Immunology

Question 1

Epitope

Answer 1

Part of antigen that fits into receptor, aka antigenic determinant. Proteins can have several epitopes, binding to different antibodies or receptors.

Question 2

Allotype

Answer 2

Minor allelic differences in the sequence of immunoglobulins between individuals.

Question 3

Idiotype

Answer 3

Unique antibody combining region, made up of CDRs (complementarity-determining region) of both the light and heavy chains.

Question 4

What antibody can cross placenta from mother to fetus? What antibody is made by the fetus?

Answer 4

IgG - crosses placenta

IgM - made by fetus

Question 5

Classical Complement activation

Answer 5

IgG or IgM binds to antigen, allowing conformational change of Fc region of heavy chain. Two adjacent Fc regions bind to C1q –> C4 –> C2 –> C3 –> C5 (common meeting point between pathways)

Question 6

Alternative complement activation

Answer 6

activated by certain wall structures of bacterium (dextran, leans, zymosan, and endotoxin) in absence of antibody.

Question 7

Lectin Pathway

Answer 7

mediated by mannose-binding protein (MBP), which is a lectin. Lectins are proteins that bind foreign carbohydrates, found in bacteria and not humans.

Question 8

Role of complement (4)

Answer 8

1. Lytic – membrane attack complex (C5,6,7,8,9) causes holes in cell way
2. Opsonizing – C3b adheres to membrane and has receptors for phagocytic cells (PMN, macrophages) so they can grab hold and eat foreign material. (IgG also opsonizing, but not Igm bc has no FcR on IgM)
3. Chemotactic – C5a is chemotactic for phagocytes, especially neutrophils.
4. Anaphylactic – C3a, C4a, and C5a are all capable of non-specifically releasing histamine form mast cells or basophils –> increases blood flow.

Question 9

What cells show CD3, CD4, CD8, and CD20?

Answer 9

CD3 - all T cells (part of the T cell receptor)
CD4 - T helper
CD8 - CTL
CD20 - B cells 
"Cluster of differentiation"

Question 10

What the heck is MHC then, anyway?

Answer 10

“Major Histocompatibility Complex” - loads antigen
Class 1 - found on all nucleated cells - intrinsic pathway - peptides are synthesized within (CTL recognize peptides on class 1 - binds to CD8)
Class 2 - only on APC - extrinsic pathway - peptides are endocytosed (Th and Treg recognize peptides on class 2 - binds to CD4)
*** dendritic cells can present on both MHC 1 and 2, this activated both helper and killer T cells