Cells of the immune system can be categorized as cells of the innate immune system or cells of the adaptive immune system. Cells of the innate immune system include phagocytes such as macrophages, neutrophils, dendritic cells, and basophils and mast cells. Cells of the adaptive immune system include lymphocytes such as B cells and T cells. B cells are involved in antibody production while T cells include cytotoxic T cells and helper T cells that activate other immune cells. Natural killer cells are also lymphocytes that help identify and destroy tumor or virus infected cells.

1. Immunology Lecture 3rd
Cells of Immune System
BY
Dr. Humera Kausar
22th
Sep 2014

2. Cells of the Immune System

3. Cells of the Immune System
Leucocytes

4. Cells of the innate immune system:
• Phagocytes
– Monocytes/macrophages
– Neutrophils/PMNs/
• NK cells
• Basophils and mast cells
• Eosinophils

5. Phagocytic Cells Mononuclear
PROMONOCYTES
MONOCYTES
MACROPHAGES (Fixed or Free)
Brain ---------Microglial cells
Lungs ------------Alveolar cells
Liver ----------------- Kupffer cells
Connective tisues-----Histocytes
Kidney ---------------------Mesangial cells
Bones ------------------------ Osteoclasts
Skin ------------------------Langerhans cells

6. Macrophages
• Characteristic nucleus
• lysosomes
• CD14 membrane
marker protein
Macrophage

7. Macrophages
Activated by variety of stimuli in the course of an
immune response.
Activated macrophages are more effective then
resting ones in eliminating potential pathogen.
Activated macrophages secreted various cytotoxic
proteins that help to eliminate broad range of targets
including
o virus infected cells
o Tumor cells
o Intracellular bacteria
 Also act as antigen presenting cells

8. Macrophage as an antigen presenting cells

9. Granulocytes
Neutrophils
Polymorphonuclear (PMN) leukocyte.
 Has multilobed nucleus and granulated cytoplasm.
 Stains with both acidic and basic dyes.
 Constitute 50% to 70% of the circulating
leukocytes.
 After release in to the blood, circulates 7 –10 hours
before migrating in to the tissues.
 Life span is few days. (3 days)

10. Neutrophils (PMNs)
• CD66 membrane
marker protein
Geimsa stains
Neutrophil

11. Neutrophils
First cells to arrive at the site of inflammation.
 In response to many types of infections the bone
marrow releases increased number of circulating
neutrophils called leukocytosis.
Act as phagocytic cells.
GRANULOCYTES

12. Neutrophils GRANULOCYTES
Lytic enzymes and bactericidal substances in
neutrophils are contained within primary and
secondary granules.
 Larger denser primary granules are a type of
lysosome containing
peroxidase, lysozyme, various hydrolytic enzymes
 Smaller secondary granules contains,
collagenases, lactoferrin, lysozyme
 Both primary and secondary granules fuse with
phagosomes.

13. Neutrophil

14. Eosinophils
Stain with acid dye eosin red.
Has bilobed nucleus and granulated cytoplasm.
Constitute 1% to 3% of WBC population.
 Like neutrophils, motile phagocytic cells that can
migrate from blood into tissues.
 Phagocytic role of eosinophils are less significant
than that of neutrophils.
 Play a role in the defense against parasitic organisms
by secreting contents of eosinophilic granules, which
damage the parasite membrane.
GRANULOCYTES

15. Eosinophil

16. Basophils
 Basophil has a lobed nucleus and heavily granulated
cytoplasm.
 Stains with basic dye methylene blue.
 Non phagosytic granulocyte.
 Constitute <1% of circulating WBC.
 Function by releasing pharmacological active
substances from cytoplasmic granules.
 Play a major role in certain allergic responses.
GRANULOCYTES

17. Basophil

18. Mast Cells
 By hematopoiesis, released into the blood as
undifferentiated cells.
 Do not differentiate until they leave the blood and
enter the tissues, including
skin, connecting tissue of various organs,
mucosal epithelial tissues of respiratory, genitourinary
& digestive tracts
 Like circulating basophils, mast cells have large
numbers of cytoplasmic granules that contains
histamines and other pharmacological active substances.
 Play an important role in the development of allergies.

19. MEDIATORS RELEASED
Prostaglandin D2
Platelet Activating Factor
Tryptase
Heparin
Histamin
IL-4, IL-5, IL-6, IL-8
TNFɑ

20. CAUSING
Vasodilation,
increased vasopermeability,
contraction of smooth muscles,
bronchoconstriction,
increased eosinophil, neutrophil & monocyte
chemotaxis,
anticoagulation,
increased fibroblast proliferation,
platelet activation

21. Dendritic Cells
Activation of T cells and
initiate adaptive immunity
Found mainly in lymphoid
tissue
Function as antigen
presenting cells (APC)
Most potent stimulator of
T-cell response

22. Dendritic Cells

23. Dendritic Cells
DC covered with long membranous extensions
that resemble the dendrites of nerve cells.
 Display class I & class II MHC.
B and T lymphocytes are the mediators of
immunity, but their function is under the control
of dendritic cells.
 Dendritic cells in the periphery capture and
process antigens.

