The document summarizes the key organs, tissues, and cells of the immune system. It describes the primary and secondary lymphoid organs, including the bone marrow, thymus, lymph nodes, spleen, and mucosal associated lymphoid tissues. It also discusses the key immune cells such as B cells, T cells, NK cells, macrophages, dendritic cells, and granulocytes. Finally, it provides an overview of the functions of the immune system, including surveillance, recognition, activation, and effector responses.

1. Bernard S. Bagaya, PhD
Lecturer
Dept. Immun & Mol. Biol
Sch. Biomedical Sciences
MakCHS Organs, Tissues
and Cells of the
Immune
System
Lillian Namuli, MSc.
Teaching Assistant
Immunology

2. • PRIMARY LYMPHOID ORGANS
(Hematopoiesis and antigen independent
lymphocyte maturation)
– Bone Marrow
– Thymus
• SECONDARY LYMPHOID ORGANS
(Antigen dependent lymphocyte
maturation) (e.g an ADAPTIVE immune
response)
- Lymph Nodes
- Spleen
- Mucosal Associated Lymphoid Tissues
(GALT, Peyer’s Patch)

3. The Bone marrow
• Soft tissue in center of
bones
• Site of hematopoiesis in
mammals; all blood cells
originate in the bone
marrow
• Rich in hematopoietic
stem cells – progenitors
of all immune cells
• Site of B cell development

4. The Thymus
• Located behind the
sternum, in front of heart
• Two identically sized lobes
• Larger in childhood, shrinks
in adulthood
• T cell precursors migrate
from bone marrow to
thymus
• Site for T cell differentiation
and maturation
• Also synthesizes hormones
(thymosin, thymolin) that
influence lymphocytes in
blood stream

5. The Lymphatic system
The Lyphatic System
-collects and transports particulates
to lymph nodes for
filtering/sampling

6. Lymph node
- first organized lymphoid
structure to encounter Ag
that enter tissue spaces
- filters tissues

7. The Lymph nodes
• Distributed widely in the body
• Highly packed with lymphocytes (B and T cell follicles),
APCs (Macrophages and Dentritic cells)
• Trap and filter particulates from tissues, hence located
along lymphatic vessels
• Rich network of blood capillaries; bring in and take out
immune cells and effector molecules
• Optimal environment for antigen encounter, antigen
presentation, activation, proliferation, TH cell help
• Cortex (outer layer) is packed with B cells and Germinal
centers (differentiating/proliferating B cells)
• Medulla contains plasma cells secreting antibodies

8. Spleen – filters blood
The spleen

9. The spleen
• Filters particulates in blood
• Consists of the red pulp and white pulp
• White pulp packed with B lymphocytes and T
cells; the PALS contains mostly T-cells
• Antigen activated B cells proliferate and form
Germinal centers in White pulp

10. GALT

14. The Germinal Center (GC)

15. GCs: Site of B cell antigen-dependent proliferation,
somatic hypermutation and affinity maturation
• GCs are anatomically distinct structures within
secondary lymphoid organs
• Formed by packing of rapidly proliferating B
cells
• Rich in antigen/antigen-laden APCs
• Consists of the Light zone and the Dark zone
– Dark zone- rapidly dividing B cells (Centrocytes)
– Light Zone- B cells undergoing affinity selection
(centroblasts), FDCs, Th-cells.

16. Classification of cells
Hematopoietic
stem cells

17. Cells in Innate and Adaptive Immunity

18. Different types of Blood Cells Occur in a Homeostatic state in
blood

19. Lymphoid
Cells

20. Naive lymphocytes (B cells, T cells, NK/Null cells)
look identical (6μm).

21. How can they be distinguished from
each other?
 Cell Surface Molecules
Cluster of Differentiation (CD) e.g CD4, CD8
 Functions (secreting soluble
factors)

22. CD19, B220

23. B cells
- Part of the Adaptive immunity
- Originate/develop in Bone Marrow (humans, mice)
- recognizes antigen directly by cognate interaction with membrane
bound antibody (BCR)
- becomes antibody producing plasma cells or Memory B cell
Memory cells

24. Total B cells: CD45+, B220+, CD19+, CD20+
Naive B cells: CD19+, IgD+/IgM+, CD10+
Mature B cells: CD19+, CD20-, IgG+
Memory B cells: CD19+, CD27+, IgM+
A few B cell markers used in flow cytometry

25. T cells- originates in the BM, matures in the thymus &
circulates via blood to secondary lymphoid organs
- T cells recognize Ag only when it is bound to MHC on
the surface of APC
- CD4 TH cells secrete cytokines
- CD8 TC cells kills aberrant self cells
- Both CD4 TH and CD8 TC cells have long term memory

26. NK cells
• Part of Innate Immunity
•expresses CD16 and CD56 receptors
• Highly Cytotoxic; kills virus infected cells and
tumor cells
• kills antibody bound cells - ADCC
• secrete soluble factors (cytokines) responsible
for immune activation

27. Ly49H
Virus Infected
Tumor cell
Activation of NK cells

28. Antibody Dependent Cellular Cytotoxicity
(ADCC)
IFN-γ

32. Myeloid cells

33. http://www.whfreeman.com/immunology6e/

34. - blood
Granulocyte-monocyte
progenitors (BM)
differentiate into
promonocyte
leave BM to enter into
circulation
differentiate into mature
monocytes
Migrate into tissues to
become tissue-specific
macrophages
resident
wandering
Hematopoeitic Stem
cells (BM)

35. - tissues
1. Phagocytosis
2. Ag presentation
3. Cytokine production

39. Dendritic Cells (DCs)
Antigen presenting cells
• Good at antigen
capturing, Processing,
Presentation
• Secretion of cytokines

40. Myeloid cells
(contd)
- granulocytes

41. - first cells to respond to inflammation
- Excellent at phagocytosis
- Produces chemokines
that attract other cells

42. - antiparasitic, allergy

43. (energy reservoir
for the cell)
- allergic response, heavy metal toxicity

45. Functions of the Immune System
Reconnaissance/Surveillance
Recognition of foreign/abnormal
Activation of mediator
Effector function