Chapter 20: Resistance and the Immune System; Innate
The Immune System is a Network of Cells and Molecules to Defend Against
• Blood cells make up the body’s innate and adaptive immunities.
o Blood consists of fluid, clotting agents, and formed elements.
▪ Fluid: serum.
▪ Clotting agents: fibrinogen and prothrombin.
• Serum, in the presence of clotting agents, is referred
to as plasma.
▪ Formed elements: RBCs and WBCs.
o All blood and immune cells begin as pluripotent stem cells in
▪ Pluripotent stem cells can differentiate into myeloid and
lymphoid cell lines.
• Myeloid cells/progenitors can themselves
differentiate into two lines:
o Red blood cells and platelets
▪ Platelets: small disc-shaped cells that
function in blood clotting and assisting
o White blood cells.
• Lymphoid lines differentiate into B and T
lymphocytes, natural killer cells, and dendritic cells.
Leukocytes: White Blood Cells
• Lack pigment in cytoplasm; number about 4-12 thousand per
microliter of blood; different lifespans depending on cell type. • Can be identified by size, shape of cell nucleus, and staining of
• Granulocytes: leukocytes containing cytoplasmic granules and present
in skin, lungs, GI tract, skin breaks, portals of entry.
o Basophils: have cytoplasmic granules that stain blue with
▪ Function in assisting innate immunity.
▪ Work like mast cells; function in allergic reactions.
o Eosinophils: red or pink granules when eosin is applied.
▪ Contain cytotoxic proteins to defend against parasites.
▪ Also involved in allergy development and asthma.
o Neutrophils: multilobed cell nucleus (polymorphonuclear).
▪ Contain many granules that contain enzymes and other
▪ Most numerous leukocytes.
▪ Can use phagocytosis to engulf pathigens or foreign
▪ Last only 1-2 days.
▪ Also considered a phagocyte.
• Monocytes: single, bean shaped nucleus without granules.
o Monocytes mature into macrophages in infected tissues.
o Macrophages are very effective in phagocytosis and drive the
innate and acquired immunity in this way.
o Present in the spleen, lymph nodes, thymus, and throughout the
lungs, skin and nervous system.
o Phagocytes and agranulocytes.
• Lymphocytes: single large nucleus and no granules.
o Natural Killer cells: destroy virus infected cells and tumor cells.
o B-Lymphocytes/T-Lymphocytes: drive adaptive immunity.
• Dendritic Cells: resemble the dendrites of neurons.
o Located at skin and mucosal surfaces where they can respond
rapidly to bacterial or viral pathogens.
o Phagocytes; drive innate and adaptive immunity.
2 Lymphatic System is Composed of Cells and Tissues Essential to Immune
• Lymph: part of the interstitial fluid that supplies oxygen and nutrients
while collecting waste.
• Lymph is oved along through lymph vessels which collect at larger
lymphatic vessels; they are filtered by lymph nodes.
• Lymphatic tissues: sites where lymphocytes mature and divide.
o Primary lymphoid tissues: Thymus, bone marrow.
▪ Site of B and T cell maturation.
o Secondary tissues: sites where mature immune cells interact
with pathogens to carry out adaptive immune response.
▪ Spleen: contains immune cells and has them on standby to
monitor and fight infectious agents entering the body.
▪ Lymph nodes: neck, armpits, and groin.
• Contain macrophages and dendritic cells which
destroy pathogens in circulation.
Innate and Adaptive Immunity Compose a Fully Functional Human Immune
• Three step response to an invader in the body:
o Recognition: body’s immune self-determines which cells are
host-cells and which cells are not.
o Activation: appropriate immune cells are mobilized.
o Effector phase: effector/mobilized cells attempt to eliminate
• Immune system is composed of two parts:
o Innate immunity: first response to pathogen; nonspecific and
▪ These defense are general across different pathogens.
▪ Early Warning System
o Adaptive immunity: requires adaptation and is therefore slower
than the innate response.
3 ▪ Effector phase (antibodies and lymphocytes) can take
more than a week to generate response.
• Immune system requires chemical communication between immune
cells through the release of cytokines.
o Cytokines: signaling proteins.
▪ Interleukins: chemical mediators that moderate reactions
between leukocytes locally or systemically.
▪ Chemokines: trigger the attraction of leukocytes to sites of
▪ Cytokines are produced mostly by T-cells, DCs, and
Surface Barriers Are Part of Innate Immunity
• Host defensive barriers limit pathogen entry.
• Many portals of entry in the body that can be advantageous for
pathogens; intact skin, mucus membranes, body cavities.
• Skin: impenetrable barrier to infection.
o Outer layer is constantly ‘shedding’; skin is poor source of
nutrition; low water content makes it a desert.
• Mucus membranes (mucosa): epithelial lining of digestive, urogenital,
and respiratory tracts.
o Mucus (glycoproteins that trap heavy particles) line these areas.
• Low pH in vaginal tract.
o Due to the presence of Lactobacillus; break down glycogen into
acids, keeping pH down.
• Stomach acid (pH=2).
o However, polio, and hep A, typhoid/tubercle bacilli, and H. pylori
can cause ulcers.
• Bile: enters system at duodenum and serves as inhibitory substance.
4 • Defensins: cationic, antimicrobial ;eptides that damage membranes;
lyse pathogenic cells.
o Produced by neutrophils, NK cells, and epithelial cells of