1. Introduction to Cellular Immunology
Dr. Colin R.A. Hewitt
Movie credits:
The movies of cells are used with the permission of
Dr. James A. Sullivan of Cells Alive

2. The purpose of this preliminary lecture is to remind students of the immunology learnt in the second year, and introduce key concepts that are required for a full understanding of the later lectures
To use the lecture, click on the projection screen icon below , then just click your way through the presentation.
Don’t forget to try the online multiple choice questions at the end to find your strengths and weaknesses

3. What you should know by the end of this lecture
 The basic terms used in immunology
 The characteristics and interdependence of adaptive and innate immunity
 The names and functions of cells in the immune system
 The structure and function of peripheral lymphoid organs
The purpose of lymphocyte recirculation
 How cells communicate in the immune system and how this is tested
 How the clonal distribution of antigen receptors in the immune system allows for diverse recognition, self tolerance and memory
 That the compartments invaded by pathogens require different effector mechanisms of immunity.

4. History & impact of immunology on human health
1700
1900
1800
2000
Jenner
Vaccination
1600
Jansen
Microscope
Müller
Bacteria
Koch’s
Postulates
Metchnikoff
Phagocytosis
Wright
Antisera
Kohler & Milstein
Monoclonal Abs
1955
Miller
T cells
1965
1970
1975
1980
Countries with
more than one
smallpox case
per month 30 15
200 years
after Jenner
WHO announce
smallpox eradicated

5. Why study immunology now?
Infectious diseases
Mechanisms of pathogenicity
Vaccine development
Diseases caused by a disturbed immune system
ALLERGY: Immune responses to innocuous materials e.g. ASTHMA
AUTOIMMUNITY: Anti-self immunity e.g. MULTIPLE SCLEROSIS
GRAFT REJECTION: Immune responses to TRANSPLANTED TISSUE
IMMUNODEFICIENCY: Defects in immune responses e.g. SCID
Manipulation of immunity to treat disease
IMMUNOSUPPRESSION: Treatment of immune diseases
IMMUNOREGULATION: Immunotherapeutic interventions

6. Reminder of basic immunological terms
ANTIGENS (Ag)
are substances recognised by
• ANTIBODIES (Immunoglobulin, Ig, Ab) and
• T LYMPHOCYTES (T CELLS)
Antibodies are made by
B LYMPHOCYTES (B CELLS)
T cells help B cells make antibodies:
T HELPER (Th) cells
T cells kill infected cells
T CYTOTOXIC (CTL)

7. Cellular and humoral defences
Immune responses
Invasion
& infection
Barriers
Innate immunity
Adaptive immunity +
Inflammation
Skin & Mucous membranes
rapidly regenerating surfaces, peristaltic movement, mucociliary escalator, vomiting, flow of urine/tears, coughing
Cellular and humoral defences
lysosyme, sebaceous/mucous secretions, stomach acid, commensal organisms,complement proteins, phagocytosis, NK cells
Cellular and humoral defences
Antibodies, cytokines, T helper cells,
cytotoxic T cells

8. Immunity established to adapt to infection
Adaptive immunity
Immunity established to adapt to infection
• Learnt by experience
• Confers pathogen-specific immunity
• Enhanced by second exposure
• Has memory
• Uses cellular and humoral components
• Is poorly effective without innate immunity
Antibodies reflect infections to which an
individual has been exposed- diagnostic for infection

9. Innate immune response Inbuilt immunity to resist infection
• Present from birth
• Not antigen-specific
• Not enhanced by second exposure
• Has no memory
• Uses cellular and humoral components
• Is poorly effective without adaptive immunity
Also involved in the triggering and amplification of adaptive immune responses

10. Leucocytes Adaptive and innate immunity depends upon LEUCOCYTES
Innate immunity is mediated largely by GRANULOCYTES
Adaptive immunity mediated by LYMPHOCYTES
The growth, development and activities of granulocytes and lymphocytes are interconnected and often co-operative.

