Antibodies Part I

antibodies

Soluble antigen receptors shed by B cells

antibodies

Found in many body fluids but is present in

high concentrations and easily obtained from

blood serum.

antibodies

Defend against different types of microbes by

binding to antigens and marking them for

elimination.

antibodies

Multiple classes exist to accommodate

different microbial types and environments

(blood, milk, body surfaces, etc.)

immunoglobulin

abbreviation: Ig

immunoglobulin

glycoprotein antibody molecules

immunoglobulin

most found in the γ globulins of serum

immunoglobulin

consists of 4 linked peptide chains

forming a bilaterally symmetrical Y-shape

molecule

immunoglobulin

They have 2 identical Fab regions linked

to a stem with an Fc region

heavy chains

Five main types of heavy chains (γ, μ, α, δ, ε)

corresponding to the five classes of

immunoglobulins: IgG, IgM, IgA, IgD, and IgE.

Five main types of heavy chains (γ, μ, α, δ, ε)

corresponding to the five classes of

immunoglobulins: IgG, IgM, IgA, IgD, and IgE.

heavy chain

Each heavy chain has a variable region (V_H)

and three or four constant regions (C_H1, C_H2,

C_H3, and sometimes C_H4).

Each heavy chain has a variable region (V_H)

and three or four constant regions (C_H1, C_H2,

C_H3, and sometimes C_H4).

There are two types of light chains, kappa (κ)

and lambda (λ).

Each light chain has a variable region (V_L) and

a constant region (C_L).

located at the amino-terminal ends of the

antibody. Highly diverse and form the antigen-

binding sites.

Complementarity-Determining Regions

(CDRs)- Within the variable regions, there are

three hypervariable loops called CDR1, CDR2,

and CDR3.

These loops form the antigen-binding site and

determine the specificity of the antibody.

The constant regions of the heavy and light

chains (C_H and C_L) determine the

antibody's class and effector functions.

interacts with cell surface receptors (Fc

receptors) and complement proteins, mediating

various immune functions like opsonization,

antibody-dependent cellular cytotoxicity

(ADCC), and complement activation.

Each immunoglobulin has two Fab regions.

Contain the entire light chain (both V_L and

C_L) and the V_H and C_H1 domains of the

heavy chain.

Responsible for binding to antigens.

Flexible segment between the Fab and Fc

regions in certain classes of immunoglobulins

(e.g., IgG, IgA, and IgD).

provides flexibility to the antibody molecule,

allowing it to adopt different conformations for

optimal binding to antigens.

most abundant immunoglobulin in the

bloodstream

produced by plasma cells in the spleen, lymph

nodes, and bone marrow

plays a major role in antibody-mediated immune

defenses

binds specifically to antigens, including those on

bacteria, causing clumping (agglutination) and

opsonization.

produced by plasma cells in secondary lymphoid

organs.

second most abundant immunoglobulin in

mammalian sera after IgG.

the major immunoglobulin produced during

primary immune responses.

rarely enter tissue fluids, even in acute

inflammation.

Very large size thus cannot enter tissue fluids.

predominates in a prumary immune response, whereas predominates in ler responses

produced by plasma cells situated beneath body

surfaces (ex. walls of the intestine, respiratory

tract, urinary system, skin, and mammary

glands).

Produced in large amount but mostly goes to the

intestine, bronchi, or milk leading to its serum

concentration in most mammals lower than IgM.

The secretory component is a peptide that binds

to IgA dimers to form secretory IgA (SIgA). This

protects the IgA from digestion by intestinal

proteases.

Sig A - the major immunoglobulin in the external

secretions of nonruminants.

IgA does not activate the complement pathway,

nor can it act as an opsonin but can, however

agglutinate particle antigens and neutralize

viruses prevents adherance of invading

microbes to body surface.

mainly made by plasma cells located beneath

the body surfaces

has a typical Y-shaped, four-chain

immunoglobulin with four constant domain in its

ε heavy-chain

is bound to tissue mast cells and occurs in

extremely low concentrations in serum.

triggers acute inflammation by acting as a

signal-transducing molecule

Has the shortest half-life of all immunoglobulins

(2-3 days)

found in several mammals, bony fish, and some

birds but is absent in certain species like rabbits,

cats, and chickens

found in several mammals, bony fish, and some

birds but is absent in certain species like rabbits,

cats, and chickens

primarily remains attached to B cells and very little

is released into the bloodstream

consists of two δ heavy chains and two light

chains

is evolutionarily labile and shows many structural

variations

In contrast, Horse, cow, sheep, dog, monkey,

and human IgD has three heavy chain constant

domains.

Mouse IgD lacks a Cδ2 domain, thus, has only

two constant domains in its heavy chains.

Pig IgD has a short hinge coded for by a single

exon.

Allotypes- Genetic variations in

the constant region of

immunoglobulins between

individuals of the same species.

Idiotypes- Unique variable

regions (antigen-binding sites) of

each antibody.

-specificity for antigen

Idiotypes- Unique variable

regions (antigen-binding sites) of

each antibody.

-specificity for antigen