BIOL 22000 Lecture Notes - Lecture 8: Immunoglobulin Therapy, Intracellular Parasite, Subclavian Vein
8 Jun 2018
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Chapter 8 The Immune System
8.1 Structure of the Immune System
INNATE AND ADAPTIVE IMMUNITY
• Innate immunity is composed of defenses that are always active against infection, but
lack the ability to target specific invaders over others
o Also called nonspecific immunity
• Adaptive or specific immunity refers to the defenses that target a specific pathogen
o Slower to act, but can but act faster to attack in subsequent infections
ANATOMY
• The bone marrow produces all of the leukocytes (white blood cells) that participate in
the immune system through the process of hematopoiesis
• The spleen is a location of blood storage and activation of B-cells, which turn into
plasma cells to produce antibodies as part of adaptive immunity
o When B-cells leave the bone marrow, they are considered mature but naïve
(because they have not yet been exposed to an antigen)
o These antibodies dissolve and act in the blood (rather than within cells) is called
humoral immunity (adaptive immunity)
• T-cells (adaptive immunity) mature in the thymus, a small gland just in front of the
pericardium, the sac that protects the heart
o T-cells are the agents of cell-mediated immunity because they coordinate the
immune system and directly kill virally infected cells
• Lymph nodes provide a place for immune cells to communicate and mount an attack
o B-cells can be activated here
• Other immune tissue can be found close to the digestive system, and is called gut-
associated lymphoid tissue (GALT) and include the
o Tonsils and adenoids in the head
o Peyer’s patches in the small intestine
o Lymphoid aggregates in the appendix
• KEY CONCEPT
o Organs of the immune system:
▪ Lymph nodes filter lymph (fluid that circulates lymphatic system) and are
a site where immune responses can be mounted.
▪ Bone marrow is the site of immune cell production.
▪ The thymus is the site of T-cell maturation.
▪ The spleen is a storage area for blood, filters blood and lymph, and is a
site where immune responses can be mounted.
• Leukocytes are divided into two groups of cells: granulocytes and agranulocytes
(absence of granules)
o Refers to the presence or absence of granules in the cytoplasm
o Both come from common precursor: hematopoietic stem cells
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o These granules contain toxic enzymes and chemicals that can be released by
exocytosis
▪ Particularly effective against bacterial, fungal, and parasitic pathogens
o Granulocytes include cells such as neutrophils, eosinophils, and basophils
▪ The names of these cells refer to the way that the cells appear after
staining with certain chemicals
o Agranulocytes include the
▪ Lymphocytes which are responsible for antibody production, immune
system modulation, and targeted killing of infected cells
▪ Monocytes are phagocytic (engulf another cell) cells in the bloodstream
o They become macrophages (formed in response to an infection or accumulating
damaged or dead cells) in tissues
▪ Microglia in the central nervous system
▪ Langerhans cells in the skin
▪ Osteoclasts in bone
• Innate immunity refers to the responses cells can carry out without learning
o Also known as the nonspecific immune response
• Adaptive immunity is developed as immune cells learn to recognize and respond to
particular antigens
o Also known as the specific immune response
o We can also divide the specific immune system into humoral immunity (driven
by B-cells and antibodies) and cell-mediated immunity (provided by T-cells)
8.2 The Innate Immune System
• The innate immune system consists of cells and structures that offer nonspecific
protection
NONCELLULAR NONSPECIFIC DEFENSES
• First line of defense is the skin (integument)
• Antibacterial enzymes called defensins can be found on the skin
• Some mucous membrane, including eye and oral, produce a nonspecific bacterial enzyme
called lysozyme, which is secreted in tears and saliva, respectively
The Gastrointestinal Tract
• The stomach secretes acid eliminating most pathogens
• Guts are colonized by bacteria that doesn’t cause infection
o Since there is already a large population, invaders are not able to compete
Complement
• The complement system consists of many proteins in the blood that act as a nonspecific
defense against bacteria
• Can be activated through a classical pathway (which requires the binding of an antibody
to a pathogen) or an alternative pathway (which does not require antibodies)
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• The complement proteins punch holes in the cell walls of bacteria, making them
osmotically unstable
• Complement is considered a nonspecific defense because it cannot be modified to target a
specific organism over others
Interferons
• Cells that have been infected with viruses produce interferons, proteins that prevent viral
replication and dispersion
• Interferons cause nearby cells to decrease production of both viral and cellular proteins
• Decrease the permeability of these cells, making it harder for a virus to infect them
• Interferons upregulate (the process of increasing the response to a stimulus) MHC class I
and class II molecules
o Increased antigen presentation and better detection of the infected cells by the
immune system
• Interferons are responsible for many “flu-like” symptoms that occur during viral infection
o Malaise, tiredness, muscle soreness, and fever
CELLS OF THE INNATE IMMUNE SYSTEM
Macrophages
• Macrophages, a type of agranulocyte, reside within the tissues
• These cells derive from blood-borne monocytes and can become a resident population
(permanent placed there)
• When a bacterial invader enters a tissue, the macrophages become activated
• The activated macrophage does three things
o First, it phagocytizes the invader through endocytosis
o Then, it digests the invader using enzymes
o Finally, it presents little pieces of the invader (mostly peptides) to other cells
using a protein called major histocompatibility complex (MHC)
▪ MHC binds to a pathogenic peptide (also called an antigen) and carries it
to the cell surface, to be recognized by cells of the adaptive immune
system
o In addition, macrophages release cytokines—chemical substances that stimulate
inflammation and recruit additional immune cells to the area
• MHC molecules come in two main classes: class I and class II
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