Final - Awasthi’s study guide

Obj. 1

Antibody structure and types, parts of antibodies, and their unique characteristics.

🔹What is an ANTIBODY (Ab)?

A Y-shaped protein produced by Plasma cells that specifically BINDS an ANTIGEN.

What are the 4 chains that make up an Ab?

2 Light chains + 2 Heavy chains

What connects the heavy chains & light chains?

Disulfide bonds.

Which part of the Ab binds to Antigen?

Fab region.

What does Fab stand for?

Fragment Antigen Binding.

What is the function of the Fab region?

• Binds antigen/epitope

• Determines specificity

1. What is the Fc region?

2. What is it responsible for?

1. The Fragment crystallizable region of the Ab.

2. It is responsible for biologic effect/effector functions.

What are Fc region functions?

• Complement activation

• Opsonization

• ADCC

• Mast cell sensitization

What is the Variable region?

Located @ the tips of the Fab arms & determines:

• Antigen specificity

• Epitope recognition

What is the Constant region?

Determines:

• Ab class (IgG, IgM, etc.)

• Biologic function

What is a Paratope?

Ab binding site that recognizes the Antigen.

• Located: on the Ab

What is an Epitope?

Specific part of an antigen recognized by the antibody.

• Located: on the Antigen

What are the 5 Ab classes?

1. IgG

2. IgM

3. IgA

4. IgE

5. IgD

💭Think: DAMAGE => Ig - “DAMGE”

What is the most abundant Ab in the SERUM?

IgG

Which antibody crosses the placenta?

IgA

Which antibody is most important for toxin neutralization?

IgG

Main functions of IgG?

• Neutralization

• Opsonization

• Complement activation

• Secondary immune response

Which antibody is produced first in a primary immune response?

IgM

What is unique about IgM structure?

pentamer

Which antibody is best at activating complement?

IgM

Why does IgM have high avidity?

Because the pentamer has many antigen-binding sites.

What is the major mucosal antibody?

IgA

Where is IgA found?

• Saliva

• Tears

• Mucus

• Breast milk

Main function of IgA?

• Saliva

• Tears

• Mucus

• Breast milk

What does secretory IgA (sIgA) do?

Protects mucosal surfaces and helps prevent reinfection.

Which antibody mediates allergy?

IgE

Which cells does IgE bind?

• Mast cells

• Basophils

What else is IgE involved in besides allergy?

Parasitic infections.

Which monoclonal antibody targets IgE?

Omalizumab (Xolair)

Where is IgD mainly found?

On naïve B-cell surfaces

Main function of IgD?

Acts as a B-cell receptor.

What does ADCC stand for?

Antibody-Dependent Cellular Cytotoxicity

Which antibody region is involved in ADCC?

Fc regions binds Fc receptors on NK cells.

Which antibody region activates phagocytosis?

Fc region.

What is opsonization?

Coating a pathogen with antibody to improve phagocytosis.

What is the hinge region?

The flexible region connecting Fab and Fc portions.

• It allows movement/flexibility of the antibody arms.

⚙Mech of ADCC

1. Fab region of Ab binds Antigen on infected/tumor cell.

2. Fc portion of Ab binds to Fcγ receptor on the NK cell.

3. NK cell is activated and releases perforins and granzymes, inducing apoptosis of the cancer cell.

Obj. 2

Agglutination, precipitation, affinity, avidity, specificity, cross-reactivity.

🔹What is agglutination?

Agglutination is the clumping of particles or cells caused by antibodies binding multiple antigens together.

What kinds of things undergo agglutination?

• Bacteria

• RBCs

• Particles

• Cells

What kinds of things undergo agglutination?

• Bacteria

• RBCs

• Particles

• Cells

Why is IgM very good at agglutination?

Because IgM has very high valency and can bind many antigens simultaneously.

What is the purpose of agglutination?

• Immobilizes pathogens

• Enhances phagocytosis/removal

What is precipitation in immunology?

Precipitation occurs when antibodies bind soluble antigens and form insoluble immune complexes that precipitate out.

What is the difference between agglutination and precipitation?

Agglutination	Precipitation
Insoluble particles/cells	Soluble antigens
Visible clumping	Insoluble precipitate formation

What forms during precipitation?

Large antigen-antibody lattice network

What is affinity?

Affinity is the strength of binding between ONE epitope and ONE antibody binding site (paratope).

Affinity measures binding between what?

ONE epitope + ONE paratope.

High affinity means what?

Very strong antigen-antibody binding.

Which region determines affinity?

The variable region/Fab region

What is avidity?

Avidity is the overall binding strength of ALL interactions between antibody and antigen.

Difference between affinity and avidity?

Affinity	Avidity
ONE binding interaction	TOTAL combined binding strength
ONE epitope + ONE paratope	ALL bindings together

Which antibody has especially high AVIDITY?

IgM

👉Reason:

• Pentamer structure

• Many binding sites

Can low-affinity interactions still produce high avidity?

Yes — if many binding interactions occur simultaneously.

• Ex: IgM

What is specificity?

Specificity is the ability of an antibody to bind a PARTICULAR epitope/antigen.

