Immune system

Supplementary slidesBiol 384N

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Immune System

• More concept than a system• Separates “what’s me” from “what’s not me”• Every cell → some immune function• Some estimates, 25% total body weight• Some ways, most important system• (immediate death if immunity fails)

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Immune System

• Conventionally said to include

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Thymus

• Lymph system

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Spleen

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Bone Marrow

Innate Immunity

• Developmentally the earliest• Nonspecific defenses: fevers, vomiting,

diarrhea, urination.• Purging the body of pathogens.• Risky, especially for

infants• Granulocytes and monocytes: phagocytes,

neutrophils, macrophages.

Acquired Immunity

• Cell-mediated = activated T cells.• Thymus:• • processes these immature T cells,• •differentiates them,• • “teaches” them to recognize specific antigens,• •selects those T cells which can recognize the antigen.• •destroys T cells that self-react.• Antigen exposure → massive release of T cells (macrophages

release cytokines).• (cytokines = communicator peptides)• e.g., IL-1 cause T cells to proliferate to combat antigens.

Types of T cells

• •Cytotoxic (effector T cells) recognize and lyse abnormal cells such as those infected with bacteria, viruses, or fungi, or cancer cells or cells with the “wrong” HLA complex as in tissue transplantation.

• •Helper (CD4+) generate cytokines that stimulate other parts of the immune system.

Types of T cells

• Suppressor T cells help dampen immune reactions • (Prevent clonal selection of T cell clones that react against

self-antigens)•

• •Memory T cells are the way the immune system resembles which antibodies work against which type of invaders. Similar to consulting its library or database for what worked before.

• • •Natural killer can survey the body and attack antigens

without any pre-sensitization. Important in fighting precancerous cells or chronic viral infections.

Delayed Hypersensitivity Reactions (DHR)

• Component of cell-mediated immunity• DHR T cells attract other immune system cells

such as macrophages or neutrophils to the site of an infection, eventually generating a strong inflammatory reaction

• Examples: bee stings, nuts, poison oak• Repeat exposure strengthens the DHR • DHR mediates anaphylaxis

Immediate Hypersensitivity Reaction

• Allergies mediated by an antibody called IgE that directs mast cells to produce histamine → swelling, watery eyes, sneezing

Auto-immunity

• An immune response to one’s own tissues• RA was a recently discussed example• Thought to be due to weakened immune

system and general depletion rather than “immune overdrive”

• Difficult to treat via conventional medicine