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Immune System
Immune System
1 Constituents: Lymphocytes in blood vessels,
lymphatic vessels and somewhere else,
lymphatic tissues and lymphatic organs.
2 Function:
Destroy the invaders, such as
pathogenic orgnisms and other antigens.
Destroy the useless or harmful cells in
human body, such as old RBC, cancertransformed cells, etc.
Lymphocyte
Functionally, lymphocytes can be divided into 3 types:
T cell, B cell and NK cell.
1.T-lymphocyte: educated in thymus and involved in cell-mediated
immune response.
Helper T-lymphocyte----(cluster of the differentiation)CD4+T-lymphocyte.
it can upregulate both cell-mediated immune
HIV
response and humoral immune response;
Cytotoxic T-lymphocyte----CD8+T-lymphocyte. a kind of effector cells
cytotoxic/suppressor T- lymphocyte can
downregulate or turn off immune response
2. B-lymphocyte
B-lymphocyte: educated in the bone marrow and
involved in humoral immune response
Ag
B-lymphocyte
plasma cell
neutralize antigen
antibody
3. Natural killer lymphocyte
NK cell: effector cell.
It can kill abnormal cells directly.
Lymphatic tissue
1.defination: the tissue which is mainly composed of
lymphocytes.
2. classification:(1) diffuse lymphatic tissue
(2) lymph nodule: lymph follicle
（1） diffuse lymphatic
tissue
mainly composed of T lymphocytes
（2） lymph nodule
Also lymphoid follicle,mainly composed of B
lymphocytes.
After stimulation of antigen，the germinal center will
appear.
Classification：primary lymph nodule
secondary lymph nodule
lymphatic nodule: concentration of lymphocytes
contained in the meshwork of reticular cells.
mainly containing B cells together with some
plasma cells, macrophages,etc..
primary nodule: without germinal center;
Ag
Secondary nodule: with germinal center (B cells
proliferates here rapidly).
lymphatic organs
Primary (central) lymphatic organs
---- thymus and bone marrow
----site that T-lymphocytes and B-lymphocytes
get educated respectively.
Secondary (peripheral) lymphatic organs
---- lymph node, spleen and tonsil
---- sites that immune responses are initiated.
1. Thymus
Thymus: capsule ,thymic cortex and medulla
Thymic cortex
Thymic cortex contains thymocytes (more )
and epithelioreticular cells (less).
Thymocytes: developing T-lymphocytes.about
98% of them undergo apoptosis.
Thymic cortex
There are 3 types of epithelioreticular cells in the cortex.
Type I: Located at the boundary of the cortex and capsule.
involved in the formation of blood-thymus barrier.
Type II: Located within the cortex .It is APC
and involved
in thymic cell education
.
Type III: Located at the boundary of the cortex and medulla.
A kinds of APCs to present Ag.
epithelioreticular cells
cortex
thymocytes
（85--90%）
medulla
胸腺高倍
capsule
trabecula
epithelioreticular
cells
thymocyte
Blood-thymus barrier
It is the structure between thymocytes and blood , a
physical barrier to protect developing T-lyphocytes
from exposure to Ag.
Components:
lining endotheium of capillary wall and
its basal lamina;
macrophages in the perivascular C.T.;
type I endothelioreticular cells with
their tight junctions.
Blood-thymus barrier
Thymic medulla
It contains epithelioreticular cells (more) and
T lymphocytes(less).
T lymphocytes here are mature ones.
There have another 3 types of epithelioreticular cells
Type IV: located between the medulla and cortex;
Type V: located throughout the medulla;
Type VI: form the thymic or Hassall’s corpuscles in medulla
Thymic corpuscle
Thymic corpuscle: a characteristic feature of the thymus.
It is a isolated mass of closely packed,
concentrically arranged type VI
epithelioreticular cells .
Found in the thymic medulla.
Function of the thymus
Site of T lymphocyte education
stem cells maturation and
differentiation into T lymphocytes
thymus
2 .Lymph node
The structure of lymph node: capsule ,cortex and medulla
lymph node
Cortex
Cortex consists of superficial cortex, paracortex and sinuses
1. superfacial cortex is organized into nodules, mainly
composed of B-lymphocytes.
It is also bone marrow-dependent cortex.
