Download The Immune System

The Immune System
(Chapter 43)
Raj Patel
AP Biology
4/27/12
What Is It?

The Immune System is designed to help protect
the human body from outside threats

These threats include viruses, bacteria, and other
pathogens

There are two types of immunity defense: Innate
Immunity and Acquired Immunity.
Innate Immunity
Present at start of birth and provides broad
defense
 Has both external and internal defenses:

External Defenses
1) Skin = barrier that is hard to penetrate
 2) Mucous membranes = digestive and respiratory
tract linings that make mucus (traps microbes)
 3) Secretions = saliva, tears, etc. Has lysozymes that
digest bacterial cell walls.

(1)
(2)
(3)
Internal Defenses

1) Phagocytes =
attach to bacteria’s surface
polysaccharide receptors
 form lysosome vacuoles
 engulf bacteria
Types:
-Neutrophils enter bacteria site and then
engulf, but then self-destruct
-Macrophages reside in lymphatic tissue and
capture bacteria via netlike extensions
-Eosinophils discharge destructive enzymes
-Dendritic cells can also engulf bacteria
Internal Defenses
2) Antimicrobial proteins = impede microbe reproduction
through interferons
 3) Natural Killer cells = kill virus-infected/cancer cells by
releasing chemicals that cause apoptosis (programmed cell
death)
 4) Inflammatory response = histamine chemical increases
blood flow to bacteria site and helps clot

Acquired Immunity
Main proteins are cytokines, which help activate other
cells in the immune system (reaction pathway)
 Antigen = any molecule that elicits a response from
cytokines
 Epitope = portion of antigen that cytokines can bind
onto in order to recognize molecule

Acquired Immunity

2 Types of lymphocytes:
1) B lymphocytes (B cells) – receptors for antigens are Yshaped and have 4 polypeptide chains (2 heavy and 2
light).
2) T lymphocytes (T cells) – receptors for antigens have 2
polypeptide chains, α chain and β chain, attached by
disulfide bridge

MHC (major histocompatibility complex) attach to antigen and are
recognized by T cells.
 Class I MHC = found on all cells; bind peptides derived from
foreign antigens that are synthesized in the cell
 Class II MHC = bind peptides from foreign antigens that are
fragmented, or broken, from phagocytosis/endocytosis
Lymphocyte Development
Lymphocytes arise from stem cells in the bone
marrow
 B cells develop entirely in bone marrow
 T cells develop in thymus

Lymphocyte Diversity

Nearly impossible for two B cells to have same exact
receptors (same for T cells)

Each person has 1 million different B cells and 10
million different T cells

Differentiation is a result of random gene
rearrangements in mRNA sequences
Gene Rearrangements
Clonal Selection of Lymphocytes
When an antigen selects a B or T cell, the
stimulated lymphocyte divides into 2 clone
daughter cells
 1st clone is made of many effector cells that
combat the same antigen (short-lived)


2nd clone is made of memory cells that have
receptors for specific antigens (long-lived)
Clonal Selection of Lymphocytes

Clonal Selection – antigen driven cloning of
lymphocytes; consists of the steps:
 Primary Immune Response – peaks after 10-17 days
after initial exposure to antigen. Plasma cells (secrete
antibodies) are made.
 Secondary Immune Response – peaks after only 2-7
days after secondary exposure. This response is faster,
stronger, and longer.
Humoral/Cell-Mediated Immunity

Acquired
immunity is
separated into 2
main branches:
humoral immune
response and
cell-mediated
response.

Humoral defends
against pathogens
toxins.
Cell-mediated defends
against infected cells,
cancer cells, and tissues.

T Cells

Helper T Cells – when it recognizes an antigen, it
separates into clones and secrete cytokines that
stimulate nearby lymphocytes.

Cytotoxic T Cells – uses a surface protein CD8 that
keeps the binding between antigen and T cell
strong. Used against cancer/infected cells.
LINK
A Overview of the
Immune System
and Its Cells
B Cells

B Cells differentiate into a clone plasma cell and a
clone memory B cell once stimulated.

Once finished, the B cell sends the fragmented
remains of the antigen to a helper T cell to finish
off.
Antibody Classes

There are 5 main types of antibody classes:
Active and Passive Immunity

Active immunity – immunity response that is
triggered by exposure to an infectious molecule.
Immunization (Vaccination) - develops prior
to an active immunity response and depends on
a cell’s memory of the antigen.

Passive immunity – immunity response that is
triggered when antibodies from an immune
person is transferred to someone who is not.
Blood Groups and Transfusions
How Do They Work?




Type A blood cells have the A antigen on the surface
Type B blood cells have the B antigen on the surface
Type AB blood cells have both A and B antigens on the surface
Type O blood cells have neither on the surface
Acceptable Transfusions:
Immune Response Side-Effects

Sometimes, responses from the immune system can lead to diseases
and conditions that are a result of the response.
Allergies

Allergies are exaggerated (very sensitive) responses to specific antigens
called allergens that trigger the response.

In this case, plasma cells secrete antibodies usually on pollen grains (hence,
“spring allergies”). When the pollen grains enter the body again, they
induce the cell to release histamine and other inflammatory molecules
(called degranulation).

As part of the inflammatory response and increased blood vessel flow,
symptoms like sneezing, runny nose, watery eyes, and itchy nose can result.
Autoimmune Diseases

Autoimmune diseases – diseases that are triggered when
immune system loses tolerance against itself.

Antibodies targeted against the body’s own natural
molecules (histones, DNA breakdown) are released and
various diseases can result.

Ex.) Lupus – disease characterized by skin rashes,
fever, arthritis, and organ dysfunction.
Inborn (Primary) Immunodeficiencies

These deficiencies result from defects in the basic
development of immune system cells. Both innate and
acquired defenses can be seriously impaired.
Acquired (Secondary) Immunodeficiencies

These deficiencies can develop later in life and are caused by
some external agent as opposed to natural birth causes.

Serious developments can impair the immune system

Hodgkin’s Disease – damages the lymphatic system

AIDS (Acquired Immunodeficiency Syndrome) – this infamous
condition makes infected people severely susceptible to
immune system breakdowns even from the most basic coughs,
fevers, colds, etc.