Download The Immune System

The Immune System
KAUR NAVNEET
SCHNEIDER STARLA
Overview: Reconnaissance, Recognition, and
Response
 Immune system: a system that enables animals to
avoid/limit infections and ailments; defense system
made up of proteins, immune cells, etc.
 Pathogens: unwanted substances that cause disease
via infection
 Two types of immunity:


Innate Immunity
Acquired Immunity
43.1: In innate immunity, recognition and
response rely on shared traits of pathogens
 Innate immune responses included barrier
defenses as well as defenses to combat pathogens
that enter the body
1. Barrier defenses


Skin and the mucous membranes (anything on the surface, any
lining of the openings)
Gives an animal a physical barrier, and secretions also help
protect against infection (results in skin pH of 3-5)
2. Cellular innate defenses
 Fight pathogens that make it past the barrier (cuts, gashes,
burns)
 Includes white blood cells and antimicrobial proteins
There are problems with just relying on the
barrier system!
43.1 Continued: Innate Immunity in
Invertebrates
 Innate defenses include
 Exoskeletons
 Chitin-based barriers in insect
intestines
 Lysozymes: enzymes that digest
the cell walls of microbes
 Low pH in organs
 Hemocytes: immune cells in the
hemolymph (insect blood);
capable of phagocytosis
 Secretion of antimicrobial
peptides that disrupt pathogen
membranes
43.1 Continued: Phagocytic White Blood Cells
 Neutrophils are white blood cells that ingest and
destroy microbes in a process called phagocytosis
 Monocytes are another type of phagocytic
leukocyte. They migrate into tissues and develop into
macrophages, which are giant phagocytic cells
 Eosinophils are leukocytes that defend against
parasitic invaders (worms, jungle worms) by
positioning themselves near the parasite’s wall and
discharging hydrolytic enzymes
43.1: Antimicrobial Proteins
 Interferon proteins are
the proteins that help the
innate defense system to
fight the viral infections.

They cause cells adjacent to
infected cells to produce
substances to inhibit viral
replication.
 complement system
consists of 30 proteins; one
of the functions include the
lyse invading cells
43.1 Continued
 A local inflammatory response is triggered by damage to
tissue from a physical injury or the entry of pathogens
(cuts, burns)


It leads to release of numerous chemical signals
Histamines are releases by basophils and mast cells (these are 2
types of leukocytes) in response to an injury.


Histamines trigger the dilation and permeability of nearby capillaries.
This aids in delivering clotting agents and phagocytic cells to an
injured area.
Systematic inflammatory responses include fever and septic shock
 Natural killer (NK) cells help recognize and remove
diseased cells
Histamines!
43.2: In acquired immunity, lymphocyte
receptors provide pathogen-specific recognition
 Vertebrates have 2 types of lymphocytes: B cells & T cells

B lymphocytes (B cells) are responsible of producing antibodies
that fight infections


Most common in the blood and proliferates in the bone marrow
T lymphocytes (T cells) responsible in killing the foreign
substances that enter the body
 All blood cells come from stem cells in the bone marrow
 Antigens are foreign molecules that elicit a response by
lymphocytes. B and T cells recognize them by specific
receptors imbedded in their plasma membranes.
 Antibodies are soluble proteins secreted by B cells
during an immune response.
B and T Lymphocytes
43.2 Continued
 B- or T-cell activation occurs when an antigen
binds to a B or T cell. B-cell activation is enhanced by
cytokines.

In clonal selection, a lymphocyte creates two clone cells.
The result of clonal selection is a mass of cells specifically
designed to target that antigen. There are two types:
Effector cells: responsible for fighting the antigen
 Memory cells: these cells stay in the body, inactive long after the
antigen is gone, with receptors that will recognize the antigen if it
enters the body again; aids a body in generating a quick response
to infections

A memory cell doing it’s job…
MHCs
 Antigen-presenting cells: Upon recognizing a
pathogen (ingesting it, internalizing some pathogen
byproducts), MHCs bind to them so T cells can recognize
them; usually B cells
 Major histocompatability complex molecules
(MHCs): Molecules generated by genes (unique to every
individual), help display antigens and trigger T-cell
response; grafting foreign MHCs can aid in generating
new immune responses; can lead to rejected transplants


Class I: Found in all cells minus red blood cells
Class II: Found in macrophages, B cells, dendritic cells (more
common)
Why do we have so many different types of B
cells and T cells?
 Gene shuffling and genetic recombination!
 We have more than 1 million different types of B
cells!
 And, we have more than 10 million different types
of T cells!
Immune Responses:
 A single B or T cell only responds to ONE
antigen!
 Primary immune response: Upon first exposure
to an antigen; lymphocyte activated
 Secondary immune response: When the same
antigen appears in the body later; this response is
greater in response time and magnitude
43.3: Acquired immunity defends against
infection of body cells and fluids
 Two branches:


Humoral immune response: antibodies are produced to go
around the body; activation and clonal selection of effector B cells
happens in this response
Cell-mediated immune response: the body searches for and
destroys antigens; activation and clonal selection of cytotoxic T cells
happens in this response
 Helper T cells: Help both responses work; they secrete
cytokines after interacting with class II MHC molecules;
bound by a CD4 protein
 Cytokines: activate B cells and cytotoxic T cells
 Cytotoxic T cells: bind to class I MHCs; destroys
infected cells (either pathogen infection or cancer);
bound by CD8 proteins
43.3 Cont’d
 Activated B cells produce memory cells and
plasma cells
 Plasma cells: involved in secreting mass amounts
of antibodies, which go throughout the body
destroying antigens
 Antibodies work by:



Neutralization: They bind to the pathogen by the pathogen’s
proteins, this stops the pathogen from entering and damaging
cells
Opsonization: stimulates greater phagocytosis, eating the
antigens faster
Lysis: activates the complement system (a group of proteins
that fight infection)
Different Types of Immunity; Important things to
remember
 Active Immunity: Develops naturally or artificially
(via vaccination) in response to an infection
 Passive Immunity: antibodies are passed into the
individual (like infants receiving it via milk)
 Some antigens exist on red blood cells (which
helps determine type), so blood transfusions can be
rejected if the host body has non-self blood
antibodies to attack these foreign blood cells based
on their antigens

So, in order to make sure transplants go OK, doctors should
match the MHC molecules with the donor, because MHC
molecules are primarily responsible for rejecting
transplants
43.4 Disruptions in immune system function can
elicit or exacerbate disease
 How do localized allergies work?
 When an allergen first enters the body, IgE antibodies are
created. When the allergen leaves, these antibodies produce
molecules that bind to receptors on mast cells, so the next time
an allergen enters the body, it triggers these IgE molecules,
producing an allergic reaction! (Histamine production,
swelling, vascular changes, etc.)
 What are autoimmune diseases?
 The body turns against itself, producing antibodies to target
molecules in the body.
 Lupus, rheumatoid arthritis, multiple sclerosis, HIV/AIDS
(attacks helper T cells)
HIV attacking a helper T cell