Immunology Study Guide on Antibodies, Cytokines, Complement, Serological Testing, & More

Immunology Study Guide – Exam 2 – Antibodies, Cytokines, Complement, Serological
Testing, Etc.

Ch 5 Antibody Structure & Function

Epitope: The specific part of an antigen that is recognized and bound by an antibody.

Paratope: The part of the antibody (on the Fab region) that binds to the epitope of an
antigen.

Primary and Anamnestic Immune Responses:

 Primary Response: First exposure to an antigen, slower response, mainly IgM
produced.

 Anamnestic (Secondary) Response: Faster and stronger response upon re-
exposure, predominantly IgG due to memory cells.

Fab (Fragment antigen-binding): The region of the antibody that binds to antigens;
includes variable regions of both heavy and light chains.

Fc (Fragment crystallizable): The tail region of the antibody that interacts with cell
surface receptors and complement proteins.

Hinge Region: Flexible region of the antibody that allows movement of the Fab arms for
better antigen binding.

J Chain: A protein that joins IgM and IgA monomers to form pentamers (IgM) or dimers
(IgA).

Affinity and Avidity:

 Affinity: Strength of binding between a single antigen-binding site and its epitope.

 Avidity: Combined strength of multiple interactions (e.g., IgM has high avidity due
to 10 binding sites).

Monoclonal Antibodies: Identical antibodies produced by clones of a single B cell;
specific to one epitope.

Polyclonal Antibodies: A mixture of antibodies produced by different B cells, targeting
multiple epitopes on an antigen.

Hybridoma: A laboratory-created cell formed by fusing a B cell (for antibody production)
with a myeloma (cancer) cell for indefinite growth.

Hemagglutination: Clumping of red blood cells caused by antibodies; used in blood
typing and virus detection.

Opsonization: Coating of a pathogen with antibodies or complement to enhance its
uptake by phagocytes.

Neutralization: Antibodies block the binding of pathogens or toxins to host cells.

, Serum Protein Electrophoresis: A lab technique that separates blood proteins by
charge/size to detect abnormal protein levels (e.g., multiple myeloma).



Antibody Structure

Antibodies (immunoglobulins) are Y-shaped glycoproteins made of:

 2 Heavy chains

 2 Light chains

 Fab regions (arms) for antigen binding

 Fc region (tail) for binding to immune cells or activating complement

 Disulfide bonds maintain the Y-shape

 Hinge region provides flexibility



Antibody Digestion with Pepsin and Papain

 Papain digestion: Produces two Fab fragments and one Fc fragment.

 Pepsin digestion: Produces a single F(ab')₂ fragment (both antigen-binding sites
remain connected), and destroys the Fc region.

Significance: Helped identify functional regions of antibodies.



Affinity vs Avidity

Term Definition Example

Affinit Strength of a single antigen-antibody High-affinity IgG binds tightly to one
y interaction epitope

Avidit Overall binding strength from IgM has low affinity but high avidity due
y multiple interactions to multiple arms

Heavy and Light Chains

 Heavy Chains: Determine antibody isotype (IgG, IgA, etc.); consist of one variable
and multiple constant regions.

 Light Chains: Either kappa (κ) or lambda (λ); contain one variable and one
constant region.

 Both combine to form the antigen-binding site.