T cell and B cell activation For Ab production against Antigens

B cell activation  Antibody responses to protein antigens require Th cells  Antibody responses to nonprotein antigens don’t require Th cells

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

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

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

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: 1) Recognition of peptide –MHC complex 2) Costimulator 3) Cytokines produce by APC and by the T cells themselves

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

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 response:B cell proliferation and differentiation and switching to different isotypes  Induce affinity maturation

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

T cell and B cell interaction

T cell and APC interaction Adhesion Recognition Activation Costimulation Coreceptor

T cell and B cell interaction

CMI Lab. Diagnosis T cell count Skin test - Tuberculin, PPD -LTT (Lymphocyte transformation test) MLR (Mixed lymphocyte reaction), Lymphokine production Lymph node biopsy PC

HMI Lab. Diagnosis   Serum Ig   B cell count   Specific Ab   Plaque forming assay PC

WBC Function Tests   Phagocytic function   Chemotactic factors   CMI : - LTT, LMC, ADCC - Skin tests   HMI - Vaccination - Plaque forming test   CBC   Ig, ‘C3, CH50 PC

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 PC

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) PC

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.

Why LTT?   to assess the ability of the lymphocytes to proliferate and to recognize and respond to antigens

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

  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)

Fusion molecules  CTLA-4 :Ig Rheumatoid arthritis Transplant rejection Psoriasis Crohn’s disease