Antibody Function and Complement Flashcards
What makes IgA Antibodies?
Plasma Cells in lymphoid tissues
What is the Secretory Component?
The receptor bound, exocytosed IgA. This is our first line of immunological defense in the gut against invading organisms.
Where else is IgA found?
Some monomer and dimer found in the plasma.
What is the importance of IgD?
It is a B cell receptor. We will learn about it more later.
IgE binds to what?
corresponding receptors on mast cells and basophils.
When IgE binds to _____ it induces the release of what?
basophils and mast cells. It triggers the release of histamine and in the case of mast cells only it triggers the release of eosinophil chemotactic factor. Eosinophils are important in killing parasites.
What are the three ways to activate the C cascade? All three pathways attempt to activate what?
- classical
- alternative
- Lectin
C3
The classical pathway deals with what antibodies?
IgM and IgG
Why is IgM a more efficient activator than IgG?
C1q must be bound by two Fcs simultaneously. It must either bind two IgGs at the same time that are close to each other or one IgM. Either one must be bound to an antigen to fit in the C1q.
what is the Classical C count in the pathway?
142356789
What inhibits Complement activity?
C1-inh (or C1 esterase inhibitor)
what is typical of the a and b components of a C molecule (e.g. C3a and C3b)?
b (Bound) usually stays bound to the membrane while a (away) usually floats away for further biologic activity.
how is the alternative pathway activated?
certain cell wall structures of microorganisms (e.g. a bacterium can activate Complement this way without an antibody. It is part of the innate immune system.
How does the alternative pathway work?
The cell wall provides a surface for the binding of properdin (P) which anchors C3b, factor B, and factor D. A trimer is formed: C3bDbC3b which can activate C5 and continue the cascade.
What activates the Lectin Pathway (specifically)?
A Lectin called Mannose Binding Protein (MBP or MBL).
What is a Lectin? and specifically MBP?
a protein that binds carbohydrates. MBP is a lectin which binds a kind of mannose found in carbs but not in humans.
What is the lectin pathway C count?
MBP42356789 (MBP is similar to C1q).
What associates with MBP when it binds mannose?
some serine proteases, called MASPS which activate C2 and C4 and get the cascade moving.
What is the Membrane Attack (lytic) Complex or MAC?
C5 (which can be activated by any of the three pathways in this case, but mostly by the classical pathway) activates 6789. 8 and 9 form a hole on the target cell membrane. It loses its ability to regulate osmotic pressure and pops.
Complement has four distinct functions. Name them and be able to describe a little about each.
- Lytic- MAC holes causing C lysis (Neisseria bacteria are the most susceptible to this defense)
- Opsonizing- C3b grabs onto membranes. If an antigen is opsonized by C3b phagocytes can get a firm grip on them. IgG is also Opsonizing– phagocytes have receptors for its Fc end called FcR. There are no FcR (phagocyte receptors) for IgM. The complement that IgM activates in opsonizing however.
- Chemotactic- C5a is chemotactic for phagocytes, especially neutrophils. Why there is inflammation in an antibody-mediated reaction.
- Anaphylatoxic- C3a,C4a, and C5a are all capable of releasing histamine (from mast cells and basophils). This causes increased blood flow and better chance for inflammatory cells to get out of blood and into tissues.
What is an immunogen?
An antigen that gives an immune response.
