An immunoglobin that binds a specific antigen.

• Antigen(Ag): A substance that can be bound by an antibody.
• Immunogen: An antigen that induces an immune response.

• Product formed when Antigen(Ag)-Antibody(Ab) bind.
• H-Bonds and Hydrophobic interactions

• Tightness of binding
• Stability of the Ag-Ab complex
• with time, affinity increases

[Ag-Ab]/[Ag][Ab}

• First step in host's defense function
• High affinity Abs are better in vivo for host defense. (they can quickly bind)
• May lead to tissue destruction/disease. (Vasculitis, Glumerulonephritis

ELISA

Western Blot

• Exposure to infectious agent (HIV, anthrax)
• Evidence of Immunity
• Certain autoimmune diseases
• Allergic reactions to substances
• Immunodeficiency
• Malignant Lymphoid diseases (Too much antibodies)

• 4 polypeptide chains. 2 Light. 2 Heavy
• The L chains are either 2 κ(kappa) or 2 λ(lambda). NEVER one of each

• Di-Sulfide bonds that connect the 2 Heavy chains together.
• Allows movement of binding sites.

• It cleaves 2 seperate FAB fragments away from the Fc fragment.

• In generates 2 FAB (antigen binding sites) as one unit.
• Also slices up the Fc into a bunch of pieces.
• Important for research.

• Also called Complementary Determining regions.
• Sites of contact with antigen (Ag)

• IgA: (IgA1, IgA2)
• IgG: (IgG1, IgG2, IgG3, IgG4)

• The type of amino acids in the Constant domains of the H chain.

• Increase valency
• Increase binding capacity

• ≥50 V genes and about 5 J genes code for the Variable domains.
• A single C gene codes for the Constant domains.

• Alot of V,J, and D(for Diversity) genes encode for the Variable domain.
• Single C gene codes for H chain class and subclass.

IgM (sometimes IgD, depending on alternative splicing) 

It hangs out on the surface of B-cells waiting to intereact with an antigen.

2

The first one makes IgM(or IgD) which sits on the surface of the mature B-cell.

After contact with an antigen the Ig can change constant regions if needed. The B cell divides and activates into Plasma cells.

What is the difference between Secreted Ig(sIg) and Membrane Ig(mIg)

• The carboxyl(Fc) end of the Heavy chain
• Due to alternate splicing the mIg has a transmembrane portion that contains a small extra exon at the 3' end of the last constant domain.

• Going from Igm(or IgD) to IgG, IgA, IgE
• Involves  second gene rearrangement/recombination event.

• The part of the mRNA taken out during second gene rearrangement.

• Theory explains Ab specificity during immune response

• Each V,D, and J gene has many amino acid sequences.
• Any one of those sequences can be the last one transcribed and thus create even more diversity.

also called HLA (human leukocyte Antigens)

• Class I: All somatic. Controls CD8 T cells
• Class II: Controls CD4 cells
• Transplantation: control graft rejection.

• receptor for antigen binding by T cell.
• 2 types: αβ & γδ
• Gene rearrangement similiar to Ig
• Only binds Ag that is already attached to a MHC

What are antibodies' effector functions in host defense?

• Neutralization of infectious agents or toxins
• Immune phagocytosis
• Complement activation
• Antibody dependent cellular cytotoxicity (ADCC) using NK cells
• Enhancement of Ag presentation, T cell activation & Immune reactivity.