As a periodontist, I have included the basics of immunity from the periodontist point of view that will help in understanding the immunological basis of periodontal disease...

2. Dr. Kritika Jangid
MDS- Periodontics

3.  IMMUNITY: Resistance to infectious disease
 IMMUNE SYSTEM: Collection of cells,
tissues and molecules that mediate resistance
to infections
 IMMUNE RESPONSE: Coordinated reactions
of these cells and molecules to infectious
microbes
 IMMUNOLOGY: Study of immune system
and its response to invading pathogens

4. Role of the Immune System
• Defence against infections
• Recognises and responds to
tissue grafts and newly
introduced proteins
• Defence against tumors
Implications
• Deficient immunity results
in increased susceptibility
to infections. Vaccination
boosts immune defences
and protects against
infections
• Immune responses are
barriers to transplantation
and gene therapy
• Potential for
immunotherapy for cancer

9.  Also calledNaturalor Nativeimmunity.
 Components present before the onset of infection.
 Disease resistantmechanismsthatare not specificto a
particularpathogen
 Pathogensmust first breach barriers thatprotect host

10.  Provides the first line defence right after exposure.
 Most micro-organisms are readily cleared within a
few days by innate immune system before
adaptive immune system is activated

11.  Componentsofinnateimmunityrecognizestructuresthatare sharedby
variousclassesofmicrobesandare notpresentonthehostcells
 Foreg: Phagocytesexpressreceptorsfor
1. Bacterial LPS(endotoxin)-On cellwallofmany bacterialspecies
2. Terminalmannoseresidues-Typicalofbacterialgylcoproteins
3. DsRNA-Foundinviruses
4. UnmethylatedCpGoligonucleotide-CommoninmicrobialDNA

12. PATHOGEN ASSOCIATED MOLECULAR
PATTERNS:
The microbial molecules that are targets of
innate immunity .
Indicates that they are shared by microbes of
the same type
PATTERN RECOGNITION RECEPTORS:
The receptors of innate immunity that recognize
the shared structures.

13.  Recognizes structures of microbes that are often essential
for the survival and infectivity of these microbes.
 Recognize molecules that are released from stressed or
necrotic cells. (Damage associated molecular patterns)
 Does not react against the host
 Encoded in the germline; not produced by somatic
recombination of genes
 Two principal types of defences are:
1. Inflammation
2. Antiviral defence

16. EPITHLIAL
BARRIERS
PHAGOCYTES
DENDRITIC
CELLS
NK CELLS
OTHER
LYMPHOCYTES
COMPLEMENT
CYTOKINES
PLASMA
PROTEINS

18.  2 types: Neutrophils and monocytes recruited to the
site of infection where they recognize and ingest
microbes for intracellular killing.
 NEUTROPHILS (PMNs): MACROPHAGES

19.  PMNs
 Most abundant leukocytes (4000-10,000/µL)
 Infection: 20,000µL of blood
 1st cell type to respond to most infections (particularly
bacterial and fungal)
 Stimulated by cytokines (Colony stimulating factors)
which act on the bone marrow stem cells to produce
neutrophil precursors
 Ingest microbes in the circulation and rapidly enter
extravascular tissues at the site of infection where they
ingest microbes and die after a few hours.

20.  500-1000/µL of blood
 Monocytes that enter extravascular tissues survive in
these sites for long periods

22. Phagocytosis
and
intracellular
killing of
microbes

23.  Initiate T- cell responses
 Important bridge between
innate and adaptive immunity
 Respond to microbes by
producing cytokines that
recruit leukocytes and initiate
adaptive immune responses

26.  γδ T cells: Present in epithelia
 NK-T cells: Present in epithelia and lymphoid organs.
(Recognize microbial lipids bound to a class 1 MHC-
related molecule called CD1)
 B-1 cells: Most of the antibodies are specific for
carbohydrates that are present in the cell walls of many
bacteria.
 Marginal zone B cells: Responses that are characteristic of
adaptive immunity (eg. Antibody production) and have
features of innate immunity (eg. Rapid responses and
limited diversity of antigen recognition)

27.  Collection of circulating and membrane associated
proteins.
 Complement activation involves the sequential
activation of proteolytic enzymes sometimes called an
enzymatic cascade.
 3 pathways:
 Alternative pathway
 Classical pathway
 Lectin pathway

29.  Secreted in small amounts in response to an external
stimulus and bind to high affinity receptors on target
cells

31.  MBL: Plasma Mannose binding lectin:
 Recognizes microbial carbohydrates and can coat
microbes for phagocytosis or activate the complement
cascade by lectin pathway.
 Belongs to collectin family of proteins which shares
homology to collagen and contain a carbohydrate
binding (lectin) domain.
 CRP: Binds to phosphoryl-choline on microbes and
coats the microbes for phagocytosis.

34.  Triggered only if microbes or their
antigens pass through epithelial
barriers and are delivered to the
lymphoid organs where they can be
recognized by lymphocytes.

