an integral part of the innate immune system

plays a major role in the inflammatory response directed against foreign antigens

cell lysis

initiation of the inflammatory response

classical pathway

alternate pathway

these two pathways result in activation of the terminal sequence

9 proteins triggered by antigen-antibody combination

proteins are called components and are viral neutralizers

components C1-C4 neutralize viruses

when a componenet is cleaved or fragmented by proteolysis it is denoted by a lower case letter

converts the next protein in the sequence into the active form

once enzyme activity is generated

IgM, IgG1, IgG2 and IgG3 are able to activate the classical pathway

IgM is the most efficient because it has multiple binding sites

one IgM molecule bound to the memebrane of the target cell is necessary to start activation

two IgG molecules in close proximity are nessary to activate complement

IgA, IgD and IgE DONT BIND COMPLEMENT

Classic Pathway Phases:

Recognition

Involves C1 (recognition unit)

comprised of 3 subunits C1q C1r and C1s

C1q: reacts directly with the Fc region of the antibod molecule

C1r and C1s: do not bind to the Ig; are involved in subsequent activation of the classical pathway

classical pathway phases:

recognition pathway sequence

1:c1q starts the classic pathway by attaching to the fc portion of two IgG antbodies or the Fc portion of one igM antibody

2: c1r and c1s complex with c1q to form a trimolecular complex of c1q, c1r, and c1s(recognition complex) that requires calcium for its integrity

3: once the recognition complex has formed c1r and c1s develop enzymatic activity:

c1r leaves c1s

c1s c