immune system entermedschool

Immunology in one line: what's the immune system trying to do?

Spot threats and remove them without wrecking your own tissues.

Pathogen means…

A disease-causing organism (virus, bacteria, fungi, parasite).

Antigen means…

A molecule the immune system can recognize as a target.

Antibody means…

A protein made by B cells that binds a specific antigen.

Antigen vs antibody (say it in 5 words so you stop mixing them):

Antigen = target. Antibody = binder.

Epitope is… (basic idea)

The specific part of an antigen that an antibody/receptor binds.

Innate vs adaptive immunity: what's the core difference?

Innate = fast, general. Adaptive = slower at first, specific, with memory.

Innate immunity is like…

Security guards: immediate response, same rules for everyone.

Adaptive immunity is like…

A detective + sniper: takes time to identify, then hits very specifically, and remembers.

Which immunity has memory (classic exam answer)?

Adaptive immunity.

Do innate and adaptive immunity work separately?

No, they work as a team.

What is inflammation trying to do (big idea)?

Bring immune cells and fluid to a problem area and isolate the threat.

The 4 classic signs of inflammation (high-school level):

Redness, heat, swelling, pain.

Fever is usually… helpful or harmful? (basic)

Usually helpful (within reason).

Immunity can be active or passive. What's active immunity?

You make your own antibodies and memory cells.

What's passive immunity?

You receive antibodies from someone else (no memory made).

Natural vs artificial immunity: what's natural active?

Getting infected and recovering (your immune system learns).

Natural passive vs artificial passive: give one of each.

Natural passive: antibodies from mother. Artificial passive: injected antibodies (immunoglobulin).

First line of defense (before any white blood cell shows up):

Physical and chemical barriers (skin, mucus, stomach acid, etc.).

Skin is a good barrier because… (pick the big reason)

It's a tough physical wall.

Mucus + cilia in airways: what's the point?

Trap particles/pathogens and move them out.

Stomach acid mainly defends by…

Killing microbes you swallow (low pH).

Innate immunity recognizes pathogens using… (big idea)

General patterns common to microbes (not specific to one strain).

Phagocytosis means…

Cells 'eat' and digest microbes/particles.

Neutrophils are best described as…

Fast first responders that phagocytose bacteria.

Macrophages are best described as…

Big phagocytes that also signal to other immune cells.

Dendritic cells are famous for what job?

Bridging innate to adaptive by presenting antigen to T cells.

Natural killer (NK) cells: innate or adaptive?

Innate.

NK cells mainly kill…

Virus-infected cells and some tumor cells.

Complement system (basic idea): what does it do?

Helps tag microbes, attract immune cells, and sometimes punch holes in pathogens.

Opsonization means…

Tagging a pathogen to make it easier for phagocytes to eat.

Interferons (basic idea): what do they signal?

Warn nearby cells about viral infection and ramp up defenses.

Innate immunity response time is usually…

Minutes to hours.

Adaptive immunity has two main arms. Name them.

Humoral (B cells/antibodies) and cell-mediated (T cells).

Humoral immunity is mainly about…

B cells making antibodies.

Cell-mediated immunity is mainly about…

T cells attacking infected cells and coordinating responses.

Adaptive immunity is 'specific'. Specific to what?

Specific to a particular antigen/epitope.

Clonal selection (basic idea):

Only the B/T cells that recognize the antigen get activated and multiply.

Why does the first exposure take time?

Because the right B/T cells are rare and need time to multiply and differentiate.

Memory cells are…

Long-lived B or T cells that respond faster next time.

B cells' main job (exam version)?

Make antibodies (via plasma cells) and create memory B cells.

Plasma cell is basically…

A B cell turned into an antibody-producing machine.

Do B cells make antibodies by themselves, or do plasma cells do it?

Plasma cells do most of the antibody secretion.

Antibodies mainly fight pathogens that are…

Outside cells (extracellular).

Antibodies help by doing what 3 big things?

Neutralize, opsonize, and activate complement (also agglutinate).

Neutralization means…

Antibody blocks the pathogen/toxin from binding to cells.

Agglutination means…

Antibodies clump pathogens together.

Antibody structure in one sentence (no chemistry):

Y-shaped protein with variable tips that bind antigen.

Variable region of an antibody does what?

Binds the antigen (specificity).