35.  Specialized to combat different types of infections:
 Antibodies: Eliminate microbes in extracellular fluids
 Activated T lymphocytes: Eliminate microbes living
inside cells

37.  Protection from an infectious disease
agent that is mediated by B- and T-
LYMPHOCYTES following exposure to
specific antigen, and characterized
by IMMUNOLOGIC MEMORY.

38.  Active immunity: Immunity induced in an
individual by infection or vaccination
 Passive immunity: Immunity conferred in
an individual by transfer of antibodies or
lymphocytes from an actively immunized
individuals

41.  Antigen receptors of B lymphocytes (Membrane
bound antibodies) can recognize a wide variety of
macromolecules (proteins, polysaccharides, lipids and
nucleic acids) as well as small chemicals in soluble or
cell surface associated form.
 Most T lymphocytes can see only peptide fragments of
protein antigens, and can do so only when these
peptides are presented by specialized peptide display
molecules on host cells

43.  Majority of T lymphocytes recognize peptide
antigens that are bound to and displayed by major
histocompatibility complex (MHC) molecules of
antigen presenting cells (APCs)

44.  Capture of
protein
antigens by
antigen
presenting
cells (APCs)

45.  Antigen Presentation to T
cells
 MHC (major histocompatibility
complex) 1
 all nucleated cells
 MHC-encoded alpha (hvy)
chain and beta 2 (lt)
microglobulin
 Polymorphic alpha 1 and alpha
2 domains for closed binding
cleft
 Conserved alpha 3 domains =
binding site for CD8
 Beta 2 interacts noncovalently
with alpha 3

46.  MHC-II = dimer of alpha
and beta subunits
 APCs
 Both chains MHC
encoded
 Alpha 1 and beta 1
domains variable and form
open binding cleft
 Most of variability on
beta chain
 Alpha 2 and beta 2 folded
into Ig domains
 B2 Ig domain binds to
CD4

47.  FEATURES OF
PEPTIDE
BINDING TO
MHC
MOLECULES

49.  T cells can be distinguished by their different antigen
receptors
 The definitive T cell linage marker is the T cell antigen
receptor (TCR).
 2 different types of TCR are:
 A heterodimer of two disulfide- linked polypeptides (α
and β)
 A structurally similar heterodimer consisting of γ and δ
polypeptides
90-95% of blood T cells are αβ T cells

50.  There are 3 major subpopulations of αβ T cells
 Helper T cells (TH) that expresses the CD4 marker
(CD4+ T cells) and mainly ‘helps’ or ‘induces’ immune
responses
 TH1 cells secrete IL2 and IFN γ
 TH2 cells produce IL4. IL5, IL6 and IL10
 Regulatory T cells (Treg) that expresses the CD4+ T cells
and regulate immune responses.
 Cytotoxic T cells (TC) that express the CD8+ T cells- also
called as cytotoxic T lymphocytes (CTLs)

51.  Initiation of T cell responses requires multiple
receptors on the T cells recognizing ligands on the
APCs:
 The TCR recognizes MHC associated peptide antigens,
CD4 and CD8 c0-receptors recognize the MHC
molecules strengthen the binding of T cells to APCs, and
receptors for co-stimulators recognize second signals
provided by the APCs
 The molecules other than antigen receptors that are
involved in T cell responses to antigens sometimes are
called Accessory molecules of T lymphocytes

53.  Humoral immunity is mediated by antibodies and is
the arm of adaptive immune response that functions
to neutralize and eliminate extracellular microbes and
microbial toxins
 More important in defending against microbes with
capsules rich in polysaccharides and lipids and against
polysaccharide and lipid toxins

56.  PLASMA B CELLS
 MEMORY B CELLS
 B1 CELLS
 B2 CELLS

57.  B cell activation
Antibody Forming Cells
Plasma Cells

58.  glycoprotein molecules that are produced by plasma
cells

60.  Major Ig in serum
 Crosses the placenta
 Macrophages, monocytes, PMNs and some
lymphocytes have Fc receptors for the Fc region of IgG.
 Opsonin

62.  Third most common serum Ig
 Good complement fixing Ig
 Good agglutinating Ig
 IgM exists as a monomer and lacks J chain

64.  2nd most common serum Ig.
 Major class of Ig in secretions - local (mucosal)
immunity.
 Does not fix complement, unless aggregated.
 IgA can binding to some cells - PMN's and some
lymphocytes.

66.  IgD is found in low levels in serum
 IgD is primarily found on B cell surfaces
 IgD on the surface of B cells has extra amino acids at
C-terminal end for anchoring to the membrane. It also
associates with the Ig-alpha and Ig-beta chains.
 IgD does not bind complement

68.  IgE is the least common serum
 Involved in allergic reactions - various
pharmacological mediators that result in allergic
symptoms.
 IgE also plays a role in parasitic helminth diseases.
Eosinophils have Fc receptors for IgE and binding of
eosinophils to IgE-coated helminths results in killing
of the parasite.
 IgE does not fix complement.

72.  Basic Immunology 3e By: Abbas and Lichtman
 Immunology 8e By: Roitt et. al.
 Carranza’s Clinical Periodontology 10e, 11e