(1) Innate Immune System Main Components

Innate immune system

the body’s first line of defense, present from birth and encoded in the germline

Speed of innate immune system

immediate, minutes to hours

Role of skin in innate immunity

tightly packed epithelial cells form a physical barrier

Role of GI tract in innate immunity

stomach acid and digestive enzmes destroy many microbes

Role of respiratory tract in innate immunity

mucus traps microbes and cilia move them out

Role of tears and saliva in innate immunity

contain enzymes that kill bacteria

Role of norma flora in innate immunity

beneficial bacteria outcompete pathogens for space and nutrients

Role of urine flow in innate immunity

flushes out potential invaders

Granulocytes

contain granules with defensive chemicals and act as first responders

Granulocyte types

• neutrophils

• eosinophils

• basophils

• mast cells

Neutrophils

phagocytose bacteria, destroy them with enzymes and reactive oxygen, first to infection site

Eosinophils

attack parasites and release toxic granules, seen in parasitic infections or allergies

Basophils

release histamine and other mediators in response to IgE, involved in allergic inflammation

Mast cells

release histamine, heparin, serotonin

What is the difference between mast cells and basophils?

mast cells live in tissues (skin, mucosa, lungs)

Monocytes

circulate in blood, can become macrophages once in tissues

Inflammatory monocytes

respond quickly to infection

Patrolling monocytes

help regulate inflammation

Macrophages

long-lived phagocytes and professional antigen presenting cells (APCs)

Kupffer cells

macrophages in liver

Osteoclasts

macrophages in bone

Microglial cells

macrophages in the CNS

Dendritic cells

professional phagocytes and APCs, the messengers between innate and adaptive systmes

Pathway of dendritic cells

capture antigens in tissues → migrate to lymph nodes → activate T and B cells

Natural killer cells

kill virus-infected and cancer cells by recognizing low or absent MHC class I on infected cells

What do natural killer cells release to trigger apoptosis?

perforin and granzymes

Complement system

a group of 30+ plasma proteins that enhance immune defense by opsonization, chemotaxis, and cell lysis

Opsonization

coating pathogens for easier phagocytosis

Chemotaxis

attracting immune cells to the infection

Cell lysis

forming a membrane attack complex (MAC) to burst pathogen cells

Complement activation pathways

• classical

• alternative

• end result

Classical activation pathway

antibody bound to antigen, activated by IgG and IgM

Alternative activation pathway

pathogen surface accumulates C3b, antibody independent

End result activation pathway

MAC punches holes in pathogen membranes, leading to cell lysis

Cytokines

signaling proteins that coordinate inflammation and recruit immune cells, help both innate and adaptive responses communicate

Pattern recognition receptors

specialized receptors on innate immune cells that detect common pathogen patterns

types of pattern recognition receptors

• toll-like receptors

• NOD-like receptors

• RIG-I-like helicases

Toll-like receptors

recognize bacterial cell walls, viral RNA

NOD-like receptors

detect bacterial components inside cells

RIG-I-like helicases

recognize viral RNA in the cytoplasm

Steps of phagocytosis

1. phagocyte follow chemoattractant signals to infection site

2. adheres to pathogen

3. engulfs into a phagosome

4. fuses with a lysosome

5. kills the pathogen

Bone marrow role in innate immunity

produces immune cells (CD4+, CD8+, CD34+)

Thymus role in innate immunity

T cell maturation and self-tolerance training

Spleen roles in innate immunity

filters blood; red pulp removes old RBCs, white pulp houses lymphocytes

Lymph node roles in innate immunity

filter lymph and present antigens to lymphocytes, key in immune activation

Characteristics of inflammation

• redness

• swelling

• heat

• pain

Steps of inflammation

1. blood vessels dilate

2. immune proteins, fluids, and cells rush to site

3. cytokines attract immune cells

4. innate and adaptive immunity participate