What determines specificity?

The variable region (Fab region).

Why are monoclonal antibodies highly specific?

Because they bind a single epitope.

What is cross-reactivity?

Occurs when an Ab binds a different antigen that has a similar epitope.

Why does cross-reactivity happen?

Because different antigens may share structurally similar epitopes.

Is cross-reactivity always beneficial?

No.

👉It can provide Protection.

OR

👉Contribute to Autoimmune reactions/allergy.

What is molecular mimicry?

When pathogen epitopes resemble host epitopes, causing cross-reactive immune responses.

⭐️Sometimes a pathogen has an epitope that looks very similar to one of your own body’s proteins.

The immune system:

1. Makes antibodies/T cells against the pathogen

2. Those antibodies accidentally recognize your own tissues too

3. This causes a cross-reactive immune response

4. Can lead to autoimmune damage

This is called molecular mimicry.

Obj. 3

What is complement? What are three pathways, timeline of their stimulation, and functions of the complement components (opsonization, phagocytosis, inflammation). Anaphylactic shock reaction by which of the released complement factors?

🔹What is Complement?

Complement is a group of plasma proteins that work together to:

• destroy pathogens

• enhance inflammation

• promote phagocytosis

• assist antibodies and innate immunity

Is complement part of innate or adaptive immunity?

Mainly innate immunity, but it also interacts with antibodies/adaptive immunity.

What are the 3 complement pathways?

1. Classical pathway

2. Alternative pathway

3. Lectin pathway

What activates the classical pathway?

Antigen-antibody complexes.

Usually:

• IgG

• IgM

Which complement protein starts the classical pathway?

C1

Which immune system branch is the classical pathway associated with?

Adaptive immunity b/c Ab activate it.

What activates the alternative pathway?

Direct microbial surfaces/pathogens.

• No antibody required.

Which immune system branch is the alternative pathway associated with?

Innate immunity.

What is unique about the alternative pathway?

It can activate immediately W/OUT antibodies

What activates the lectin pathway?

Mannose-binding lectin (MBL) binding to microbial carbohydrates.

What does MBL recognize?

Mannose sugars on pathogen surfaces.

Is the lectin pathway innate or adaptive?

Innate immunity.

Which complement pathways activate FIRST to LAST during infection?

Alternative → Lectin → Classical

• Alternative & Lectin: b/c they do NOT require Ab.

• Classical: b/c it requires that Ab must FIRST be produced.

What is opsonization?

Coating pathogens to enhance phagocytosis.

Which complement component is the major opsonin?

C3b

What does C3b do?

C3b coats microbes and helps phagocytes bind and ingest them.

Which cells perform phagocytosis?

• Neutrophils

• Macrophages

How does complement enhance phagocytosis

C3b binds microbes and phagocyte complement receptors recognize C3b.

Which complement fragments are important inflammatory mediators?

The chemoattractants:

• C3a

• C5a

What are anaphylatoxins?

Complement fragments that trigger inflammation and mast-cell degranulation.

Which complement factors can cause anaphylactic shock reactions?

C3a and especially C5a.

• These are called anaphylatoxins.

Which complement factor is the MOST powerful anaphylatoxin?

C5a

What does C5a do?

• Mast-cell degranulation

• Histamine release

• Increased vascular permeability

• Neutrophil chemotaxis

• Strong inflammation

What does chemotaxis mean?

Movement/recruitment of immune cells toward infection.

What is the membrane attack complex (MAC)?

A pore-forming complement complex that lyses pathogens.

Which complement components form the MAC?

C5b-C9

What does the MAC do?

Creates pores in microbial membranes causing lysis.

🔥Complement Components table

Complement Component	Function
C3b	Opsonization
C3a	Inflammation/anaphylatoxin
C5a	Strong inflammation + chemotaxis
C5b-C9	Membrane attack complex

Obj. 3

Membrane attack complex formation steps and its function.

🔹What does MAC stand for?

Membrane Attack Complex

How does the MAC kill bacteria?

The MAC forms pores in the membrane causing:

• ion imbalance

• water influx

• osmotic lysis

What type of killing does MAC cause?

Cell lysis

Obj. 5

Phases and characteristics of immune response (innate immunity, adaptive immunity, and immunological memory).

🔹What are the two major phases/types of immunity?

1. Innate immunity

2. Adaptive immunity

What is innate immunity?

Innate immunity is the immediate, nonspecific first-line defense against pathogens.

Is innate immunity specific or nonspecific?

Nonspecific

How quickly does innate immunity respond?

Immediately or within minutes/hours.

Does innate immunity have memory?

No. No significant immunologic memory.

Main cells involved in innate immunity?

• Neutrophils

• Macrophages

• Dendritic cells

• NK cells

• Mast cells

Main components of innate immunity?

• Physical barriers

• Complement

• Phagocytes

• Cytokines

• Inflammation

• NK cells

Which complement pathways are part of innate immunity?

• Alternative pathway

• Lectin pathway

What are the characteristics of innate immunity?

• Rapid

• Nonspecific

• No memory

• Same response with repeated exposure