Constant region of an antibody is mainly for…

Interacting with immune cells and complement (the 'call backup' part).

Common trap: do antibodies kill pathogens directly?

Not usually. They block and tag so other systems clear the pathogen.

IgM vs IgG (high-yield, basic): which shows up first in a primary response?

IgM first.

Secondary immune response: which antibody is usually dominant?

IgG (faster and stronger).

T cells are mainly for…

Cell-mediated immunity: helping coordinate responses and killing infected cells.

Helper T cells (CD4) do what (in plain English)?

They coordinate the immune response (activate B cells and other immune cells).

Cytotoxic T cells (CD8) do what?

Kill infected cells (especially virus-infected cells).

Trap check: which T cell actually kills infected cells?

Cytotoxic T cells (CD8), not helper T cells.

Regulatory T cells (Treg) are mainly about…

Stopping the immune system from overreacting / attacking self.

Cytokines are basically…

Chemical messages between immune cells.

Common trap: do T cells make antibodies?

No.

T cells usually need antigen presented to them. Who presents it?

Antigen-presenting cells (like dendritic cells, macrophages, B cells).

MHC (major histocompatibility complex) is basically…

A display platform on cells that shows antigen pieces to T cells.

Very basic MHC rule: MHC I is on…

Most nucleated body cells.

Very basic MHC rule: MHC II is on…

Professional antigen-presenting cells (APCs).

If a virus infects a body cell, which immune cell is built to kill that infected cell?

Cytotoxic T cell (and NK cells early).

Vaccine goal in one line:

Train adaptive immunity so the second response is fast and strong.

Vaccine is active or passive immunity?

Active immunity.

Trap check: antibiotics vs vaccines - same thing?

No. Antibiotics treat bacteria; vaccines train immunity before exposure.

Another trap: vaccines 'cure' an infection you already have. True or false?

Usually false.

Live attenuated vaccine means…

Weakened pathogen that can still replicate a bit.

Inactivated (killed) vaccine means…

Pathogen is dead; can't replicate.

Subunit vaccine means…

Only part of the pathogen (antigen) is used.

Toxoid vaccine means…

Inactivated toxin from a pathogen (train immunity against the toxin).

mRNA vaccine (very basic idea):

Gives cells instructions to make an antigen so the immune system can learn it.

Booster shot is basically…

A reminder exposure to push a strong secondary immune response.

Herd immunity (basic):

If enough people are immune, the pathogen spreads less, protecting vulnerable people too.

Why do vaccines reduce severe disease even if infection can still happen?

Because memory responses control the pathogen faster before it causes major damage.

Passive immunization example (medical):

Giving pre-made antibodies (immunoglobulin) after exposure.

Maternal immunity: which type is it?

Passive immunity.

Primary immune response means…

Your first exposure to an antigen (slow start, smaller response).

Secondary immune response means…

Re-exposure to the same antigen (faster, stronger response).

Primary vs secondary: which one has a shorter lag time?

Secondary.

Primary vs secondary: which one produces MORE antibodies?

Secondary.

Primary response: what cell type is being created that matters for the future?

Memory B and T cells.

What does 'antibody titer' mean (basic)?

How much antibody is in the blood.

Graph trap: a higher antibody titer in secondary response means…

Faster neutralization and better protection.

Why do symptoms often feel milder on reinfection after vaccination?

Because the immune system controls the pathogen earlier (before it multiplies a lot).

If you mix up 'innate' and 'adaptive', use this: which one needs time to learn?

Adaptive.

If you mix up B and T: which one makes antibodies?

B cells (via plasma cells).

If you mix up helper vs cytotoxic T: which one coordinates?

Helper T (CD4).

If you mix up NK vs cytotoxic T: which one is innate?

NK cells are innate.

Common trap: vaccines are the same as getting sick. True or false?

False.

Common trap: 'antigens are produced by antibodies'. True or false?

False.

Allergy (basic): what's happening?

Immune system overreacts to a harmless antigen (like pollen).

Autoimmune disease (basic idea):

Immune system attacks self tissues.

Immunodeficiency means…

Weakened immune response (more infections).

Fast, non-specific immunity is called:

Innate immunity

Specific immunity with memory is called:

Adaptive immunity

Cell that turns into an antibody-secreting factory:

Plasma cell

Immune cells that make antibodies (in general):

B cells