Lecture Notes on the Immune System

Flashcards on Natural Killer Cells, Innate Immune System, Interferons and Complement System

Natural Killer Cells

Involved in targeting virally infected cells, directed against the absence of self.

Natural Killer Cell Pathway

Secretes perforin (which pokes holes in the membrane) and granzyme (which triggers the apoptotic cascade).

Innate Immune System

Considered nonspecific, produces toll-like receptors or nonproteins to recognize fractions of pathogens (pathogen-associated molecular patterns).

Pathogen-Associated Molecular Patterns (PAMPs)

Examples include lipopolysaccharide for bacteria and beta-glucan (found on all fungi). Receptors are used by macrophages, neutrophils, or normal body cells.

Innate Immune System's Role

Recognizes broad categories of pathogens, leads to expression of inflammatory responses.

Interferons

Proteins that interfere with viral replication; Type 1 (alpha and beta) act as a warning signal or alarm that a virus is present.

Complement System

A series of proteins functioning in a cascade, amplifying results with positive feedback; labels pathogens, sounds the alarm, and directly kills microbes.

Complement Proteins

Produced by the liver at a constant rate and found in interstitial fluids; can be activated in three different ways.

C3 Convertase

An enzyme required for activating complement, leading to inflammation (C3a) and sticking to invaders (C3b).

C5 Convertase

Recruits all other complement proteins to make the membrane attack complex, which pokes holes in the membrane.

Classical Pathway

Antibody sticks to the surface of the pathogen, and C1, 2, and 4 merge there to form a convertase.

Lectin Pathway

A protein (lectin) sticks to weird sugars on the surface of bacteria, and complement protein 1 sticks to that, cutting complement proteins 2 and 4 to make a convertase.

Alternative Pathway

C3 protein randomly breaks on its own and sticks to the microbe surface, and factors B, D, and P converge to form a convertase.

Opsonization

Sticking to cell surfaces so phagocytes can grab on and engulf the pathogen.

Inflammation

One of the effects of complement; small pieces of cut proteins serve as chemotactic and inflammation signals.

Direct Killing

One of the effects of complement; directly killing the pathogen via the membrane attack complex.

Enzymes on Cell Surfaces

Inactivate C3b to prevent complement from attacking our own cells.

Pyrogens

Triggered by parts of bacteria (lipoteichoic acid, LPS) or viral components, leading to the production of cytokines that trigger fever.

Adaptive System

Very specific methods for recognizing and labeling to enhance phagocytosis, alarm signals, and ways to kill invading pathogens or infected cells.