11. Cells Of The Immune System
Lymphocyte Adaptive immunity
Macrophage
Monocyte
Neutrophil
PMN
Eosinophil
Basophil
Mast cell
Phagocytosis
Ag presentation
Phagocytic
Anti-bacterial
Anti-parasite
immunity
?Protection of
mucosal surfaces?
Protection of
mucosal surfaces
Common
lymphoid
progenitor
Myeloid
Pluripotent
haemopoietic
stem cell

12. CLP T B Th CTL PC Lymphocyte subsets Common lymphoid precursor T CELLS
B CELLS
Activate B cells
and macrophages
T HELPER CELLS Th
Kill virus-
infected cells
CYTOTOXIC T
LYMPHOCYTES
CTL
Produce antibodies
PLASMA CELLS PC

13. Cytotoxic T- lymphocyte killing target
Look for some excellent low power images and electron micrographs of the cells at the following site:
Resting Lymphocyte
Activated Lymphocyte
Plasma cell
T and B cells are morphologically identical
Movie:
Cytotoxic T- lymphocyte killing target
(click on this link)

14. Human macrophage ingesting Candida albicans
Look for some excellent low power images and electron micrographs of the cells at the following site:
Erythrocyte (Red blood cell)
Blood monocyte
Platelet (thrombocyte)
Tissue macrophage
Movie:
Human macrophage ingesting Candida albicans
(click on this link)

15. Chemotaxis of human neutrophils
Look for some excellent low power images and electron micrographs of the cells at the following site:
Neutrophil
Movie:
Chemotaxis of human neutrophils
(click on this link)

17. Look for some excellent low power images and electron micrographs of the cells at the following site:
Eosinophil
Basophil
Neutrophil
Lymphocyte
Monocyte

18. Lyc B T Lymphocyte antigen receptors
Until the 1960’s, lymphocytes had no known function.
T and B cells are essentially inactive until they
encounter antigen.
T and B cells express ANTIGEN RECEPTORS
Lyc B
The B cell antigen receptor is a membrane-bound antibody
SURFACE IMMUNOGLOBULIN T
The T cell antigen receptor IS NOT membrane bound antibody but a distinct molecule
T CELL ANTIGEN RECEPTOR
Each antigen receptor binds to a different antigen
Each cell has only one antigen specificity

19. Lymphoid organs
Organised tissue in which lymphocytes interact with non lymphoid cells
Sites of maturation & initiation of adaptive immune responses
CENTRAL LYMPHOID ORGANS
PERIPHERAL LYMPHOID ORGANS
Central lymphoid organs:
THYMUS – T cell maturation
BONE MARROW – B cell maturation
Peripheral lymphoid organs:
LYMPH NODES
SPLEEN WHITE PULP
MUCOSAL-ASSOCIATED LYMPHOID TISSUE
T and B cell activation
Antigen trapping

20. Lymph node 4. Germinal centre (site of intense B cell proliferation)
5. Medullary cords
(Macrophage &
plasma cell area)
3. Secondary
lymphoid follicle
6. Efferent lymphatic
vessel
2. Primary Lymphoid
follicle (B cell area)
Artery
Paracortical
(T cell) area
Vein
1. Afferent lymphatic
vessel. Lymph, cells
& Ag drained from
tissues enters here
Medullary sinus

21. Look for an excellent image of a sectioned lymph node at the following site:

22. Look for an excellent image of a germinal centre at the following site:

23. Spleen white pulp Transverse section Marginal sinus B cell corona
Red pulp
Germinal centre
Marginal zone
Periarteriolar lymphocytic
sheath (PALS) – T cell area
Central arteriole

24. Look for an excellent image of a sectioned spleen at the following site:

25. Lymphocyte recirculation
NAIVE LYMPHOCYTES enter
blood, are seeded to the
peripheral lymphoid organs
and recirculate
Cells & antigens from a site of infection
are trapped in draining lymphoid tissue.
Cells proliferate and re-enter the
RECIRCULATING LYMPHOCYTE POOL
to re-seed the peripheral lymphoid organs

26. Look for an excellent images of Wuchereria bancrofti and elephantiasis at the following site:

27. How immune cells communicate:
SOLUBLE MEDIATORS
Infection
Phagocyte
activation
CYTOKINES & CHEMOKINES
Diverse collection of soluble proteins made by cells that affect the behaviour of other cells. The balance & level of cytokines and chemokines secreted affects the outcome of the response
INFLAMMATION
Early events involve endothelial cells and result in the accumulation of fluid, plasma proteins & leucocytes.
Later events involve the activation and maturation of lymphocytes and other granulocytes.

28. Bio-assay of cytokines in vitro
Activation
of M in vitro
Test for effect
on other
cells
Cytokine secretion
+/-
Remove cytokine containing supernatant
Which cytokine?

