukocyte' refers to all white blood cells in the body, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils. However, neutrophils make up the majority of leukocytes and are the first to respond to infections, hence their importance in the body's immune response.

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