Chapter 43 Campbell Immunology
Pathogens – disease-causing agents such as bacterium, fungus and virus
- gas exchange, nutrition, and reproduction require openings
- Immune cells produce receptor molecules that bind specifically to molecules from foreign cells or
viruses and activate defense responses (MOLECULAR RECOGNITION)
2 types of immune defense: Innate immunity (all animals) and adaptive immunity (vertebrates)
Innate immunity -Recognizing of traits shared by pathogens using small set of receptors with rapid
response
It has Barrier Defenses: skin, mucous membranes, secretions; Internal defenses: Phagocytic cells,
Natural killer cells, antimicrobial proteins, inflammatory response.
Adaptive immunity – recognizing specific traits to a pathogen using vast array of receptors with slower
response
2 Types of Adaptive immunity: Humoral response (antibodies defend against infection in body fluids)
and Cell-mediated response (Cytotoxic cells defend against infection in body cells)
Innate Immunity
Lysozyme, an enzyme that breaks down bacterial cell walls, further protects the insect digestive system
The major immune cells of insects are called hemocytes. Like amoebas, some hemocytes ingest and
break down microorganisms, a process known as phagocytosis
hemocytes release antimicrobial peptides: inactivate or kill fungi and bacteria by disrupting their plasma
membranes.
if a fungus infects an insect, binding of recognition proteins to fungal cell wall molecules activates a
transmembrane receptor called Toll
Host enzyme dicer-2 cuts the viral RNA into fragments, each 21 nucleotides long. Enzyme Argo then cuts
the viral mRNA, inactivating it and thus blocking synthesis of viral proteins.
Mammalian Innate Immunity: The mucous membranes that line the digestive, respiratory, urinary, and
reproductive tracts produce mucus, a viscous fluid that traps pathogens and other particles. Lysozymes,
Acid in our stomach, secretions from oil and sweat glands.
Cellular Innate defenses: Toll-like receptor (TLR), a mammalian recognition protein similar to the Toll
protein of insects
TLR3 – bind to double-stranded RNA of virus
TLR4 – immune cell plasma membranes, recognizes lipopolysaccharide (common in bacteria surface),
TLR5 – Recognize flagellin (bacterial flagella)
Two main phagocytic cells: Neutrophils and macrophages
Dendritic cells – mainly populate tissues, such as skin, that contact the environment.
Eosinophil – tissue of epithelium that tackles parasitic worms.
Natural Killer cells – kill cells with abnormal array of surface proteins. (Apoptosis)
Dendritic cells -> Lymph nodes -> stimulate adaptive immunity.
Antimicrobial peptide for mammals only: interferons and complement proteins
Interferons are proteins that provide innate defense by interfering with viral infections. Pharmaceutical
companies are making recombinant DNA technology to produce interferons.
lymphoid organs: the adenoids, tonsils, thymus, spleen, Peyer’s patches, and appendix.
Lymphatic vessels return lymph to the blood via two large ducts that drain into veins near the shoulders.
inflammatory response, a set of events triggered by signaling molecules released upon injury or
infection (Macrophages) -> Cytokines (signal molecules in recruiting neutrophils to the site of infection)
mast cells – release the signaling molecule called histamine (blood dilation and more permeable)
Pus - a fluid rich in white blood cells, dead pathogens, and debris from damaged tissue.
A systemic inflammatory response sometimes involves fever (released by macrophages)
Certain bacterial infections can induce an overwhelming systemic inflammatory response, leading to a
life-threatening condition known as septic shock.
Adaptive Immunity:
The adaptive response relies on T cells and B cells, which are types of white blood cells called
lymphocytes
Lymphocytes originated in bone-marrow then go to thymus (T-cells) or stayed (B-Cells). Third type
remain in the blood (Natural killer cells).
Lymphocytes -> elicit response to antigens via antigen receptors.
The small, accessible portion of an antigen that binds to an antigen receptor is called an epitope.
Each B or T cell thus displays specificity for a particular epitope.
B cell antigen receptor: Y-shaped with a pair of heavy chains and light chains linked with disulfide bridge.
- Constant region – vary little in amino acid sequences and bind to the plasma membrane.
B cells – 2 identical antigen-binding sites
Binding to antigen -> B-cell activation - > secrete protein called antibody (immunoglobulin or Ig). They
also have Y-shaped appearance. (SPECIFICITY NEEDED)
For a T cell, the antigen receptor consists of two different polypeptide chains, an a chain and a b chain
antigen receptors of T cells bind only to fragments of antigens that are displayed (major
histocompatibility complex molecule)