24. Dendritic Cells
 Express lymphocyte co-stimulatory molecules,
(B7, CD40)
 Migrate to lymphoid organs and secrete
cytokines to initiate immune responses.
 They not only activate lymphocytes, they also
tolerize T cells to antigens that are innate to the
body (self-antigens), thereby minimizing
autoimmune reactions.

25. Cells of the immune system:
APC
• Cells that link the innate and adaptive arms
– Antigen presenting cells (APCs)
• Heterogenous population with role in innate immunity
and activation of Th cells
• Rich in MHC class II molecules
– Examples
• Dendritic cells
• Macrophages
• B cells
• Others (Mast cells)

26. Cells of Adaptive Immune
System
T cells and B cells

27. Cells of the Adaptive Immune System:
• Lymphocytes (Lymphoid Cells)
– B cells
• Plasma cells (Ab producing)
• Memory cells
– T cells
• Cytotoxic (CTL)
• Helper (Th)
– Th1
– Th2
– Null cells (NK cells)

28. Lymphoid Cells
 Contributes 20-40% of body’s WBCs,
Naïve or unprimed cells are small, motile, non-
phagocytic cells.
 Can not be distinguished morphologically.
 Resting cells are in G0 phase of cell cycle.
 Small lymphocytes are 6 um in diameter.
 Cytoplasm barely covers the rim around
nucleus.

29. Lymphoid Cells
 Have,
o densely packed chromatin
o few mitochondria
o poorly developed endoplasmic reticulum
o Golgi apparatus
 Life span of effector cell is few days to few
weeks.

30. B-Lymphocytes
Derived its name from its site of maturation in the
Bursa of fabricius in birds and Bone marrow in humans
•Plasma cells (Ab producing)
•Memory cells

31. B-CELL RRECEPTORS
Membrane bond Ig molecules
i.e.,1.5 x 105
molecules/cell
CD 45 (Marker B220)
MHC II (Antigen Presenting
receptor)
CD35(Complement receptor)
CD21(Complement receptor)
CD32(Fc RII)ɤ

32. T-CELL RRECEPTORS
TCR
Thy 1 (1st
receptor remains
throughout life span of the cell)
CD4 (T- helper cell)
CD8 (T- cytotoxic cell)
Ratio of Th : Tc = 2:1

33. T- helper cell vs T cytotoxic cell)

34. Specificity of adaptive immune
response
• Resides with Ag
Receptor on T and B
cells
• TCR and BCR – both
specific for only ONE
antigenic determinant
• TCR is monovalent
• BCR is divalent
T cell
TCR Ag
B cell
BCR
Ag
Ag

36. Cytotoxic T cells (Tc) and Class I MHC proteins
The cell-cell interaction between
the infected cell and the Tc
cell is mediated by the
MHC/antigen complex and TCR
The Tc cell produces cytotoxic proteins
perforins—produce holes or pores in the
target cell and granzymes enter the
virus infected cell causing apoptosis or
programmed cell death
The cytotoxic proteins only affect those
cells to which the Tc cell has specifically
interacted

37. T helper cells and (TH) Class II MHC proteins
Specialized TH cell involved in
the inflammatory response
Cell-cell interaction mediated
by the TCR and the class II
MHC-antigen complex activates
The TH cell which produces
cytokines
TNF-alpha (tumor necrosis factor)
IFN-gamma (interferon)
GM-CSF (granulocyte-monocyte
colony stimulating factor)
These cytokines further stimulate
macrophages to increase phagocytic
activity and to in turn produce cytokines
that promote inflammation

38. NATURAL-KILLER CELLS
 Fails to express membrane molecules that
distinguished B and T cells.
 Fails to express antigen binding receptors.
 Constitute 5% - 10% of lymphocytes in human
peripheral blood.
 NK cells have ability to recognize tumor or
virus infected cells.
 NK cells express membrane receptor CD16 for
a specific region of antibody molecule (ADCC).

39. NATURAL-KILLER CELLS

40. Human red blood cells
(red), activated platelets
(purple) and white blood
cells - monocyte (green)
and T lymphocyte
(orange).
Colorized-SEM
(scanning electron
micrograph)
Magnification:-1200x--
(Based on an image
size of 1 inch in the
narrow dimension)
Cells of the Immune System

41.
‫پیدا‬ ‫سے‬ ‫مٹی‬ ‫تمہیں‬ ‫نے‬ ‫جس‬ ‫ہے‬ ‫وہی‬ ‫ا‬
‫اس‬ ‫اور‬ ‫دیا‬ ‫کر‬ ‫مقرر‬ ‫وقت‬ ‫ایک‬ ‫پھر‬ ‫کیا‬
‫بھی‬ ‫پھر‬ ‫تم‬ ‫ہے‬ ‫مقرر‬ ‫مدت‬ ‫ایک‬ ‫کےہاں‬
‫ہو‬ ‫کرتے‬ ‫شک‬)2(
‫عام‬َ ‫لن‬‫ٴ‬ ‫ا‬ ‫ة‬ُ ‫ر‬َ ‫و‬ۡ ‫س‬ُ