The Complement System Lecture Notes

Comprehensive vocabulary flashcards covering the components, functions, and three activation pathways of the complement system based on the lecture notes.

Soluble Mediators

Active substances dissolved in the plasma or the liquid portion of the blood that help fight non-self particles and are not cellular.

Complement

A heat-labile series of $18$ plasma proteins, many of which are enzymes (proteinases), that can create a hole on the surface of a cell leading to lysis.

Heat labile

A characteristic of substances, such as complement proteins, that means they can be easily destroyed by heat.

Opsonization

The covering of any pathogen so that it will be easily identified by the phagocytes.

Opsonin

An active substance, such as $C3b$, used to coat a pathogen during phagocytosis to facilitate identification by phagocytes.

Chemotaxis

The movement of cells towards or away from a chemotaxin.

Lysis

The most important function of the complement system, involving the bursting of bacterial or mammalian cells by forming holes in their membranes.

Classical Pathway

One of the three pathways of complement activation, initiated by immune complexes (antigen-antibody complexes) and starting with the $C1$ complex.

Immune complexes

The initiator of the classical pathway, consisting of an antigen-antibody complex.

C1 complex

A complex made up of $C1q$, $C1r$, and $C1s$ ($C1qrs$); the $C1q$ portion resembles a golf club and attaches to antibodies.

C3 convertase (Classical Pathway)

The molecule $C4b2a$ which converts $C3$ into $C3a$ and $C3b$ during the classical pathway cascade.

C5 convertase (Classical Pathway)

The complex $C4b2a3b$ which activates $C5$ to cleave into $C5a$ and $C5b$.

Membrane Attack Complex (MAC)

The final structure formed in the complement cascade, ending with activated $C9$, which creates holes on the surface of the microbial membrane.

Alternative Pathway

A powerful complement activation pathway that can be directly triggered by fungi, viruses, bacteria, or tumor cells, starting with the activation of $C3$.

Factor B

A protein in the alternative pathway that is cleaved by Factor D into $Ba$ and $Bb$, where $Bb$ sticks to the membrane surface.

C3 convertase (Alternative Pathway)

The complex $C3bBb$ used in the alternative pathway to convert $C3$.

C5 convertase (Alternative Pathway)

The complex $C3bBb3b$ used in the alternative pathway to activate $C5$ for the common pathway.

Mannose-binding lectin (MBL) Pathway

The newest pathway which activates the complement system by the reaction of mannose-binding lectin to terminal mannose groups on some microorganisms.