Chapter 20: Resistance and the Immune System
• Innate immunity is obtained by birth.
• Metchnikoff (1908) directly observed the activity of the immune
system in a clear-colored starfish.
o Doctrine of phagocytosis: a body responds to pathogens through
the release of macrophages at site of pathogen to initiate
o Macrophages take the material that they engulf, chop it up, and
display it on the surface.
▪ This material enters the lymph nodes and the lymph nodes
search for a b-cell or t-cell that match against that
material; that particular b/t cell is then activated.
Host Immune Defenses
• Immunology: study of how immune system functions to prevent
• Innate immunity: immediate response.
o Effector molecules (molecules present at birth); present in skin,
mucus, membranes, and secretions (tears, etc).
o Innate immunity keeps infection in check while cytokines are
sent in order to initiate adaptive immunity.
• Adaptive immunity: slow response.
o Takes about a week since it requires activation and antibody
o Highly specific to a particular pathogen.
o Antibodies are present for life.
Host Immune Defenses
• Blood consists of: o Fluid
▪ Serum: cell free part of blood.
▪ Water, minerals, salt, proteins, antibodies, hormones.
▪ Serum that contains clotting agents.
o Blood and immune cells
▪ RBC (erythrocytes)
▪ WBC (leukocytes)
• Neutrophils (phagocytes):
o Contain digestive enzymes and antimicrobial agents that can kill
• Eosinophils: contain toxic compounds to defend against parasites.
• Basophils: act in allergic reactions.
o Last only a couple weeks but mature into macrophages.
o Natural killer cells; destroys virus infected and abnormal cells.
▪ Kills cancer cells.
• Dendritic Cells
o Present in every portal of entry.
• Cells and Tissues Essential to Immune Function
• Thymus ensures that T/B-cell does not target the body (self-molecule).
o After being ‘educated’ by the thymus, these cells enter the
• Lymph nodes:
o This is where B/T -cells are located.
o Dendritic cells and macrophages display what they have
captured to the B/T-cells (recall—these are antigen presenting
2 ▪ Cortex: B-cells.
▪ Medulla: T-cells.
Invaders: Pathogen Identification
• Recognition Phase
o Body’s immune cells need to distinguish normal body cells from
o Identify self-molecule from non self-molecule.
▪ Pathogens have flagella, peptidoglycan,
lipopolysaccharides, etc… while the body’s cells do not.
• Activation Phase
o Neutrophils, macrophages, dendritic cells are put in action as
the first responders.
▪ Neutrophils come first; monocytes turn to macrophages;
dendritic cells come last.
• Effector Phase
o Notification: signaling molecules are sent by effector cells in
order to alert more cells (phagocytic) to the site of pathogenic
▪ Cytokine: a molecule secreted from cells (DC,
macrophages, T-cells) that communicates to other
phagocytic cells to the site.
• Interleukin: cytokines that are involved in the
communication between leukocytes; bind to
cytokine receptors on target cells.
• Chemokines: trigger attraction of leukocytes.
o Create a chemical gradient to attract cells to
• Has to acquire information from whatever has been infecting the
o This requires the presence of antigen presenting cells.
• We have billions of T-cells and millions of b-cells.
3 o However, it takes long to create antibodies since the T/B-cells
need to be educated.
Interleukins Between Leukocytes
• A macrophage has to trigger a specific response to a pathogen it has
Suppressor of Cytokine Signaling (SOCS)
• At some point, a cytokine storm is possible in which there are too
many white blood cells in an area; can be deadly.
• There is a gene pro