2. Paracortex is free of nodules, mainly composed of
T-lymphocytes.
It is also thymus-dependent cortex.
3.Sinuses is divided into subcapsular sinuses and trabecular
sinuses where filter the flowing lymph through it.
Lymph node
Specialized high endothelial venules
(HEVs)
Location: in the paracortex
Function: entry of circulating lymphocytes into the
lymph node---enlarging immune response
HEVs
recirculation of of lymphocytes
HEVs
blood vessels
thymu
s
lymph nodes
lymphatic vessels
Bone marrow
lymph node
Medulla
Medulla consists of medullary cords and sinuses.
Medullary cords: cords of lymphatic tissue containing
B cells,plasma cells and macrophages
Medullary sinuses: similar with the sinuses in the cortex
but with more macrophages.
Lymph node
Medullary cord and sinus
Functions of lymph node
（1）filtering lymph；
（2）initiate immune responses.
phagocytosis of macrophage;
B cells proliferate and differentiate into
plasma cells and memory B cells.
3. spleen
the structure of the spleen:capsule,red pulp and white pulp
Capsule of the spleen
Capsule: C.T. containing myofibroblasts, blood vessels,etc.
Red pulp
Splenic sinus
Splenic cord
Cord of lymphatic tissue
with lots of blood cells
spleen
Periarterial lymphatic sheath(PALS)
White pulp
Paracortex in lymph node
Malpighian body（splenic nodule）
Lymphatic nodule in lymph node
capsule
White pulp
trabecula
Red pulp
spleen
White pulp
Malpighian body:
Periarterial lymphatic sheath:
A thick accumulation of lymphocytes
surrounding the artery.
White pulp
White pulp
Malpighian body
PALS
Red pulp
It contains large number of blood cells that it filters
and degrades.
Splenic cord: a meshwork of reticular cells and fibers
containing lots of RBCs, macrophages,
plasma cells,etc.
Splenic sinus: special sinusoidal vessels lined by rodshaped epithelial cells. The processes
of macrophages extend into the sinuses.
red pulp
Splenic cord
Splenic sinus
Splenetic sinusoid
脾
窦
扫
描
电
镜
Function of the spleen
It performs both immune and hemopoietic functions
1. filtering blood: killing pathogenic Ag and destroying
senescent, abnormal RBC ,etc.;
Splenectomy----increasing abnormal RBC in blood
Splenomegaly----malaria
2. initiation of immune responses；
3. formation of blood cells during early fetal life；
4. storage of blood.
spleen
Key points
1.T-lymphocytes get mature in thymus while B-lymphocytes get mature
in the bone marrow.B-lymphocytes can convert to plasma cells
which are responsible for producing Ab.
2. The structure and function of thymus: cortex and medulla . Hassall’s
corpuscle and blood-thymus barrier.
3.The structure and function of lymph node;the celular components of
lymphatic nodule and paracortex.
4.The structure and function of spleen:red pulp and white pulp
( malpighian body and ).
Thymic cortex
There are 3 types of epithelioreticular cells in thymic cortex.
epithelioreticular cells
Type I
Type II
Located at the boundary of the
cortex and capsule.
Serve as a barrier that isolate
thymocytes and C.T.
Located within the cortex .
It is APC with MHC II molecules
which are involved in thymic cell
education.
Type III
Located at the boundary of the
cortex and medulla.
A kinds of APCs to present Ag.
antigen-presenting cell (APC)
1. function：sequestering Ag and presenting
it to helper CD4+T lymphocyte to
facilitate immune responses.
2. components：macrophages,Kuffer cells of liver,
Langerhans’ cells in epidermis,
reticular dentritic cells of spleen
and lymph node,
type II and type III epithelioreticular
cell of the thymus and B lymphocyte
Process of antigen-presenting
MHC (major histocompatability gene complex)
MHC I: expressed on the surface of all
nucleated cells and platelets.
MHC II: expressed on the surface of all APCs.
Circulation in the spleen
Branches of splenic artery enter the white pulp
from trabeculae;
Central artery :sends branches to white pulp
itself and marginal sinuses;
continues to penicillar
arterioles in splenic cord ;
Penicillar arterioles continue with sheathed
capillaries which are empty the blood in the
cord,then the blood cells enter the splenic sinuses.