IBS week 1 innate immune system

50 Flashcards — Concepts in Immunology (up to slide 23)

What are the two main parts of the immune system

The innate immune system and the adaptive immune system.

What is the main difference between innate and adaptive immunity

Innate immunity is immediate and non-specific; adaptive immunity is slower but highly specific and creates memory.

Which cells belong to the innate immune system

Macrophages, neutrophils, dendritic cells, and natural killer (NK) cells.

Which cells belong to the adaptive immune system

T cells and B cells.

How quickly does the innate immune system respond

Within minutes after pathogen entry.

How quickly does the adaptive immune system respond

After several days, because specific B and T cells must expand.

Where does the adaptive immune response take place

In lymphoid organs such as lymph nodes, spleen, bone marrow, and thymus.

What are the four classical signs of inflammation

Heat (calor), pain (dolor), redness (rubor), and swelling (tumor).

What causes inflammation

Recognition of pathogens by innate immune cells through pattern recognition receptors (PRRs).

What happens when macrophages detect a pathogen in tissue

They phagocytose the pathogen, secrete cytokines and chemokines, and recruit neutrophils.

What does pus indicate at an infection site

The accumulation of dead neutrophils.

What are the main soluble components of the innate immune system

Complement proteins and pattern recognition receptors (PRRs).

What is the complement system

A group of plasma proteins that enhance immune responses through opsonization, recuitment of inflammatory cells, and cell lysis through MAC.

What are the three complement activation pathways

Alternative, Lectin, and Classical pathways.

What initiates the alternative pathway

Spontaneous activation of complement components on pathogen surfaces.

What inhibits the alternative pathway on host cells

Self-proteins that prevent complement activation on host surfaces.

What triggers the lectin pathway

Mannose-binding lectin (MBL) binds to carbohydrates on pathogens.

What triggers the classical pathway

Binding of IgM antibodies or C-reactive protein (CRP) to pathogens.

What do all complement pathways converge on

Activation of C3 protein.

What happens when C3 is activated

C3 is cleaved into C3a (inflammatory mediator) and C3b (opsonin).

What is opsonization

Coating of pathogens with C3b to enhance phagocytosis.

What does C3a do

Acts as an anaphylatoxin, increasing vascular permeability and recruiting immune cells.

What does the membrane attack complex (MAC) do

Forms pores in bacterial membranes, causing cell lysis.

Which innate immune cells can recognize pathogens directly

Macrophages, dendritic cells, and neutrophils via PRRs.

What do PRRs recognize

Pathogen-associated molecular patterns (PAMPs).

What are PAMPs

Conserved molecular structures found in pathogens, like lipopolysaccharides or viral RNA.

What is the function of PRRs

They help the immune system distinguish between self and non-self and activate immune responses.

Name four classes of PRRs. Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs).

What do C-type lectin receptors recognize

Carbohydrates on pathogen surfaces.

What do RIG-I-like receptors detect

Viral RNA in the cytosol, leading to type I interferon production.

What do NOD-like receptors detect

Bacterial molecules and viral RNA in the cytosol, leading to inflammatory cytokine production.

What do Toll-like receptors (TLRs) detect

TLRs detect PAMPs — conserved molecular structures present in pathogens but absent in the host, such as bacterial lipopolysaccharides (LPS), flagellin, and viral nucleic acids (DNA or RNA).

Where are TLRs located

On the cell surface and in endosomes (intracellularly).

What is the outcome of PRR activation

Production of cytokines, interferons, and activation of phagocytosis.

What is the main function of macrophages

Phagocytosis of pathogens and secretion of inflammatory cytokines.

Where are macrophages located

In tissues throughout the body.

What are cytokines

Signaling proteins that regulate immune cell activation, proliferation, and survival.

What are chemokines

Cytokines that control the movement (migration) of immune cells to infection sites.

What is the function of neutrophils

Short-lived phagocytes that kill bacteria and fungi using toxic granules.

What happens when neutrophils are defective

Patients become more susceptible to bacterial and fungal infections.

What is the function of dendritic cells (DCs)

They act as a bridge between the innate and adaptive immune systems by presenting antigens to T cells.

Where are dendritic cells found

In almost all tissues, especially near epithelial barriers.

What happens to dendritic cells after pathogen uptake

They migrate to lymph nodes via lymphatic vessels to activate T cells.

What is the function of natural killer (NK) cells

They kill virally infected or stressed cells early in infection.

How do NK cells recognize infected cells

By detecting missing MHC I molecules or stress-induced ligands.

What cytokine activates NK cells

Type I interferons (IFN-α and IFN-β).

What is the role of NK cells in viral infection

destroy virus-infected or stressed cells early in infection — before cytotoxic T cells (CD8⁺) are activated.

How does the innate immune response alert the adaptive immune system

Through dendritic cell activation and cytokine signaling.

What is the role of dendritic cells after migration

They present processed antigens to T cells in secondary lymphoid organs.

What is the main goal of the innate immune system

To eliminate pathogens quickly and activate the adaptive immune response.

What are the take-home messages from this section

Innate immunity provides the first line of defense, involves PRRs, complement, and phagocytic cells, and is essential for triggering adaptive immunity.