The document discusses key aspects of immunity and the immune system. It defines immunology as the study of the immune system, including its components, functions, and interactions. The immune system protects the body from pathogens using both innate, nonspecific responses and adaptive, antigen-specific responses. The system includes cells, tissues, organs, and molecular responses. It also outlines the development of the immune system from stem cells and the roles of B cells, T cells, antibodies, and the mechanisms of both humoral and cell-mediated immunity.

1. IMMUNITY

2. Immunology and the Immune system
• Immunology
– The study of the molecular and cellular components
that comprise the immune system, including their
function and interaction, is the central science
of immunology.
• Immune System
– Molecules, cells, tissues and organs which provide non-
specific and specific protection against
• Microorganisms
• Microbial toxins
• Tumor cells
– Crucial to human survival

3. Immune response and Immunity
• Immune response
– Innate (non-specific)
– Adaptive (specific)
• Primary
• Secondary
• Immunity
– State of non-specific and specific protection
• Acquisition of Immunity
– Natural
– Artificial

4. The Immune System
• Human immune system begins to develop in the embryo.
• Starts with hematopoietic (from Greek, "blood-making")
stem cells.
• Stem cells differentiate into major cells in the immune
system
– granulocytes, monocytes, and lymphocytes
• Stems cells also differentiate into cells in the blood that
are not involved in immune function, such as erythrocytes
(red blood cells) and megakaryocytes (for blood clotting).
• Stem cells continue to be produced and differentiate
throughout ones lifetime.

5. Principal function of the Immune system
• To protect humans from pathogenic microorganisms
• Pathogenic microorganisms (Pathogens)
– Microorganisms capable of causing infection and/or disease
• Infection
– Ability of pathogen to enter host, multiply and stimulate an
immune response
• Disease
– Clinical manifestations associated with infection

6. Naturally Acquired immunity
• Active
– Antigens enter body naturally with response of
• Innate and adaptive immune systems
– Provides long term protection
• Passive
– Antibodies pass from mother to
• Fetus across placenta
• Infant in breast milk
– Provides immediate short term protection

7. Artificially Acquired Immunity
• Active
– Antigens enter body through vaccination with response of
• Innate and adaptive immune systems
– Provides long term protection
• Passive
– Antibodies from immune individuals injected into body
• Referred to as
– Immune serum globulins (ISG)
– Immune globulins (IG)
– Gamma globulins
– Provides immediate short term protection

8. Principle mechanisms of
innate and adaptive immunity

10. Innate Immune system
• Innate immunity refers to nonspecific
defence mechanisms that come into
play immediately or within hours of an
antigen's appearance in the body. These
mechanisms include physical barriers
such as skin, chemicals in the blood,
and immune system cells that attack
foreign cells in the body.

11. Cells of innate immunity
NK cells
Dendritic cells
Mast cells
Neutrophils
Monocytes/Macrophages
Phagocytosis, inflammation
Phagocytosis, inflammation,
T-cell activation, tissue repair
Killing of infected or tumor cells
Eosinophils
Inflammation
Defense against parasites
Phagocytosis, activation of naive T-cells
Cell type Pricipal function(s)

12. AntigensAntigens
Some chemical that creates immune response
Most are proteinsproteins or large polysaccharidespolysaccharides
from a foreign organism.
– MicrobesMicrobes: Capsules, cell walls, toxins, viral
capsids, flagella, etc.
– NonmicrobesNonmicrobes: Pollen, egg white , red blood cell
surface molecules, serum proteins, and surface
molecules from transplanted tissue.

13. EpitopeEpitope: AntigensAntigens
Small part of an antigen that interacts
with an antibody. 10-12 amino acids
Any given antigen may have several
epitopes.
Each epitope is recognized by a
different antibody.

14. AntigensAntigens
Some chemical that creates immune response
Most are proteinsproteins or large polysaccharidespolysaccharides from a foreign
organism.
– MicrobesMicrobes: Capsules, cell walls, toxins, viral capsids,
flagella, etc.
– NonmicrobesNonmicrobes: Pollen, egg white , red blood cell
surface molecules, serum proteins, and surface
molecules from transplanted tissue.
– Lipids and nucleic acids are only antigenic when
combined with proteins or polysaccharides.

15. Cont….
• Epitope (Antigenic Determinant)
– Specific site on Ag that is recognized by the
immune system, where Ab binds
• Hapten: Small foreign foreign molecule that is not
antigenic antigenic. Must be coupled to a carrier molecule
to be antigenic. Once antibodies antibodies are formed
they will recognize hapten.
Karl Landsteiner Landsteiner discovered Hapten, who also
discovered blood group antigen and got noble prize.

