Chapter III

The tissues and organs of immune system

Immune systemImmune system immune organs or tissuesimmune organs or tissues bone marrow bone marrow thymus thymus spleenspleen lymph nodeslymph nodes Immune cellsImmune cells : : lymphocytes : T cells , B cells and NK cellslymphocytes : T cells , B cells and NK cells phagocytes: Dendritic cells ,macrophage ,PMphagocytes: Dendritic cells ,macrophage ,PMN N immune moleculesimmune molecules : : antibodyantibody complement complement (( 补体）补体） cytokines cytokines adhesive molecules adhesive molecules

Immune organs Central immune organs or primary lymphoid organs The site that lymphocytes generate and mature into

functional cells Bone marrow or Bursa, and Thymus , Thymus , Peripheral immune organs or secondary

lymphoid organs and tissues The sites that T and B lymphocytes reside in and

respond to antigens spleen , lymph nodes , mucosal immune system

Immune organs

Section I Central immune tissues and organs

I. Bone marrow

1.The bone marrow is the site of generation of all circulating blood cells in the adult, including immature lymphocytes

2. The bone marrow is the site of B cell maturation

3. Bone marrow is the sites that secondary humoral immunity carries through

II. Thymus

1. The structure of thymus

Cortex outer cortex : immature T cells ( thymus cells) inter cortex : thymus epithelial cell, macrophage , DCMedulla Mature T cells + thymus epithelial cell, macrophage , DC

The structure of thymus

2. The function of thymus The thymus is the site of T cell maturation Secrete cytokine and thymulin-like molecules

Thymosin( 胸腺素） thymulin （胸腺刺激素） thymopoietin （胸腺生成素） To promote the proliferation , differentiation of t

hymus cells Barrier function ： blood-thymus barrier

Development of T cell in thymus

Section II Peripheral Immune tissues and organs

The immune organs /tissues or secondary

lymphoid organs/tissues are sites that T and B

lymphocytes reside in and respond to antigens

spleen

lymphoid nodes

mucosal immune system

(mucosal-associated lymphoid tissues, MALT)

I. Spleen

1. The Structure of spleen white pulp Central arteriole periarteriolar lymphoid sheaths (PALS) T–cell area : around the central arteriole contain T cells , dendritic and macrophage B -cell area: lymphoid follicles contain B cells and macrophage and dendritic cells primary lymphoid follicle secondary lymphoid follicle Red pulp: cellular cords : B cells , plasma cells and macrophage ,DC venous: blood

T cells

B ells

2. Function of spleen

The site of T and B cells residence B cells : thymus-independent area T cells : Thymus –dependent area

Site of immune response to antigens

Synthesize some bioactive substance component of complete

Filtering blood

II. Lymphoid nodes

Structure of Lymphoid node( p38)

Cortex :

Outer cortex: thymus-independent area : B cell-rich area

lymphoid follicle/lymphoid nodule :

primary lymphoid follicle : without germinal center

mature and naïve B cells

secondary lymphoid follicle : with germinal center

activated B cells and memory B cells and macrophage

Paracortex : T cell-rich area+ dendritic cells Medulla :

medulla cords: macrophage and plasma cells medulla sinus

2. Function of lymphoid node

The site of T and B cells residence B cells : thymus-independent area T cells : Thymus –dependent area

Site of immune response to antigens

Part of Recirculation of lymphocytes

Filtering blood

III. Mucosal immune system

Mucosal immune system, also named as muc

osa-associated lymphoid tissue, MALT) is in

the epithelia , lamina propria and submucosa

l area of gastrointestinal, respiratory and ge

nitourinary tract

（ I ） The constitution of MALT

Gut-associated lymphoid tissue, GALT

Nasal-associated lymphoid tissue, NALT

tonsils Bronchial-associated lymphoid

tissue, BALT : nodule

submucosa

（ II ） The function and features of MALT

Local immunity

Secrete sIgA

Section III Lymphocytes homing and recirculation

I. Lymphocyte homing

The process by which particular subsets of

lymphocytes selectively enter some tissues

but not others is called lymphocyte homing

II. lymphocyte recirculation

The continuous movement of lymphocytes between blood stream and peripheral lymphoid tissues is called lymphocyte recirculation

1. Pathway of lymphocyte recirculation

2. Significance of lymphocyte recirculation

Blood Enter into paracortex of Lymphoid node

by high endothelial venules (HEV) in

efferent lymphatics Thoracic duct

Lymphoid node-blood recirculation

Tissue –lymphoid node-blood

recirculation

Tissues Afferent lymphatics

Lymphoid node

Blood

Spleen-Blood recirculation

Blood Enter into white pulp of spleen via cen

tral artery

spleen venule

Significance of lymphocyte

recirculation

Renew the lymphocytes in peripheral lymphoid organs

Maximize the chances of specific encounter with antigen and initiation of adaptive immunity

Enable lymphocytes to lymphoid tissue throughout body and facilitate immune response to antigen

Review

1.Terms

MALT, Central immune organs, Peripheral immune organs, lymphocyte recirculation, Lymphocyte homing

2. Questions :

Significance of lymphocyte recirculation

The function of thymus, bone marrow, spleen , LN and

MALT