Immune system Supplementary slides Biol 384N

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) 2

Immune System Conventionally said to include 3

4 Thymus

Lymph system 5

6 Spleen

7 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