Specific Immune Defenses lecture final pt.2

🧠 1. WHAT ARE ANTIBODIES?

👉 Antibodies = proteins made by B cells to fight pathogens

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🔬 Structure (what they look like)

• Y-shaped molecule

• Made of 4 protein chains

• At the tips of the Y = antigen-binding sites

👉 Each tip binds a specific antigen

💡 Catchy phrase:
“Y shape = grab the germ.”

🎯 Important idea:

• Each antibody fits ONE specific antigen

💡 Phrase:
“Lock and key.”

🧬 2. ANTIBODY FAMILIES (IMMUNOGLOBULINS)

👉 Called Immunoglobulins (Ig)

There are 5 types :

• IgA

• IgD

• IgE

• IgG

• IgM

💡 Memory trick:
“ADEGM” (say: 'a-de-gum')

MEGA D

⭐ 3. IgG (MOST IMPORTANT ONE)

👉 This is the main antibody in your body

🧠 Key facts:

• Most common

• Longest lasting

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💥Functions of IgG (KNOW THESE) 1. Activates complement

• Starts immune attack chain

💡 Phrase:
“IgG starts backup attack.”

2. Neutralizes toxins

• Blocks harmful substances

💡 Phrase:
“IgG blocks toxins.”

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3. Blocks pathogen receptors

• Prevents germs from attaching to cells

💡 Phrase:
“Stops germs from sticking.”

👶 VERY IMPORTANT:

igG

👉 IgG is the ONLY antibody that crosses the placenta

• Gives baby immunity before birth

💡 Phrase:
“IgG = goes to baby.”

4. Forms opsonins

• Tags pathogens so immune cells can eat them

💡 Phrase:
“Tags it so it gets eaten.”

🟢 4. IgA (PROTECTS BODY SURFACES)

👉 Found in body secretions

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🔬 Structure:

• Dimer (2 antibodies joined together)

💡 Phrase:
“IgA = double antibody.”

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🌊 Where IgA is found:

• Saliva

• Tears

• Mucus

• Breast milk ( colostrum )

💡 Phrase:
“IgA lives in liquids.”

igA more facts

🍼 Colostrum (VERY IMPORTANT)

• First breast milk

• High in IgA

👉 Coats baby's GI tract

💡 Phrase:
“First milk = first protection.”

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🛡 Function of IgA:

• Coats surfaces of:

  • GI tract

  • Respiratory tract

  • Genitourinary tract

👉 Prevents pathogens from entering

💡 Phrase:
“IgA = bodyguard at entrances.”

IgG vs

igA

Antibody	Key Feature	Main Job
IgG	Most common	Long-term protection + crosses placenta
IgA	Dimer, secretions	Protects body surfaces

• IgG = most important (long-lasting, crosses placenta)neutralizes toxins, blocks receptors, forms opsonins, and crosses the placenta

• IgA = protects surfaces (mucus, milk, saliva)

is a dimer found in secretions like saliva, tears, mucus, and colostrum, where it protects body surfaces."

🟥 1. IgM (FIRST RESPONDER)

🔬 Structure:

• Pentamer = 5 Y-shaped antibodies stuck together

💡 Phrase:
“IgM = Mega (5 units).”

🎯 What IgM does: 1. Clumps antigens together (agglutination)

• Grabs multiple pathogens at once

• Sticks them together → easier to destroy

💡 Phrase:
“IgM = clumps enemies.”

igM FACTS

2. Used in agglutination tests

• Labs use IgM to detect infections

💡 Phrase:
“IgM = lab clumping test.”

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3. First antibody made during infection

👉 Shows up EARLY

💡 Phrase:
“IgM = first on the scene.”

🟪 2. IgE (ALLERGIES & PARASITES)

🎯 What IgE responds to:

• Parasitic worms

• Allergens (like pollen, food, etc.)

💡 Phrase:
“IgE = worms + allergies.”

🔗How IgE works (step-by-step):

1. IgE binds to the parasite (worm)

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2. Immune cells attach to IgE

👉 Especially:

• Eosinophils

• Also activates:

  • macrophages

  • natural killer (NK) cells

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3. These cells get activated

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4. They release chemicals:

• Perforin enzymes

• Other toxic substances

👉 These damage/kill the parasite

💡 Phrase:
“IgE = tag → recruit → destroy.”

