Immune System and Innate Immunity

1. Clean up damaged tissue
2. Manage beneficial microbes
3. Defend against pathogens
4. Destroy abnormal cells.

Commensals are usually harmless; pathogens cause disease; symbionts provide benefits.

Microbes living on skin and mucosal surfaces (bacteria, archaea, fungi, viruses) that help maintain metabolic and immune balance.

1. Adhesion
2. Cell invasion
3. Actin-Based motility

1. Respiratory (influenza)
2. Gastrointestinal (parvovirus)
3. Reproductive (trichomonas foetus)
4. Skin (staphylococcus psuedointermediates)
5. Vector-borne routes (insects; west Nile virus).

Epithelial barriers, specific immune cells, and soluble components such as complement.

1. Present before exposure
2. Germline-encoded
3. Rapid response
4. Broad specificity
5. No long-term memory.

1. Broad, conserved categories of microbial molecules.
2. Pattern-recognition receptors (PRRs).

Innate recognizes broad conserved motifs; adaptive recognizes highly diverse specific epitopes.

Barrier defenses attempt to contain the pathogen.

Local phagocytes and antimicrobial defenses respond.

Skin, respiratory tract, and gastrointestinal tract.

Tight junctions (mechanical), antimicrobial peptides (chemical), and microbes.

Skin is multilayered and non-resorptive; respiratory and GI epithelia are single-layered and resorptive.

Multiple cell layers, a lipid layer, and lamellar bodies containing lipids and antimicrobial proteins.

Mucus, cilia, surfactant, and a single epithelial cell layer.

Mucus, peristalsis, and a single epithelial cell layer.

Acidic environments inhibit or kill microbes.

Digests bacterial cell walls.

They disrupt microbial membranes by forming pores.

Macrophages and dendritic cells.

Specialized macrophages established in tissues during embryogenesis that can self-renew.

Circulating monocytes.

Behind the epithelial barrier.

In front of the epithelium within the alveolar lumen.

Kupffer cells.

Microglia.

1. Phagocytosis
2. microbe killing
3. apoptotic-cell clearance
4. cytokine production
5. antigen presentation.

1. Phagocytosis
2. microbial killing
3. rapid recruitment during inflammation.

1. Phagocytosis
2. cytokine production
3. antigen presentation
4. activation of innate and adaptive immunity.

Macrophages are normally present; neutrophils mainly enter tissues during inflammation.

Macrophages are long-lived; neutrophils are short-lived and die after phagocytosis.

Macrophages slowly form granulomas; neutrophils rapidly contribute to pus.

Cell-wall sugars/lipids, complement, and antibodies.

The phagosome fuses with lysosomes, creating a hostile phagolysosome.

O₂ → superoxide → H₂O₂ → hypochlorite (OCl⁻).

NADPH oxidase.

DNA and antimicrobial proteins released by neutrophils to trap extracellular microbes. SPIDER-MAN

Reactive oxygen species (ROS).

Microbial sensing causes macrophages and other cells to release cytokines and lipid mediators.

CXCL8 (IL-8).

CCL2

1. They sense danger
2. process antigen
3. migrate to lymph nodes
4. present antigen to T cells.

Phagocytosis and macropinocytosis.

Macrophages and dendritic cells.