Complement Flashcards
What is complement?
a complex set of distinct serum proteins (more than 30) that interact in a very specific way to mediate and enhance host defense reactions
Where are most complement proteins synthesized?
liver
Where is C1 mainly produced?
intestinal epithelial cells
Where is factor D made?
adipose tissue
How many complement component participate in the classical pathway?
9
What two immunoglobulin classes are capable of activating complement?
IgG and IgM
How many immunoglobulin Fc fragments are needed for complement activation?
2 IgG fragments or 1 IgM fragment
What is the end result of the complement cascade (in conjunction with the antigen-antibody reaction)?
irreversible cell damage and lysis
How can serum complement be inactivated?
heating to 56*C or by allowing the serum to age
Why would complement need to be inactivated for certain serology testing?
can cause false + by lysing cells and/or utilizing their antigen in the procedure
What is anaphylatoxin?
mediator of inflammation that initiates the release of histamine from mast cells and increases vascular permeability, which allows the flow of serum antibody and complement to the affected area; result of the reaction of C3 and C5
What role does calcium play in complement activity?
required to hold together the C1 complex of C1qrs
What is magnesium’s role in complement activity?
required for C2 to become involved in the complement cascade
What is the order of complement components in the classical pathway?
C1, C4, C2, C3, C5, C6, C7, C8, C9
Which complement component is the most abundant?
C3
Which component is cytolytic?
C8
What does the presence of C9 do?
accelerates cell lysis
What is the alternate pathway for complement?
bypass mechanism that does not require interaction between C1, C4, and C2; natural mechanism for defense against microbial invasion (can be activated by exposure, before antibody is available)
What was the alternate pathway originally called, and why?
properdin pathway; was thought that properdin initiated it
What are the activators of the alternate pathway?
Gram-positive and -negative bacteria; fungi and yeast; certain viruses; certain parasites; and some tumor cells
How many plasma proteins comprise the alternate pathway?
6
Which plasma proteins participate in the alternate pathway that are not seen in the classical pathway?
factor B, factor D, properdin, factor I, and factor H
What specifically do factor I and factor H do in the alternate pathway?
prevent the process from proceeding uncontrolled
What is the third pathway of complement activation called?
lectin pathway
Does the lectin pathway require antibody?
no
What is the major constituent in the lectin pathway, and how does it work?
mannose- (or manner-) binding lectin (MBL); adheres to mannose, which is found mainly in the cells walls or outer coating of bacteria, viruses, yeast, and protozoa
Is MBL normally present in the serum?
yes, but it also increases during an initial inflammatory response
Can complement lyse bacteria?
yes, a few species (primarily Gram-negative)
What effect does complement have on opsonization?
cells with C3b on their surface tend to be more readily phagocytized; these cells tend to aggregate together which serves to promote the process