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⚠ Important idea:

• Same process happens in allergies (but overreacts)

🟨 3. IgD (B CELL RECEPTOR)

🎯 Main function:

• Found on immature B cells

• Acts as a receiver

👉 Helps B cells recognize antigens

💡 Phrase:
“IgD = B cell detector.”

🧠 Key idea:

• Not really circulating in blood much

• Mostly stays on B cell surface

🔥 PUTTING ALL 3 TOGETHER

IgM, IgE,

IgD

Antibody	Structure	Main Job
IgM	Pentamer (5 units)	First response, clumps antigens
IgE	Single	Parasites + allergies, activates eosinophils
IgD	Receptor	Found on immature B cells

• IgM = first + clumping

• IgE = fights parasites +causes allergies

• IgD = B cell receptor

acts as a receptor on immature B cells.”

🧬 Antibody-Mediated (Humoral) Immune Response

This is the part of the immune system where B cells make antibodies to fight infections.

It happens in 3 stages :

1. Recognition of invader

2. Activation of B lymphocytes

3. Antibody response

1⃣ Recognition of Invader (Step 1)

This is the slowest and hardest step , especially during the first infection .

What happens:

• Your body must identify antigens (markers) on the invading microorganism.

• B cells are already present at birth for all possible antigens .

• There are:

  • 500+ genes

  • Creating about 10 trillion possible B cell variations

• These genes are randomly recombined to make different B cell receptors.

1⃣ Recognition of Invader (Step 1)

B cell receptors:

• Each B cell has a receptor called IgD

• This receptor sits on the surface of the B cell

• Each receptor is shaped to match a specific antigen

Key idea:

• Only a tiny number of B cells will match any one antigen.

• So the correct B cell must be found and activated .

1⃣ Recognition of Invader (Step 1)

Why the first infection is slow:

• Because the body must search through millions of B cells

• Very few match the invader

• So recognition takes the most time during first exposure

2⃣ Activation of B Lymphocytes (Step 2)

Once the correct B cell is found:

• That B cell is activated

• It starts copying itself (cloning)

• This creates many identical B cells

These cloned cells become:

• Plasma cells → make antibodies

• Memory B cells → remember the invader for next time

3⃣ Antibody Response (Step 3)

Now the body fights the infection:

• Plasma cells releasing antibodies

• Antibodies bind to antigens on the invader

• This helps:

  • Neutralize the pathogen

  • Mark it for destruction by other immune cells

⭐ Big Picture Summary

• Antibody mediated (humoral) response

• Your body already has millions of different B cells ready at birth

• Each B cell has a unique receptor (IgD)

• During infection:

  • The correct B cell must be found first (slow step)

  • Then it is activated and cloned

  • Then it produces antibodies to fight the infection

🧬 2⃣ Activation of B Cells (Simple Version)

Once the right B cell is found (the one that matches the antigen), the immune system “turns it on.”

activation steps of B cells

⚡ Step 1: B cell gets activated

• A specific B cell that matches the antigen is activated

• “Specific” means it only responds to that exact invader

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🔁 Step 2: The B cell multiples (clones itself)

• The activated B cell divides repeatedly

• This makes many copies of itself

These copies become TWO types of cells:

🧪 1. Plasma B Cells (most of them)

What they do:

• They are the active fighter cells

• They produce antibodies

Key facts:

• Each plasma cell releases thousands of antibodies per minute

• Antibodies attach to antigens on the invader

• When antibodies stick to the invader, they form an:

  • antibody-antigen complex

What that does:

• This “tags” the microorganism

• It signals other immune cells: “destroy this!”

Lifespan:

• Plasma cells only last about 5–7 days

• They fight fast, then die off

🧠 2. Memory B Cells (long-term protection)

What they are:

• They are inactive B cells

• But they are “trained” for a specific antigen

Key idea:

• They are partially activated during the first infection

• But they do NOT produce antibodies right away

What they do:

• They stay in the body long-term

• They “remember” the antigen

Why they matter:

• If the same invader shows up again:

  • They activate very quickly

  • They make antibodies much faster than the first time

🧠 BIG SIMPLE SUMMARY

When a B cell is activated:

1. 🔍 A matching B cell is found

2. 🔁 It copies itself

3. It becomes:

   • 🧪 Plasma cells → make tons of antibodies (short-term attack)

   • 🧠 Memory cells → stay for future protection

• Plasma cells = fight NOW

• Memory cells = remember for LATER