Download Thymus

Chapter III
The tissues and organs of immune system
Immune system
immune organs or tissues
bone marrow
thymus
spleen
lymph nodes
Immune cells :
lymphocytes : T cells , B cells and NK cells
phagocytes: Dendritic cells ,macrophage ,PMN
immune molecules :
antibody
complement (补体）
cytokines
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 , DC
Medulla
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
thymus 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
B ells
T cells
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
Cortex :
Structure of Lymphoid
node( p38)
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
mucosa-associated lymphoid tissue, MALT)
is in the epithelia , lamina propria and
submucosal area of gastrointestinal,
respiratory and genitourinary 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
Lymphoid node-blood recirculation



Blood
Enter into paracortex of Lymphoid node
by high endothelial venules (HEV) in
efferent lymphatics
Thoracic duct
Tissue –lymphoid node-blood recirculation
Tissues
Afferent lymphatics
Lymphoid node
Blood
Spleen-Blood recirculation



Blood
Enter into white pulp of spleen via
central 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