CHAPTER 3: Adaptive Immunity (specific body defense system)

Immunity: refers to the ability of an organism to recognize and defend itself against infectious agents

Susceptibility: opposite of immunity, is the vulnerability of the host to harm by infectious agents

Immunology: the study of adaptive immunity and how the immune system responds to specific infectious agents and toxins

Immune system: consists of various cells, especially lymphocytes, and organs such as the thymus gland, that help provide the host with specific immunity to infectious agents

Innate immunity (genetic): exists because of genetically determined characteristics

All humans have immunity to many infectious agents that cause disease in pets and domestic animals

Adaptive immunity (acquired): immunity obtained in some manner other than heredity

Naturally acquired adaptive immunity is most often obtained by having a specific disease

Artificially acquired adaptive immunity is obtained by receiving an antigen by injection of vaccine or immune serum

Formed cellular elements of the blood

The Bursa of Fabricus

In chickens this is where B cells develop

B-lymphocyte- B cellHumoral immunity (antibodies)

T-Lymphocyte-T cellInvolved cell mediated

All distributed to the entire body by,Peyers path and nodule in digestive trace,Spleen, lymph nodes , blood and thymus

Lymphocytes give rise to two major types of immune responses

1. Humoral immunity: carried out by antibodies circulating in the blood

2. Cell mediated immunity: carried out by T cells and occurs at the cellular level

Specific immune responses are carried out by lymphocytes which develop from stem cells as do other white blood cells, red blood cells, and platelets

B lymphocytes (B cells): lymphocytes are processed and mature in tissue, referred to as bursal-equivalent tissue

T lymphocytes ( T cells): stem cells migrate to the thymus, where they undergo differentiation into thymus-derived cells

Definition-A network of conduits(vessels) carry a clear fluid called lymph.Travel only one way flow towards the heart.

The lymphatic system can be broadly divided into the conducting system and the lymphoid tissue.

The conducting system carries the lymph and consists of tubular vessels that include the lymph capillaries, the lymph vessels, and the right and left thoracic ducts.

The lymphoid tissue is primarily involved in immune responses and consists of lymphocytes and other white blood cells

Regions of the lymphoid tissue densely packed with lymphocytes are known as lymphoid follicles.

Lymphoid tissue- either structurally well organized as lymph nodes or loosely organized lymphoid follicles known as the mucosa-associated lymphoid tissue (MALT)

Lymp (contain plasma cell and excess fluid between spaces cell)

Flow in lymph capillaries->lymph vessel->passes through lymph nodes->return to venous blood

by lymphatic duct (right or left) Movement of lymph is by mechanical contraction of

skeleton muscle.

tonsil

Thymus gland

spleen

Lymph nodes

Lymphatic vessel

•it is responsible for the removal of interstitial fluid from tissues

•it absorbs and transports fatty acids and fats as chyle to the circulatory system

•it transports immune cells to and from the lymph nodes in to the bone

•The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.

•The lymph also carries lymphocytes from the efferent lymphatics exiting the lymph nodes

FUNCTION OF LYMPHATIC SYSTEM

Including , primary lymphoid organ-thymus and bone marrow Function- production and selection of lymphocytes Secondary lymphoid organ- lymph nodes, and the

lymphoid follicles in tonsils, Peyer's patches, spleen, adenoids, skin

Function - maintain mature naive lymphocytes and initiate an adaptive immune response

environment for the foreign or altered native molecules (antigens) to interact with the lymphocytes

Y-shaped protein molecules composed of four polypeptide chains – two identical light (L) chains and two identical heavy (H) chains

Constant regions: determines the particular class that an immunoglobulin belongs to

Variable regions: each chain have a particular shape and charge that enable the molecule to bind a particular antigen

Five classes of immunoglobulins have been identified in humans and other higher vertebrates

1. IgG: the main class of antibodies found in the blood accounts for as much as 20% of all plasma proteins

2. IgA: occurs in small amounts in blood and in larger amounts in body secretions (tears, milk, saliva and mucus)

3. IgM: found as a monomer on the surface of B cells and is secreted as a pentamer by plasma cells

4. IgE: has a special affinity for receptors on the plasma membranes of basophils in blood or mast cells in tissues

5. IgD: found mainly on B-cell membranes and is rarely secreted

The Structures of the Different Classes of Antibodies

IgA

IgM

IgE

IgG

IgD

In humoral immunity the primary response to an antigen occurs when the antigen is first recognized by host B cells

Primary response of B cells can occur by two mechanisms:1. B cells can be activated by binding antigen, proliferating

and forming plasma cells (T-independent antigens)2. Produces IgM antibody and no B memory cells are formed

(T-dependent antigens) Secondary response: when an antigen recognized by

memory cells enters the blood

Primary and Secondary Responses to an Antigen

Produces IgM antibody and no B memory cells are formed (T-dependent antigens)

Primary and Secondary Responses to an Antigen

Antibodies produced by humoral immune responses eliminate foreign agents in three ways:

1. Neutralization

2. Opsonization

3. Immune complexes

Summary of Humoral Immunity

Involves the direct actions of T cells

T cells interact directly with other cells that display foreign antigens

Involves the differentiation and actions of different types of t cells and production of chemical mediators (cytokines)

Cytokines: lymphokines and interleukins

Types of T cells: After T cells are challenged by antigens, the cells differentiate into one of several types of functioning T cells

Involves the response of T lymphocytes

T cells cannot be activated directly by antigens

Macrophages that have processed an antigen secrete the lymphokine interleukin-1 (IL-1), which activates T helper cells

T helper cells secrete interleukin-2 (IL-2) and activate delayed hypersensitivity cells and cytotoxic killer cells

IL-1 and IL-2 cause undifferentiated cells to become natural killer cells

The Reactions in Cell-Mediated Immunity

Summary of Cell-mediated Immunity: “CD” stands for cluster of differentiation