Chapter 3Chapter 3

Immune SystemImmune System

Chapter 3Chapter 3

Immune SystemImmune System

Chapter 3 Immune System (Is)

Immune organs and immune tissues Central immune organs(primary lymphoid organs) Peripheral immune organ(secondary lymphoid organ

s) Immunocytes Lymphocytes(T,B cells and NK cells) APC(M ,DC,B cells)ɸ Other cells(neutrophil,basophil,eosinophil etc.) Immune molecules Antibody,Complement,Cytokine CD and adhesion molecules,MHC molecules

Human red blood cells (red), activated platelets (purple) and white blood cells - monocyte (green) and T lymphocyte (orange).

Colorized-SEM (scanning electron micrograph)

Magnification:-1200x--(Based on an image size of 1 inch in the narrow dimension)

Part I Central Immune organs

Central Immune Organs are the sites of generation, differentiation and maturation of immunocytes.

Bone marrow Thymus Bursa of Fabricius (the site of B cells maturation in birds)

The thymus is the site of T cell differentiation and maturation.

I. Thymus

1.The structure of Thymus

2. Cells in thymus and thymus microenviroment

(1)Thymus stroma cells (TSC) Thymus epithelial cells(TEC), Fibr

ocyte,Macrophages, Dendritic cells

(2)Thymocytes The cells migrate from the bone m

arrow to the thymus and then become thymocytes

(3)Thymus microenviroment TSC TEC: Secret thymus hormones and cytokines. Interaction between cells by direct contact. Extracellular matrix Active substance in local sites

3. Function of Thymus

(1) Development and differentiation of T lymphocytes in thymus

TSC interact with thymocytes directly by adhesion molecules.

TSC secrete various cytokines and thymus hormones.

Thymocytes secrete various cytokines.(2)Immune regulation of the thymus(3)Barrier function of the thymus

II. Bone marrow

The bone marrow is the site of generation of all circulating blood cells in the adult, including immature lymphocytes,and is the site of B cell maturation.

Functions of bone marrow

The site of generation of all immunocytes The site of differentiation and maturation of imm

unocytes The site of immune response of B cell,specifically

in secondary immune response.

III.Bursa(Bursa of Fabricius)

Specific immune organs in birdsThe site of differentiation and

proliferation of B cells in birds.

Part II Peripheral lymphoid organ

The site where lymphocytes locate,response to foreign antigens ,produce specific antibody and sensitized T lymphocytes.

Lymph node Spleen Mucosal associated lymphoid tissue (MALT) Skin associated lymphoid tissue (SALT)

I. Lymph node ( LN)

Lymph nodes are the organs in which adaptive immune responses to lymph-

borne antigens are initiated.

From http://medicine.ucsd.edu/clinicalmed/head.htm

A typical active lymphnode, e.g. in an infection

Surface Locations of Lymph Node Chains

Here’s a chance to revise your knowledge of:

Here’s a chance to revise your knowledge of:

1 mm

Functions of lymph nodes

Filter and eliminate foreign antigens.The site of immune response.The site of lymphocytes residence and

source of recirculation cells.

II. Spleen

The spleen is the major site of immune responses to blood-borne antigens.

Functions of spleen

The site of immunocytes residence. The site of immune response. Produce some active substances,such as co

mplement,et al. Function of filtration.

III. SALT

The skin contains a specialized cutaneous immune system consisting of lymphocytes and APCs (such as Langerhan’s cell)

Cellular components of the cutaneous immune system

IV. MALT

The mucosal surfaces of the gastrointestinal and respiratory tracts,like the skin,are colonized by lymphocytes and APCs that initiate immune responses to injested and inhaled antigens.

(1) Gut-associated lymphoid tissue (GALT) M cell: membranous epithelielial cell ---antigen transporting cell (2)NALT(N:nasal)(3)BALT(B:bronchial)

M cells establish immunity in the digestive tract

Composition of MALT

Functions of MALT and SALT

The first line of defense against foreign antigen.

The site of immune response.Participate in delayed hypresensitivity.

Part III Immunocytes

I. Hematopoietic stem cells and differentiation

II. Immunocytes

1. Lymphocytes2. Mononuclear phagocytes3. Other cells

III Homing and recirculation of lymphocytes

I. Homing of lymphocytes: the process by which particular subsets of lymphocytes selectively enter some tissues but not others is called lymphocyte homing.

(homing receptor on T lymphocyte and ligand on endothelial cell)

lymphocytes circulate among / between? blood and peripherial lymph organs

lymphocytes circulate among / between?

blood and peripherial lymph organs

Lymphocytes recirculation and homing

Naïve T lymphocytes home to lymph node as a result of L-selectin binding to its ligand on high endothelial venules,which are present only in lymph nodes.

Activated T lymphocytes,including effective cells,home to sites of infection in peripheral tissue,and this migration is mediated by E- and P-selectins and integrins.

2. Recirculation of lymphocytes

Lymphocyte recirculation is the process lymphocytes circulate repeatedly among blood,lymph,lymphoid organs and tissues.

Promote lymphocytes to contact with antigen throughout the body.

Promote effector cells migrate to inflammation sites rapidly.

Promote lymph tissue acquire supplement of new lymphocytes from circulatory pools.

Memory cells can participate in recirculation and secondary immune response.

3. Significance

Summary

Part IV Immune molecules

Membrane moleculesSecretory molecules