16. Epitopes: Antigen Regions that
Interact with Antibodies

17. AntibodiesAntibodies
• Proteins Proteins that recognize and bind to a
particular antigen with very high specificityspecificity.
• Made in response to exposure to the
antigen.
• One virus or microbe may have several
antigenic determinant sitesantigenic determinant sites, to which
different antibodies may bind.
• Each antibody has at least two identical
sites that bind antigen: Antigen bindingAntigen binding
sitessites.
• Belong to a group of serum proteins called
immunoglobulins (Igs).immunoglobulins (Igs).

18. Antibody Structure

19. How Do B Cells Produce Antibodies?How Do B Cells Produce Antibodies?
– B cells develop from stem cellsstem cells in the bone marrow of
adults (liver of fetuses).
– After maturation B cells migrate to lymphoid organs (lymph
node or spleen).
– Clonal SelectionClonal Selection: When a B cell encounters an antigen it
recognizes, it is stimulated and divides into many clones
called plasma cellsplasma cells, which actively secrete antibodies.
– Each B cell produces antibodies that will recognize only one
antigenic determinant.

21. Immunoglobulin
• Heavy Chain – 110 amino acids longHeavy Chain – 110 amino acids long
– 100 distinct V segments100 distinct V segments
– 30 D segments30 D segments
– 6 J segments6 J segments
– Enzymes choose one V segment, one D segment and one JEnzymes choose one V segment, one D segment and one J
segment and fuse them togethersegment and fuse them together
– 18,000 combinations in encoding antibody molecule18,000 combinations in encoding antibody molecule
– Splice this variable region to the constant regionSplice this variable region to the constant region
• Light Chain – 211 amino acids longLight Chain – 211 amino acids long
– 10,000 combinations10,000 combinations
– Total of 180,000,000 distinct B cellsTotal of 180,000,000 distinct B cells
• Fusion is sloppy, can create other variantsFusion is sloppy, can create other variants

23. Classes of Antibodies (Immunoglobulins)

24. Immunity and Immune Response
Made up of two cellular systems:
• Humoral or circulating antibody system
– B cells
• Cell mediated immunity
– T cells

25. Overview of the Immune Response

26. Humoral or B-Cell Mediated Immune
Response
Produces secreted antibodies (proteins)
• Bind to antigens and identify the antigen
complex for destruction.
• Antibodies act on antigens in the serum and
lymph
• B-cell produced antibodies may be
– attached to B-cell membranes or
– Free in the serum and lymph.
• Each B lymphocyte makes a unique antibody
molecule (immunoglobulin or Ig)
• Over a million different B lymphocytes are
produced in each individual
– So, each individual can recognize more
than a million different antigens

27. Cell Mediated Immune System:
T lymphocytes
• T-cells mature in the thymus (thus the name T-cell)
• Act on antigens appearing on the surface of individual cells.
• Over a million different kinds of T-cells
– Each produces a different receptor in the cell membrane
– Each receptor is composed of 1 molecule each of two
different proteins
– Each receptor binds a specific antigen but has only one
binding site
– Receptor only recognizes antigens which are
"presented" to it within another membrane protein of
the MHC type (major histocompatibility complex)
• Recognizes specific antigens bound to the antigen-
presenting structures on the surface of the
presenting cell.
• Recognizes antigens presented by B-cells,
macrophages, or any other cell type

28. T Cells and their Functions
• Have a specific receptor for a fragment of antigen
• Cytotoxic T-cells:
– Contain a surface protein called CD8
– Destroy pathogen infected cells, cancer cells, and foreign cells
(transplanted organs)
• Helper T-cells:
– Contain a surface protein called CD4
– Regulate both cellular and humoral immune systems
– This regulation reduces autoimmunity.

29. Central Role of Helper T Cells

30. Cytotoxic T Cells Lyse Infected Cells

31. Antigen-Antibody Interactions
• Quality and quantity are important in resolution of
disease
• May contribute to pathology
• Useful in immunological assays

32. Immune Precipitation
AntigenAntigen
AntibodyAntibody

33. Agglutination
RBC
RBC
RBC
RBC
IgM AntibodyIgM Antibody
IgG AntibodyIgG Antibody
RBC
RBCRBC
RBC RBC
RBCRBC

34. Enzyme (ELISA) Immunoassay
AntigenAntigen
anti-antigen
antibody
Enzyme conjugated to
anti-Ig antibody
(“second antibody”)
Add
substrate
for enzyme