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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