Antibody production

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T cell and B cell activation

• For Ab production against Antigens

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B cell activation

• Antibody responses to protein antigens require Th
  cells
• Antibody responses to nonprotein antigens dont
  require Th cells

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Th dependent Ab responses to proteins

• Require recognition of the Ag by Th cells and
  cooperation between Ag specific T and B cells
• 1)Ag induced activation of the two cells
• 2)Physical contact between the cells
• 3)Ag presentation by B cells to differentiated Th
• 4) Expression of membrane and secreted molecules
  by the Th cells that bind to and activate the B
  cells

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B cell activation

• Activation of B cells initiated by binding of Ag
  to BCR as a first signal.
• Second signal Signaling by CR2
• B cell receptor serves two key roles in B cell
  activation
• 1)antigen-induced clustering of receptors deliver
  biochemical signals to the B cells that initiate
  the process of activation
• 2)The receptor bind Ag and internalizes it into
  endosomal vesicles for processing and
  presentation

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Functional responses of B cells to Ag recognition

• Ag recognition stimulates the entry of resting
  cells into G1 stage of cell cycle
• Activated B cells express more MHC-II and B7 and
  also cytokine receptors

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T cell activation

• Naïve T cells recognize peptide MHC and are
  activated in peripheral lymphoid organs
  ,resulting in the proliferation and
  differentiation of these cells in to effector and
  memory cells
• Effector helper cells recognize Ag in lymphoid
  organs or other tissues and are activated to
  perform their effector functions
• They secrete cytokines that activate macrophages
  and help B cells
• The activation of T cells requires
• Recognition of peptide MHC complex
• Costimulator
• Cytokines produce by APC and by the T cells
  themselves

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T cell activation

• Earliest detectable responses of T cells to Ag
  recognition is the secretion of cytokines
• Increase their expression of cytokine receptors
• CD69 (bind to sphingosine1 phosphate r.)
• CD25
• CD40L(24-48)
• CTLA-4(24-48)
• CCR7
• CD44

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CD40 CD40L

• Stimulates B cell proliferation and
  differentiation
• Mutation in CD40L gene results in X-linked hyper
  IgM syndrome
• Enhance expression of B7 molecules on B cells
  causing more T cell activation
• Activated Th cells secrete cytokines that act in
  concert with CD40L to stimulate B cell
  proliferation and production of different Ab
  isotypes
• Cytokines serve two principle functions in Ab
  responseB cell proliferation and differentiation
  and switching to different isotypes
• Induce affinity maturation

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Ab response to proteins

• 1)Isotype switching
• 2) Affinity maturation
• 3)Memory cell production
• 4)Prolonged immunity
• 5)More Ab production

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T cell and B cell interaction
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T cell and APC interaction
Adhesion Recognition Activation Costimulation Core
ceptor
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T cell and B cell interaction
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CMI Lab. Diagnosis

• T cell count
• Skin test
• - Tuberculin, PPD
• -LTT (Lymphocyte transformation test)
• MLR (Mixed lymphocyte reaction),
• Lymphokine production
• Lymph node biopsy

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HMI Lab. Diagnosis

• Serum Ig
• B cell count
• Specific Ab
• Plaque forming assay

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WBC Function Tests

• Phagocytic function
• Chemotactic factors
• CMI
• - LTT, LMC, ADCC
• - Skin tests
• HMI
• - Vaccination
• - Plaque forming test
• CBC
• Ig, C3, CH50

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The Phagocytic Function

• Defects of PMN function
• - Defects in the migration cascade
• - Defects in the killing function
• - Defects in both cascades
• Defects of macrophage function
• - Defects in immune response,
  phagocytosis/killing microorganizing antitumor
  activity

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Lab. Evaluation

• 1. Initial screening test CBC/Ig/CH50,C3/Skin
  test
• 2. Specific neutrophil function assay
• Rebuck skin window
• Molecular assay (CD11/CD18 glycoprotein
  def.)
• Chemotaxis assay
• Oxygen burst activity
• Phagocytosis/Intracellular killing
• Degranulation assay
• Neutrophil-mediated antibody dependent
  cellular
• cytotoxicity (ADCC)

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The Lymphocyte Transformation test

• Chronic mucocutaneous candidiasis,
• Congenital or acquired immunodeficiency
  disorders
• To study the integrity of lymphokine
  production,
• Monitor immunosuppressive or immunoenhancing
  therapy,
• Severe combined immune deficiency,
• To predict allograft compatibility in the
  transplantation setting,
• DiGeorge anomaly,
• Nezelof syndrome.

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Why LTT?

• to assess the ability of the lymphocytes to
  proliferate and to recognize and respond to
  antigens

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Types?

• mitogens assay
• using nonspecific plant lectins
• evaluates the mitotic response of T and B
  lymphocytes to a foreign antigen.
• lymphocytes from the patient is incubated with a
  nonspecific mitogen for 72 hours.
• The culture is labeled with tritiated thymidine
• measured by a liquid scintillation
  spectrophotometer in counts per minute,
• antigen assay
• uses specific antigens such as PPD, Candida,
  mumps, tetanus toxoid and streptokinase
• After incubation of 4 ½ to 7 days
• transformation is measured by the same method

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• T cell count
• Skin test
• - Tuberculin, PPD
• -LTT (Lymphocyte transformation test)
• MLR (Mixed lymphocyte reaction),
• Plaque forming assay
• Phagocytic function
• Specific neutrophil function assay
• Neutrophil-mediated antibody dependent cellular
  
• cytotoxicity (ADCC)

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Fusion molecules

• CTLA-4 Ig
• Rheumatoid arthritis
• Transplant rejection
• Psoriasis
• Crohns disease