Title: Animal Defense Systems
1Animal Defense Systems
- Animal defense systems are based on the
distinction between self and nonself. - There are two general types of defense
mechanisms - Nonspecific defenses, or innate defenses, are
inherited mechanisms that protect the body from
many different pathogens. - Specific defenses are adaptive mechanisms that
protect against specific targets.
2Animal Defense Systems
- White blood cells are important in defense.
- All blood cells originate from stem cells in the
bone marrow. - White blood cells (leukocytes) are clear and have
a nucleus and organelles. - White blood cells can leave the circulatory
system. - The number of white blood cells sometimes rises
in response to invading pathogens.
3Animal Defense Systems
- There are two main groups of white blood cells
phagocytes and lymphocytes. - Phagocytes engulf and digest foreign materials.
- Lymphocytes are most abundant. There are two
types B and T cells. - T cells migrate from the circulation to the
thymus, where they mature. - B cells circulate and also collect in lymph
vessels, and make antibodies.
4Animal Defense Systems
- Four groups of proteins play key roles in
defending against disease - Antibodies, secreted by B cells, bind
specifically to certain substances. - T cell receptors are cell surface receptors that
bind nonself substances on the surface of other
cells. - Major histocompatibility complex (MHC) proteins
are exposed outside cells of mammals. These
proteins help to distinguish self from nonself. - Cytokines are soluble signal proteins released by
T cells. They bind and alter the behavior of
their target cells.
5Nonspecific Defenses
- Vertebrate blood contains about 20 antimicrobial
complement proteins. - Complement proteins provide three types of
defenses - They attach to microbes, helping phagocytes
recognize and destroy them. - They activate the inflammation response and
attract phagocytes to the site of infection. - They kill invading cells.
6Nonspecific Defenses
- Phagocytes ingest pathogens. There are several
types of phagocytes - Neutrophils attack pathogens in infected tissue.
- Monocytes mature into macrophages. They live
longer and consume larger numbers of pathogens
than do neutrophils. Some roam and others are
stationary in lymph nodes and lymphoid tissue. - Eosinophils kill parasites, such as worms, that
have been coated with antibodies. - Dendritic cells have highly folded plasma
membranes that can capture invading pathogens.
7Nonspecific Defenses
- Natural killer cells are a class of nonphagocytic
white blood cells - They can initiate the lysis of virus-infected
cells and some tumor cells.
8Nonspecific Defenses
- The inflammation response is used in dealing with
infection or tissue damage. - Mast cells and white blood cells called basophils
release histamine, which triggers inflammation.
9Specific Defenses The Immune System
- Four characteristics of the immune system
- 1. Specificity Antigens are organisms or
molecules that are specifically recognized by T
cell receptors and antibodies. - The sites on antigens that the immune system
recognizes are the antigenic determinants (or
epitopes). - Each antigen typically has several different
antigenic determinants. - The host creates T cells and/or antibodies that
are specific to the antigenic determinants.
10Specific Defenses The Immune System
- 2. Diversity
- It is estimated that the human immune system can
distinguish and respond to 10 million different
antigenic determinants. - 3. Distinguishing self from nonself
- Each normal cell in the body bears a tremendous
number of antigenic determinants. It is crucial
that the immune system leave these alone. - 4. Immunological memory
- Once exposed to a pathogen, the immune system
remembers it and mounts future responses much
more rapidly.
11Specific Defenses The Immune System
- The immune system has two responses against
invaders The humoral immune response and the
cellular immune response. - The two responses operate in concert and share
mechanisms.
12Specific Defenses The Immune System
- The humoral immune response involves antibodies
that recognize antigenic determinants by shape
and composition. - The cellular immune response is able to detect
antigens that reside within cells. - It destroys virus-infected or mutated cells.
- Its main component consists of T cells.
- T cells have T cell receptors that can recognize
and bind specific antigenic determinants.
13Specific Defenses The Immune System
- When the body encounters an antigen for the first
time, a primary immune response is activated. - When the antigen appears again, a secondary
immune response occurs. This response is much
more rapid, because of immunological memory.
14Specific Defenses The Immune System
- Artificial immunity is acquired by the
introduction of antigenic determinants into the
body. - Vaccination is inoculation with whole pathogens
that have been modified so they cannot cause
disease. - Immunization is inoculation with antigenic
proteins, pathogen fragments, or other molecular
antigens. - Immunization and vaccination initiate a primary
immune response that generates memory cells
without making the person ill.
15B Cells The Humoral Immune Response
- Antibody molecules are proteins called
immunoglobulins. - Five Classes/Types of IG's.
- G,M,D,A and E
16Figure 18.10 Structure of Immunoglobulins (Part
1)
17Figure 18.11 IgG Antibodies Promote Phagocytosis
18T Cells The Cellular Immune Response
- T cells, like B cells, possess specific surface
receptors. - The genes that code for T cell receptors are
similar to those for immunoglobulins. - T cell receptors also have constant and variable
regions. - A major difference between antibodies and T cell
receptors is that T cell receptors bind only to
an antigenic determinant that is displayed on the
surface of an antigen-presenting cell.
19T Cells The Cellular Immune Response
- Activated T cells give rise to two types of
effector cells. - Cytotoxic cells, or TC, recognize virus-infected
cells and kill them by causing them to lyse. - Helper T cells, or TH cells, assist both the
cellular and humoral immune systems. - Activated helper T cells proliferate and
stimulate both B and TC cells to divide. - HIV
20Figure 18.16 The Interaction between T Cells and
Antigen-Presenting Cells (Part 3)
21Figure 18.15 Macrophages Are Antigen-Presenting
Cells
22Figure 18.17 (a) Phases of the Humoral and
Cellular Immune Responses (Part 1)
23Figure 18.17 (a) Phases of the Humoral and
Cellular Immune Responses (Part 2)
24Figure 18.17 (b) Phases of the Humoral and
Cellular Immune Responses (Part 1)
25Figure 18.17 (b) Phases of the Humoral and
Cellular Immune Responses (Part 2)
26T Cells The Cellular Immune Response
- T cells developing in the thymus are tested to
ensure that they will be functional and will not
attack normal self antigens. - If the developing T cell binds to one of the
bodys own normal antigens, it undergoes
apoptosis.
27T Cells The Cellular Immune Response
- For organ transplants to be successful, MHC
molecules must match otherwise, these same
molecules will act as antigens. - The cellular immune system is responsible for
rejection. - Rejection problems can be controlled somewhat by
treating patients with immunosuppressing drugs.
28Disorders of the Immune System
- The human immune system can overreact to a dose
of antigen and produce an inappropriate immune
response. Allergies are the most familiar
example. - Immediate hypersensitivity.
- Delayed hypersensitivity.