Complement pathways are crucial components of the innate immune system, enhancing the ability to clear pathogens and damaged cells. They consist of three activation pathways—classical, lectin, and alternative—that converge to form a membrane attack complex, leading to cell lysis.

Complement Pathways

Innate Immune System

Pathogen clearance refers to the process by which the immune system identifies, attacks, and removes pathogens from the body to restore health. Effective pathogen clearance is critical for preventing infections and maintaining homeostasis, and it involves a complex interplay of innate and adaptive immune responses.

Pathogen Clearance

Damaged cells

Activation pathways

The classical pathway is one of the three pathways that activate the complement system, an essential part of the immune response, and is triggered by antibodies bound to antigens on the surface of pathogens. This pathway leads to a cascade of proteolytic events resulting in the formation of the membrane attack complex, opsonization, and recruitment of inflammatory cells to eliminate the pathogen.

Classical Pathway

The lectin pathway is a component of the innate immune system that activates the complement system through the binding of mannose-binding lectin (MBL) to pathogen surfaces. This pathway plays a crucial role in the body's first line of defense against infections by enhancing phagocytosis and promoting inflammation.

Lectin Pathway

The alternative pathway is a component of the innate immune system that activates the complement system without the need for antibodies, providing a rapid defense mechanism against pathogens. It is triggered by the spontaneous hydrolysis of complement component C3 and is regulated by various factors to prevent damage to host cells.

Alternative Pathway

The Membrane Attack Complex (MAC) is a crucial component of the immune system's complement pathway, forming a pore in the cell membrane of target pathogens to induce cell lysis and death. It is formed by the assembly of complement proteins C5b, C6, C7, C8, and multiple C9 molecules, creating a transmembrane channel that disrupts the integrity of the pathogen's membrane.

Membrane Attack Complex

Cell lysis is the process of breaking down the cell membrane to release the cell's contents, often used in laboratory settings to extract proteins, nucleic acids, or other cellular components. This process can be achieved through mechanical, chemical, or enzymatic methods, each tailored to the specific type of cell and the desired outcome of the lysis.

Concepts

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