T cell and B cell activationT cell and B cell activationFor Ab production against For Ab production against

AntigensAntigens

B cell activationB cell activation

Antibody responses to protein antigens Antibody responses to protein antigens require Th cellsrequire Th cells

Antibody responses to nonprotein antigens Antibody responses to nonprotein antigens don’t require Th cellsdon’t require Th cells

Th dependent Ab responses to Th dependent Ab responses to proteinsproteins

Require recognition of the Ag by Th cells and Require recognition of the Ag by Th cells and cooperation between Ag specific T and B cellscooperation between Ag specific T and B cells

1)Ag induced activation of the two cells1)Ag induced activation of the two cells

2)Physical contact between the cells2)Physical contact between the cells

3)Ag presentation by B cells to differentiated Th3)Ag presentation by B cells to differentiated Th

4) Expression of membrane and secreted 4) Expression of membrane and secreted molecules by the Th cells that bind to and molecules by the Th cells that bind to and activate the B cellsactivate the B cells

B cell activationB cell activation

Activation of B cells initiated by binding of Ag to Activation of B cells initiated by binding of Ag to BCR as a first signal.BCR as a first signal.

Second signal: Signaling by CR2Second signal: Signaling by CR2 B cell receptor serves two key roles in B cell B cell receptor serves two key roles in B cell

activation:activation:1)antigen-induced clustering of receptors deliver 1)antigen-induced clustering of receptors deliver

biochemical signals to the B cells that initiate the biochemical signals to the B cells that initiate the process of activationprocess of activation

2)The receptor bind Ag and internalizes it into 2)The receptor bind Ag and internalizes it into endosomal vesicles for processing and endosomal vesicles for processing and presentationpresentation

Functional responses of B cells to Functional responses of B cells to Ag recognitionAg recognition

Ag recognition stimulates the entry of Ag recognition stimulates the entry of resting cells into G1 stage of cell cycleresting cells into G1 stage of cell cycle

Activated B cells express more MHC-II Activated B cells express more MHC-II and B7 and also cytokine receptorsand B7 and also cytokine receptors

T cell activationT cell activation

Naïve T cells recognize peptide –MHC and are activated in Naïve T cells recognize peptide –MHC and are activated in peripheral lymphoid organs ,resulting in the proliferation and peripheral lymphoid organs ,resulting in the proliferation and differentiation of these cells in to effector and memory cellsdifferentiation of these cells in to effector and memory cells

Effector helper cells recognize Ag in lymphoid organs or other Effector helper cells recognize Ag in lymphoid organs or other tissues and are activated to perform their effector functionstissues and are activated to perform their effector functions

They secrete cytokines that activate macrophages and help B cells They secrete cytokines that activate macrophages and help B cells The activation of T cells requires:The activation of T cells requires:

1)1) Recognition of peptide –MHC complex Recognition of peptide –MHC complex

2)2) CostimulatorCostimulator

3)3) Cytokines produce by APC and by the T cells themselvesCytokines produce by APC and by the T cells themselves

T cell activationT cell activation

Earliest detectable responses of T cells to Ag recognition is the Earliest detectable responses of T cells to Ag recognition is the secretion of cytokinessecretion of cytokines

Increase their expression of cytokine receptorsIncrease their expression of cytokine receptors CD69 (bind to sphingosine1 –phosphate r.)CD69 (bind to sphingosine1 –phosphate r.) CD25CD25 CD40L(24-48)CD40L(24-48) CTLA-4(24-48)CTLA-4(24-48) CCR7CCR7 CD44CD44

CD40 – CD40LCD40 – CD40L

Stimulates B cell proliferation and differentiationStimulates B cell proliferation and differentiation Mutation in CD40L gene results in X-linked hyper IgM Mutation in CD40L gene results in X-linked hyper IgM

syndromesyndrome Enhance expression of B7 molecules on B cells causing Enhance expression of B7 molecules on B cells causing

more T cell activationmore T cell activation Activated Th cells secrete cytokines that act in concert Activated Th cells secrete cytokines that act in concert

with CD40L to stimulate B cell proliferation and with CD40L to stimulate B cell proliferation and production of different Ab isotypesproduction of different Ab isotypes

Cytokines serve two principle functions in Ab response:B Cytokines serve two principle functions in Ab response:B cell proliferation and differentiation and switching to cell proliferation and differentiation and switching to different isotypesdifferent isotypes

Induce affinity maturationInduce affinity maturation

Ab response to proteinsAb response to proteins

1)Isotype switching1)Isotype switching

2) Affinity maturation2) Affinity maturation

3)Memory cell production3)Memory cell production

4)Prolonged immunity4)Prolonged immunity

5)More Ab production5)More Ab production

T cell and B cell interactionT cell and B cell interaction

T cell and APC interactionT cell and APC interaction

Adhesion

Recognition

Activation

Costimulation

Coreceptor

T cell and B cell interactionT cell and B cell interaction

CMI Lab. Diagnosis T cell countSkin test - Tuberculin, PPD -LTT (Lymphocyte transformation test)MLR (Mixed lymphocyte reaction), Lymphokine productionLymph 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, phagocytosi

s/killing microorganizing antitumor activity

PC

Lab. Evaluation

1. Initial screening test : CBC/Ig/CH50,C3/Skin test2. 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 moleculesFusion molecules

CTLA-4 :IgCTLA-4 :Ig

Rheumatoid arthritisRheumatoid arthritis

Transplant rejectionTransplant rejection

PsoriasisPsoriasis

Crohn’s diseaseCrohn’s disease