Immune System Pillars: Lines of Defense, Phagocytosis, and Complement Flashcards

Vocabulary flashcards derived from lecture notes on the innate immune system, covering the lines of defense, cellular mechanisms like phagocytosis, the complement cascade, and the inflammatory response.

First Line of Defense

Physical and chemical barriers, such as the skin and mucous membranes, that prevent pathogens from entering the body.

Mucous Membranes

Epithelial layers lining the respiratory, digestive, and genitourinary tracts that secrete mucus to trap microbes, though they are more vulnerable than skin due to being thinner and moist.

Normal Microbiota

Resident microorganisms that protect the host by competing with pathogens for nutrients and space, often referred to as microbial antagonism.

Second Line of Defense

Innate immune responses, including phagocytosis, inflammation, and the complement system, that act once a pathogen has breached the first line.

Chemotaxis

The movement of phagocytic cells toward a chemical stimulus, such as microbial products or components of the complement system.

Phagocytosis

The process by which specialized cells like neutrophils and macrophages ingest and destroy foreign microbes or particles.

$MHC$ Class II

Molecules found on the surface of professional antigen-presenting cells, such as dendritic cells, used to present exogenous antigens to the immune system.

$MHC$ Class I

Molecules found on all nucleated cells that present endogenous antigens, allowing the immune system to monitor for intracellular infections like viruses.

$C3a$ and $C5a$

Fragments of the complement system that function as chemoattractants and triggers for inflammation.

$$C3b$$

A complement fragment that acts as an opsonin, coating microbial cells to make them more easily recognized and ingested by phagocytes.

$$C5b$$

The complement fragment that initiates the formation of the membrane attack complex to lyse foreign cells.

Alternative Pathway

The first complement pathway to act during an infection, triggered by the spontaneous breakdown of $C3$ and the binding of $C3b$ to the pathogen surface.

Lectin Pathway

The second complement pathway to act, triggered when mannose-binding lectin ($MBL$) attaches to specific carbohydrates on the surface of microbes.

Classical Pathway

The third complement pathway to act, which requires the presence of antibodies bound to antigens to initiate activation.

Toll-Like Receptors ($TLRs$)

Pattern recognition receptors that detect specific molecular signatures of pathogens; they can be located on the cell membrane or within intracellular compartments.

Interferons

Cytokines produced by virus-infected cells that signal neighboring cells to produce antiviral proteins, inhibiting the spread of the infection.

Natural Killer ($NK$) Cells

Innate immune cells that target and kill host cells that are infected with viruses or have become cancerous by inducing apoptosis.

Vasodilation

The widening of blood vessels during inflammation that increases blood flow to the site of infection, leading to redness and heat.

Margination

The process during inflammation where phagocytes stick to the endothelial lining of blood vessels near the site of injury.

Diapedesis

The movement of phagocytes through the walls of blood vessels and into the surrounding tissue to reach the site of infection.

Cytokines

Chemical signaling molecules released by cells to coordinate the immune response, including the recruitment of phagocytes during inflammation.

Histamines

Chemicals released during the initial stages of inflammation that promote vasodilation and increased vascular permeability.