Complement and Phagocytosis - Vocabulary

Vocabulary flashcards based on the lecture notes about Complement and Phagocytosis.

Complement Factors

Heat-labile proteins found in blood and tissue fluids, mainly produced by the liver, that enhance the ability of antibodies and phagocytic cells to clear microbes.

Complement System

A part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes, promote inflammation, and attack the pathogen's cell membrane.

Complement Activation Cascade

The sequential manner in which complement factors activate each other, where the product of one reaction forms the enzyme for the next.

Classical Pathway

A complement activation pathway that is initiated by antigen-antibody complexes (immune complexes) activating the C1-complex.

Lectin Pathway

A complement activation pathway that is activated when mannose-binding lectin (MBL) binds to mannose residues on microbial surfaces.

Alternative Pathway

A complement activation pathway that is continuously activated at a low level due to spontaneous C3 hydrolysis.

C3-convertase

An enzyme complex that cleaves C3 into C3a and C3b.

C5-convertase

An enzyme complex that cleaves C5 into C5a and C5b.

Membrane Attack Complex (MAC)

A complex (C5b,6,7,8,9) that forms a hollow cylinder that becomes inserted into the target cell membrane, leading to cell lysis.

Mannose-Binding Lectin (MBL)

A plasma protein that binds to mannose residues on microbial surfaces, initiating the lectin pathway.

MASP-1 and MASP-2

MBL-associated serine proteases that are activated upon MBL binding to mannose, similar to C1r and C1s in the classical pathway.

Factor B

A complement factor that forms a complex with C3b in the alternative pathway, which is then split by factor D to form C3bBb.

Factor D

A complement factor that splits factor B when it is complexed with C3b in the alternative pathway.

Properdin (Factor P)

A complement factor that helps in the generation and stabilization of the C3 convertase in the alternative pathway.

C3b

A fragment of C3 that binds to microbial surfaces and opsonizes pathogens for phagocytosis.

C3a, C4a, and C5a

By-products of complement activation that have inflammatory effects.

Anaphylatoxins

Complement fragments (C3a, C4a, and C5a) that cause degranulation of mast cells and basophils, leading to inflammation.

CD59 (Protectin)

A regulatory protein that inhibits C9 polymerization on host cells during the formation of the membrane attack complex.

Opsonization

The process by which a pathogen is coated with C3b, facilitating its phagocytosis by phagocytic cells.

Immune Complex Clearance

The removal of soluble immune complexes from the circulation by erythrocytes with C3b receptors transporting them to organs rich in fixed phagocytes.

Phagocytosis

The process by which phagocytes engulf and ingest microorganisms or other cells and foreign particles.

Neutrophils

A type of phagocyte that is a primary component of the innate immune system.

Monocytes/Macrophages

A type of phagocyte that can phagocytose pathogens and present antigens to T cells.

Dendritic Cells

A type of antigen-presenting cell and phagocyte that initiates adaptive immune responses.

Oxidative Killing

A phagocyte killing mechanism that involves the production of reactive oxygen intermediates.

Non-Oxidative Killing

A phagocyte killing mechanism that involves the use of enzymes and antimicrobial peptides, such as lysozyme and defensins.

Reactive Oxygen Intermediates

Toxic oxygen-based molecules produced by phagocytes to kill ingested microbes.

Reactive Nitrogen Intermediates

Nitric oxide-related molecules produced by phagocytes that contribute to antimicrobial activity.

Phagolysosome

The structure that results from the fusion of a phagosome and a lysosome; pathogen destruction occurs here.

Lysozyme

An enzyme present in phagocytes that degrades bacterial peptidoglycan, contributing to non-oxidative killing.

Defensins

Antimicrobial peptides produced by phagocytes that disrupt microbial membranes.

Lactoferrin

A protein produced by phagocytes that binds iron, limiting microbial growth.

Proteases

Enzymes produced by phagocytes that degrade microbial proteins.

Oxidative Burst

A rapid release of reactive oxygen species (ROS) from phagocytes.

Classical Pathway C3 Convertase

C4b2a complex, which promotes cleavage of C3 into C3a and C3b.

Classical Pathway C5 Convertase

C4b2b3b complex, which promotes cleavage of C5 into C5a and C5b.

Alternative Pathway C3 Convertase

C3bBb, which cleaves more C3.

MBL Pathway Activation

Binding of Mannose-Binding Lectin (MBL) to mannose residues on microbial surfaces.

C1-complex

Composed of 3 components C1q,C1r,C1s; which activates C4 and C2.

Ag-Ab Complex

Activation signal for the Classis Pathway