Innate Immunity and Defense Mechanisms

This set of vocabulary flashcards covers the fundamental concepts of innate immunity, including anatomical and physiological barriers, antimicrobial proteins, pattern recognition receptors (PRRs), the inflammatory response, and phagocytosis.

Innate Immunity

The body's first line of defense against germs that responds non-specifically to all foreign substances and acts very quickly.

Cytokines

Chemical mediators produced to recruit immune cells to infection sites.

Complement Cascade

A process that identifies bacteria, activates cells, and promotes the clearance of antibody complexes or dead cells.

Epidermis

The thin outer layer of the skin containing tiers of tightly packed epithelial cells and waterproofing keratin.

Dermis

The thicker layer of skin composed of connective tissue containing blood vessels, follicles, and scattered myeloid leukocytes.

Keratin

A waterproofing protein found in the dead cells of the outer epidermis layer.

Mucins

Glycoproteins found in mucus that prevent pathogen adherence to epithelial cells.

Cilia

Hairlike protrusions of the cell membrane in the lower respiratory tract that propel mucus-entrapped microorganisms outward.

Gastric acidity

An innate physiologic barrier with a low pH (typically $3-5$ on skin, lower in stomach) that kills most ingested microorganisms.

Lysozyme

An antimicrobial protein in mucosal/glandular secretions that cleaves glycosidic bonds of peptidoglycans in bacterial cell walls.

Lactoferrin

A protein in secretions that sequesters iron to limit microbial growth and disrupts microbial membranes.

Psoriasin

An S100 protein found on the skin and in secretions that disrupts membranes to kill cells.

Calprotectin

An S100 protein that binds and sequesters divalent cations such as manganese and zinc to limit microbial growth.

Surfactant proteins SP-A and SP-D

Secretions of the respiratory tract that block bacterial surface components and promote phagocytosis.

Defensins ($\alpha$ and $\beta$)

Antimicrobial peptides that disrupt membranes of bacteria, fungi, protozoan parasites, and viruses.

Cathelicidin (LL-37)

An antimicrobial peptide in mucosal epithelia that disrupts bacterial membranes and has toxic intracellular effects.

Histatins

Lectins found in saliva that bind to fungal cell walls and enter the cytoplasm to cause harmful effects.

Dermcidin

An antibacterial and antifungal peptide produced by sweat glands that produces channels in membranes to disrupt gradients.

PRRs (Pattern Recognition Receptors)

Cellular receptors that detect pathogens by binding to pathogen-associated molecular patterns (PAMPs).

PAMPs (Pathogen-Associated Molecular Patterns)

Conserved molecular motifs derived from microbes that trigger cellular innate responses.

DAMPs (Damage-Associated Molecular Patterns)

Molecules released by cell and tissue damage that can be recognized by PRRs.

TLRs (Toll-Like Receptors)

Single-pass membrane-spanning PRRs characterized by leucine-rich repeats (LRRs) that recognize conserved microbial molecules.

CLRs (C-Type Lectin Receptors)

Cell surface PRRs that recognize carbohydrate components of fungi, viruses, and parasites.

NLRs (NOD-Like Receptors)

A large family of cytosolic proteins activated by intracellular PAMPs and substances alerting the cell to damage or danger.

Autophagy

A process initiated by NOD1 and NOD2 where membranes from the endoplasmic reticulum surround cytosolic bacteria to form an autophagosome for lysosomal destruction.

Rubor

Redness; one of the four cardinal signs of inflammation described by Celsus.

Tumor

Swelling (edema); one of the four cardinal signs of inflammation.

Calor

Heat; one of the four cardinal signs of inflammation.

Dolor

Pain; one of the four cardinal signs of inflammation.

Functio laesa

Loss of function; the fifth sign of inflammation added by the physician Galen.

Vasodilation

An increase in the diameter of blood vessels resulting in tissue redness (erythema) and increased temperature.

Exudate

Fluid with high protein content that accumulates in tissue during increased capillary permeability, contributing to edema.

Margination

The process where phagocytes adhere to the endothelial wall of blood vessels.

Extravasation

The emigration of phagocytes between capillary endothelial cells into the tissue.

Chemotaxis

The migration of phagocytes through tissue toward the site of invasion/inflammation.

Acute-phase proteins

Serum proteins, such as C-reactive protein, whose concentrations increase dramatically in response to tissue-damaging infections.

C-reactive protein

An acute-phase protein produced by the liver that binds to C-polysaccharide on bacterial and fungal cell walls to activate complement.

Histamine

A chemical released in response to tissue injury that causes vasodilation and increased capillary permeability.

Kinins

Small peptides in blood plasma, such as bradykinin, that cause vasodilation and stimulate pain receptors.

Fibrin

Insoluble strands that are the main component of a blood clot, used to wall off an injured area and prevent infection spread.

Phagocytosis

A type of endocytosis where a cell's plasma membrane expands to form phagosomes around particulate material like microorganisms.

Pseudopodia

Membrane evaginations to which bacteria attach during the initial stage of phagocytosis.

Fever

An abnormally high body temperature systemic response controlled by the hypothalamus.

Tachycardia

Rapid heart rate; a potential complication associated with increased metabolism during fever.

Acidosis

Increased acidity of the blood or tissue, which can be a complication of fever.