The immune system consists of central immune organs like the bone marrow and thymus where immune cells develop and peripheral organs like the lymph nodes and spleen where immune responses occur. The bone marrow generates lymphocytes and the thymus matures T cells. Lymph nodes filter antigens from lymph and mount immune responses while the spleen filters blood and traps antigens. Mucosal tissues associated with the gut, lungs and skin also contain lymphoid tissues that initiate immune responses to pathogens at barrier sites. Together these organs circulate and mature immune cells throughout the body to provide defenses against foreign invaders.

1. Lecture 2-Advanced Immunology
Dr. Yasra Sarwar
Organs of Immune System

2.  Functional system
rather than organ
system
 Hematopoetic
 Vasculature
 Lymphatics
Immune System

3. ➢ Immune organs and immune tissues
1. Central immune organs (primary lymphoid organs)
2. Peripheral immune organ (secondary lymphoid organs)
3. Tertiary lymphoid tissues
➢ Immunocytes
1. Lymphocytes (T, B cells and NK cells)
2. APC (Macrophages, DC, B cells)
3. Other cells (neutrophil, basophil, eosinophil etc.)
➢ Immune molecules
Antibody, Complement, Cytokine
CD and adhesion molecules, MHC molecules
Components of Immune System

5. Primary/central immune organs are the sites of
generation, differentiation and maturation of
immunocytes.
1. Bone marrow
2. Thymus
3. Bursa of Fabricius
(the site of B cells maturation in birds)
Primary Immune organs

6. 1. Bone marrow
• Most of the lymphocytes arise here
• T cells arise and mature in thymus to
mature
• B cells arise and mature in bone marrow
• 90% of plasma IgG and IgA comes from B
cells in the bone marrow
Primary Immune organs

7. ➢The site of generation of immunocytes
➢The site of differentiation and maturation of
immunocytes
➢The site of immune response of B cell,
specifically in secondary immune response.
Functions of bone marrow

8. 2. Thymus
➢ Site of T cell development and
maturation
Structure
1. Bilobed organ above heart
2. Surrounded by capsule and
divided into lobules
3. Outer part of lobule is cortex,
inner is medulla
4. Network of epithelial cells,
dendritic cells, and macrophages
Primary Immune organs
THYMUS

9. The structure of Thymus

11. (1) Thymus stromal cells (TSC)
Thymus epithelial cells (TEC),
Fibrocyte, Macrophages, Dendritic
cells
(2) Thymocytes
The cells migrate from the bone
marrow to the thymus and then
become thymocytes
Cells in thymus and thymus
microenviroment

12. 1. Development and differentiation of T
lymphocytes in thymus
2. TSC interact with thymocytes directly by
adhesion molecules.
3. TSC secrete various cytokines and thymus
hormones.
4. Thymocytes secrete various cytokines.
5. Immune regulation of the thymus
3. Function of Thymus

13. ➢Specific immune organs in birds
➢The site of differentiation and proliferation of
B cells in birds.
Bursa (Bursa of Fabricius)

14. Lymphatic System
• The part of the circulatory system that is concerned
especially with scavenging fluids and proteins which
have escaped from cells and tissues and returning
them to the blood, with the phagocytic removal of
cellular debris and foreign material, and with the
immune response.
• It consists especially of lymphoid tissue, lymph, and
lymph-transporting vessels

15. Lymphatic System
 Interstitial fluid (the portion that doesn’t enter
venous system) is returned to circulatory system
by lymphatic vessels
 Largest lymphatic vessel – thoracic duct
○ Enters left subclavian vein
○ Lymph from right arm and right side of head
enters through right lymphatic duct, drains
into right subclavian
 Antigen is carried by lymph to lymph nodes

17. Thoracic
duct
Overview of blood and lymph system and how
leukocytes travel from one system to another
Site of exchange between the
blood and lymph systems
Lymph carrying antibodies
and immune cells collect in
thoracic duct where the
lymph empties back into the
blood circulatory system

18. Overall view of the lymph system,
showing the locations of major organs
The circulatory system is the means by
which cells of the immune system
directly or indirectly interact with all
of the cells of the body
Lymph nodes: contain high
concentrations of leukocytes that filter
out microbes and toxins
Spleen of the blood circulatory system
has the same function as the lymph
nodes
Lymph nodes and spleen can
sometimes become infected by the
organisms that have collected during
filtration

19. Secondary Lymphoid Organs
Lymph Nodes
 Encapsulated
 3 regions:
1. Cortex
 B cells, macrophages,
dendritic cells
 Primary follicles
2. Paracortex
 T cells, dendritic cells
3. Medulla
 Plasma cells secreting antibody

22. ➢Filter and eliminate foreign antigens.
➢The site of immune response.
➢The site of lymphocytes residence and source of
recirculation cells.
Functions of lymph nodes

23. Secondary Lymphoid Organs
Spleen
 Filters blood, traps blood-borne antigens
 Important in systemic infections
 Blood enters through splenic artery
 Encapsulated

24. Structure:
Projections from capsule form
trabeculae dividing it into
compartments.
Two main parts:
1. Red pulp
Macrophages, red
blood cells
2. White pulp
-Surrounds branches of
splenic artery
-Forms PALS (periarteriolar
lymphoid sheath)
-Primary follicles rich in B
cells

25. ➢The site of immunocytes residence.
➢The site of immune response.
➢Produce some active substances, such as
complement.
➢Function of filtration.
Functions of spleen

26. Lymphoid Tissues
1. Mucosa-Associated Lymphoid Tissue (MALT)
Organized in areas along digestive, respiratory, and urogenital tracts
 Very well organized areas in intestine are referred to as Peyer’s
patches
 Includes tonsils and appendix
The mucosal surfaces of the gastrointestinal and respiratory tracts
are colonized by lymphocytes and APCs that initiate immune
responses to injested and inhaled antigens.

27. 1. Gut-associated lymphoid tissue (GALT)
⚫ M cell: membranous epithelial cell
---antigen transporting cell
2. Nasal-associated lymphoid tissue (NALT)
3. Bronchial-associated lymphoid tissue (BALT)
Distribution of MALT

31. II. 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

32. ➢ The first line of defense against foreign antigen.
➢ The site of immune response.
➢ Participate in delayed hypersensitivity.
Functions of MALT and SALT

33. Thymus
Peyer’s
patches
(small
intestine)
Appendix
(cecum)
Adenoid
Tonsils
Lymphatic
vessels
Spleen
Lymph
nodes
Lymph
node
Blood
capillary
Interstitial
fluid
Tissue
cells
Lymphatic
vessel
Lymphatic
vessel
Masses of
defensive cells