Chapter III General introduction 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 ,PMN phagocytes: Dendritic cells ,macrophage ,PMN immune moleculesimmune molecules : : antibodyantibody complement complement (( 补体）补体） cytokines cytokines adhesive moleculesadhesive molecules

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

ctional cells Bone marrow and Thymus Peripheral immune organs or secondary lymphoid or

gans and tissues The sites that T and B lymphocytes reside in and respo

nd to antigens spleen , lymph nodes , mucosal or cutaneous lymphoid tissues

Section I Central immune 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. 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

Immune regulation:

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 thym

ocytes

Section II

Peripheral Immune tissues and organs

The immune organs /tissues or secondary lymphoid orga

ns/tissues are sites that T and B lymphocytes reside in an

d respond to antigens

spleen

lymphoid nodes

mucosal immune system

(mucosal or cutaneous-associated lymphoid tissues, M

ALT,)

I. Spleen 1. The Structure of spleen white pulp Central arteriole peripheral 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

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 complement Filtering blood

II. Lymphoid nodes

Structure of Lymphoid node 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

post-capillary venules, PCV or high endothelial venules 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. Skin and mucosal immune system

Skin-associated lymphoid tissue Mucosal immune system, also named as mucos

a-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

Gut-associated lymphoid tissue, GALT (1) mucosa Epithelia: intraepithelial lymphocytes (IEL) : T cells

M cells lamina propria: lymphoid nodule aggregated lymphoid nodule or Peyer’s patches: B cells and T cells solitary lymphoid nodule: B cells and T cells (2) submucosa Scattered lymphoid tissues : T cells

intraepithelial lymphocytes (IEL) : T cells

In mice : 40-50% of lymphocytes come from thymus , T cells 50-60% of lymphocytes come from non-thymus ( from bone marrow) , T cells

M cells :

•Some of the epithelial cells overlying Peyer’s Patches are specialized membranous( M ) cells.

• M cells lack microvilli,are actively pinocytic, and transport macromolecules from the intestinal lumen into subepithelial tissues.

•They are thought to play an important role in delivering antigen to Peyer’s patches

submucosa

CD4+ large intestine IEL in micewith GVHD

CD4+ T CD4+ T CD4+ T0

10

20

30

normalcontrolGVHD

n=3po

sitiv

e pe

rcen

t

CD

4+

normal graft contral SGVHD

T receptor

CD

4/C

D8

CD

4/C

D8

T receptor

（ II ） The function and features of MALT

First defense line Site of immune response to antigens 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 hi

gh endothelial venules (HEV) in

efferent lymphatics Thoracic duct venule

Lymphoid node-blood recirculation

Spleen-Blood recirculation

Blood Enter into white pulp of spleen via cen

tral artery

spleen venule

Tissue –lymphoid node-blood

recirculation

Tissues Afferent lymphatics

Lymphoid node

efferent lymphatics

Blood

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