29. Specificity of cytokine bioassays
Test for a characteristic
effect on other cells
e.g. interleukin-1
Induces proliferation in thymocytes
Include an antibody that blocks interleukin-1 + +
IL-1 absent -
IL-1 present

30. How immune cells communicate:
CELL-CELL CONTACT
Peripheral lymphoid tissues trap antigen-containing phagocytic cells and concentrate cells together to promote cell-cell contact.
Cell-cell contact occurs at many stages of immune responses. T
CTL
Target cell
Killing T
Accessory cell activation
Antigen
presentation B Y
Ab production

31. Cell surface molecules mediate cell-cell contact
Resting cells
Activated cells
Expression and level of expression controls cell-cell adhesion
Activation can induce expression.
Cell adhesion, migration, antigen specificity, antigen presentation,
costimulation, helper function, effector function.
Cell surface molecules influenced by activation include cytokine receptors.

32. Bio-assay of cell cell contact requirements in vitro
Physically
separate
cells with permeable
membrane T
Include a blocking
anti-MHC molecule antibody +
Due to cytokine
or cell-cell contact? T T +
MHC molecules not important T -
Not due to a cytokine
Which cell surface molecule? -
MHC molecules important

33. Clonal nature of the adaptive immune response
Each lymphocyte expresses a single antigen receptor specificity.
There are millions of lymphocytes in the body, and thus millions of different antigen receptors.
Each naive lymphocyte bearing a unique receptor is the progenitor of a genetically identical CLONE of daughter cells.
PROBLEM: The CLONAL DISTRIBUTION of antigen receptors means that lymphocytes of a particular specificity will be too infrequent to mount an effective response.
A process akin to natural selection, CLONAL SELECTION raises the clonal frequency of cells with a particular antigen specificity

34. Clonal selection theory: MacFarlane Burnet 1957
Daughter cells bear identical antigen specificity to the parent cell.
Each lymphocyte bears a single type of receptor of unique specificity.
Antigen interaction leads to lymphocyte activation.

35. Clonal selection induces proliferation
and increases effector cell frequency
No. of cell divisions
No. of
cells with
useful
specificity
Threshold of
protective effector
function

36. Clonal nature of adaptive immune response
allows for removal of harmful cells
Opportunity to remove harmful specificity at an early stage of development
IMMUNOLOGICAL TOLERANCE
!!!!Cells specific for self antigen!!!!
Antigen receptors recognising self antigens can be individually purged from the antigen receptor REPERTOIRE before clonal expansion

37. Clonal nature of adaptive immune response
allows for immunological memory 4 16 12 8 20 64 68 72
Antibody
titre
Days
2° response
to antigen A
1° response
to antigen B
Lymphocyte
proliferation
to Ag B
Lymphocyte
proliferation
to Ag A
1° response
to antigen A
Lymphocyte
apoptosis A A B

38. Immune effector mechanisms against extracellular pathogens & toxins
NEUTRALISATION Y ` Y ` Y ` Y `
Adhesion to
host cells blocked
Prevents
invasion
Toxin release
blocked
Prevents
toxicity
NEUTRALISING ANTIBODIES

39. Effector mechanisms against extracellular pathogens
OPSONISATION
Bacteria in extracellular space Ab +
Fc receptor
Phagocytosis
OPSONISATION
binding

40. Effector mechanisms against extracellular pathogens
COMPLEMENT
Bacteria in plasma
Lysis
binding
Ab &
COMPLEMENT +
Phagocytosis
Complement &
Fc receptor
Opsonisation

41. Effector mechanisms against intracellular pathogens
CYTOXICITY
CTL
CTL
CTL
Target cell
death
Viral infection
Lethal hit

42. Th Th Effector mechanisms against intracellular bacteria
MACROPHAGE ACTIVATION
Inflammatory
T cell Th
Cytokines Th
Activation of killing mechanisms
Activated macrophage
Resting Macrophage

43. NOW TRY THE MULTIPLE CHOICE QUESTIONS
Summary:
 Reminder of 2nd year immunology
 Characteristics and components of adaptive and innate immunity
 Peripheral lymphoid organs & lymphocyte recirculation
 Intercellular communication by cytokines and cell-cell contact
 Clonal selection: Ag recognition, self tolerance and memory
Effector mechanisms
NOW TRY THE MULTIPLE CHOICE QUESTIONS
(click on this link)