Lymphoid organs concerned with development and differentiation of lymphocyte.gives specific and non specific immune response against pathogen enters into the body .Lymphoid organs are classified into three categories ;primary lymphoid organs e.g.thymus and bone marrow (involved in lymphocyte development ):secondary lymphoid organs e.g.Lymph nodes ,Spleen,MALT(involved in Ag and lymphocyte interaction and elimination of pathogen).Tertiary lymphoid organs e.g.CALT(import lymphocyte during inflammation ).

1. Organs of immune
system
-Vishakha Guldagad
M.Sc I

2. Content
Lymphoid organs
Classification
Primary lymphoid organs –Thymus , Bone
marrow
Secondary lymphoid organs – Lymph node,
Spleen ,MALT
CALT

3. Lymphoid organs
• Lymphoid organs are stationed throughout the body
• They are concerned with growth ,development and
differentiation of lymphocytes
• There are structurally and functionally divers
lymphoid organs and tissues
• They are interconnected by the blood vesels and
lymphatic vessels though which lymphocyte
circulates
• These organs are involved in specific as well as non
specific immunity

4. Classification
• Based upon the functional development of
lymphatic cells the lymphoid organs are
classified into two groups
a) Primary lymphoid organs
b) Secondary lymphoid organs

6. Primary lymphoid organs
• Also called central lymphoid organs
• It is site for development of immature
lymphocytes
• Organs where differentiation ,proliferation,
and maturation of stem cells into immuno
competent cells take place
• E.g. 1)Thymus
2)Bone marrow

7. Thymus
• Flat ,bilobed organ situated above heart
• Each lobe is surrounded by capsule
• Lobe is divided into lobule and are separated
by connective tissue called trabeculae
• lobule organised into two compartments :
outer – cortex
inner – medullae

9. • The role of thymus in immune function can be
studied by
1) thymectomized mice
2) congenital birth defect –Di George’s
syndrome ,Nude mice .
• Aging is accompanied by a decline in thymatic
function
-experiment thymus grafting in mice

10. Bone marrow
• The site of B cell origin and development
• Have two regions :red bone marrow
:yellow bone marrow
• B cell and Stromal cells within bone marrow
interact with each other and secrete various
cytokines
• Eliminate B cell with self reacting Ab
• In birds – brusa of fabricus

12. Secondary lymphoid organs
• Also called as peripheral lymphoid organs
• It is where Ag is localised so that it can be
effectively exposed to mature lymphocytes
• Initiate adaptive immune response
• E.g. 1) Lymph nodes
2) Spleen

13. Lymphatic system
• A network of vessels that
collect fluid that has escape
into tissue spaces from
capillaries of circulatory
system and ultimately
returns to blood .

14. Lymph nodes
• Where immune response is mounted to Ag in
lymph
• Encapsulated, bean shaped
• First organised structure to encounter Ag
• Divided into 3 concentric regions :
1)cortex
2)paracortex
3)medulla

16. • Cortex - B Cells , Macrophage , Follicular
dendritic cells
-Thymus independent area
• Paracortex -T cells, Macrophage, Dendritic
cells
- Thymus dependent area
• Medulla -plasma cells

17. I. Ag reaches regional node (lymph)
II. It is trapped
III. Class II MHC molecules –Ag( interdigitating
dendritic cells)
IV. Resulting activation of TH
V. Activation of B cells
VI. Initial activation of B cells takes place within
paracortex .B cells differentiate into plasma cell
VII. Secreting IgG

18. Spleen
• Immune response is mounted to Ag in blood
stream
• Large ovoid structure ,situated high left in
abdominal cavity
• Surrounded by capsule- extend interior to form
compartments
• Compartments are of two type –
1) red pulp
2) white pulp

20. • Red pulp : RBC’s , macrophage and few
lymphocytes
-destruction and removal of RBC’s
• White pulp : surrounds splenic artery and
form PALS
-Lymphocytes ,primary follicles present in
PALS rich in B cells
• Marginal zone :lymphocyte ,macrophage

21.  Blood born Ag and lymphocytes
 Spleen
 Marginal zone (trapped by interdigiting
dendritic cells)
 PALS
 Initial activation of B and T cell in –PALS
 Dendritic cell capture antigen
 Combined with MHC molecule and TH cells
 Activates B cells
 Primary follicles in marginal zone

22. Rapidly dividing B cells
Secondary follicles [germinal centre]
Plasma cells – antibody production

23. Mucosal Associated Lymphoid Tissue
• Mucosal membrane have organised lymphoid
tissue known ad MALT
• Less organised : lamina propria (villi )
• Well organised structure: Tonsils ,Appendix
peyer's patches
• Large number of Ab producing plasma cells

24. Tonsils
• Defend against Ag coming from nasal and oral
epithelial routes

25. Gut Associated Lymphoid Tissue

27. Tertiary lymphoid tissue
• Have less cells than secondary lymphoid
organs
• Import lymphoid cells during inflammatory
response
• E.g. Cutaneous Associated Lymphoid Tissue

28. Cutaneous Associated Lymphoid
Tissue
• Skin anatomical barrier
• Have specialised epithelial cells i.e.
Keratinocytes
• Secretes cytokines and express class II MHC
• Langerhans cells (DC) engulf pathogen and
move to lymph node, differentiate into (IDC)
• Further activate TH cells ,clear pathogen

29. References
• Kuby immunology, Judy Owen , Jenni Punt ,
Sharon Stranford., 7th edition (2012)
• https://www.mediacalnewstoday.com/articles
/285666.php

30. Thank you