IMMUNOLOGY

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IMMUNOLOGY
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• An immune system is a collection of mechanisms
  within an organism that protects against disease
  by identifying and killing pathogens and tumor
  cells.

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INTRODUCTION

• INNATE IMMUNITY
• ADAPTIVE IMMUNITY

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Components of Innate Immunity

• Epithelial barriers
• Phagocytic cells
• Natural killer cells
• Plasma proteins
• Proteins of the complement system

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Membrane receptors

• Receptors for mannose residues
• N-formyl methionine containing peptides
• Toll like receptors

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• recognition of microbial structure
• TLRs activate transcription factors(NF-kB)
• NF-kB cytokines
• Reactive oxygen species
• Destruction of microbes

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Components of Adaptive Immunity

• Lymphocytes
• Antibodies

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TYPES OF ADAPTIVE IMMUNITY

• Cell mediated intracellular microbes- T
  lymphocytes (thymus derived)
• Humoral immunity extra cellular microbes - B
  lymphocytes (bone marrow derived)

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T- LYMPHOCYTES

• Antigen presenting cells
• Possess T cell receptors (TCRs)
• Express accessory molecules CD4 CD8
• CD4 bind to Class II MHC molecules
• CD8 bind to Class I MHC molecules
• CD4 helper T cells
• CD6 cytotoxic T cells

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T cell subsets

• T helper cells (also known as effector T cells or
  Th cells) are a sub-group of lymphocytes that
  plays an important role in establishing and
  maximizing the capabilities of the immune system
• These cells are unusual in that they have no
  cytotoxic or phagocytic activity they cannot
  kill infected host cells or pathogens, and
  without other immune cells they would usually be
  considered useless against an infection

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Antigen presentation stimulates T cells to become
either "cytotoxic" CD8 cells or "helper" CD4
cells
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• Cytotoxic T cells destroy virally infected cells
  and tumor cells, and are also implicated in
  transplant rejection. These cells are also known
  as CD8 T cells, since they express the CD8
  glycoprotein at their surface
• Memory T cells are a subset of antigen-specific T
  cells that persist long-term after an infection
  has resolved
• Regulatory T cells formerly known as suppressor T
  cells, are crucial for the maintenance of
  immunological tolerance

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B - LYMPHOCYTES

• B cells are lymphocytes that play a large role in
  the humoral immune response as opposed to the
  cell-mediated immune response that is governed by
  T cells
• Recognize antigen via the B-cell antigen receptor
  complex
• Secrete immunoglobulins

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An antibody is made up of two heavy chains and
two light chains. The unique variable region
allows an antibody to recognize its matching
antigen
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MACROPHAGES

• Part of mononuclear phagocyte system
• Process antigens and present the peptide
  fragments to T cells
• Involved in delayed type of hypersensitivity
  reaction
• Important in effector phase of humoral immunity

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DENDRITIC CELLS

• Interdigitating dendritic cells
• Located under epithelia to easily capture the
  entering microbes
• Express receptors TLRs and mannose for
  capturing and responding to microbes
• Express chemokine receptors ? thus recruited to
  the T- cell zones of lymphoid organs
• Express high levels of MHC class II molecules as
  well as costimulatory molecules B7-1 B7-2

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DENDRITIC CELLS

• Follicular dendritic cells
• Present in the germinal centers of lymphoid
  follicles of spleen, lymph nodes
• Bear Fc receptors for IgG and receptors for C3b ?
  to trap antigen bound to antibodies or complement
  proteins
• Play important role in the pathogenesis of AIDS

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NATURAL KILLER CELLS

• Do not bear receptors / cell surface Ig
• Large granular lymphocytes
• Kill a variety of tumors cells, virally infected
  cells
• Express cell surface molecules CD16 CD56
• Secrete cytokines IFN Gamma, TNF GM- CSF

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CYTOKINES- CLASSIFICATION

• CK that mediate innate immunity IL-1, TNF, type
  1 interferon, IL-6
• CK that regulate lymphocyte growth, activation
  and differentiation IL-2,IL-4,IL-12,IL-15 TGF-B
• CK activate inflammatory cells IFN-G,IL-5, TNF
  and lymphotoxin
• CK that affect leukocyte movement chemokines
  C-C C-X-C
• CK that stimulate hematopoiesis G-CSF, GM-CSF
  

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CYTOKINE PROPERTIES

• Many individual cytokines are produced by
  several different cell types
• Actions are pleotropic
• Induce effects in 3 ways a) autocrine b)paracrine
  c)endocrine
• Mediate effects by binding to high affinity
  receptors on the target

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HISTOCOMPATABILITY COMPLEX

• Also called human leukocyte antigen complex HLA
  complex present on chromosome 6
• Class I- all nucleated cells and platelets
  HLA-a, HLA-B HLA-C
• Class II coded for a HLA-D? DP,DQ,DRhave 2
  alpha and 2 beta chains
• Class III - complement

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CLASS I MHC

• MHC class I molecules are heterodimers,
  consisting of a single transmembrane polypeptide
  chain (the a-chain) and a ß2 microglobulin
• The a chain has three polymorphic domains, a1,
  a2, a3
• Between a1 and a2 is the peptide-binding groove
  which binds peptides derived from cytosolic
  proteins

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CLASS II MHC

• MHC Class II molecules are found only on a few
  specialized cell types, including macrophages,
  dendritic cells and B cells, all of which are
  professional antigen-presenting cells (APCs)
• class II molecules are also heterodimers, but in
  this case consist of two homologous peptides, an
  a and ß chain, both of which are encoded in the
  MHC

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THANK YOU