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T cells. Phenotype, function, fallacies.
Jan Novák
T cells
Central role in the immune system Recognition of antigens Direct effect on the antigens Coordination of the immune response Suppression of the immune responses
T cells versus B cells
Minimal morphological differences
Differentiation based on the detection of surface markers
B cells: CD19, B220, T cells: TCR, CD3, CD4,
CD5, CD8 etc.
Phenotype of T cells
T cell receptor (TCR) Other receptors involved in the antigen recognition
and signalization (CD4, CD8, CD3) Receptors and molecules involved in the migration of
T cells Receptors for cytokines Activation markers (CD25, CD28, CD69)
Groups of T cells
T cells T-helpers (CD4+)
Th1 Th2 Th3
Cytotoxic T cells (CD8+) NKT cells Regulatory T cells (CD4+CD25+)
T cells
CD4+ T lymfocyty – T helpers
IL-12
IL-4
TGF-
Th1
Th2
Th3
Th0 APCTh0
TGF-IL-6
Th17
Th1 cells
Inflammatory cells Help to macrophages
Activation, stimulation of their killing activities Elimination of intracellular agents
Help to T cells Proliferation, Th1 differentiation
Production of cytokines (IFN-TNF-IL-2)
Th1 cells
Clearance of intracellular pathogens
Delayed type of hypersensitivity
Autoimmune diseases
Th2 cells
Help to B cells Development Antibody production
Regulatory functions Production of cytokines (IL-4,IL-5,IL-6,IL-13)
Th2 cells
Defense against extracellular agents
Participation in allergic reactions
Th3
Th3 cells
Develop in the presence of TGF-, IL-10 and IL-4 Secretion of TGF- and IL-10 Induced after oral administration of antigens, play a
role in the induction of oral tolerance
Th3
Th17
Development in the presence of TGF-b a IL-6, IL-21, IL-23
Secretion of IL-17, IL-21, IL-22 Proinflammatory cytokines Role in the immune defense against Klebsiella a
citrobacter Contribution ion the pathogenesis of some organ-
specific autoimmune diseases in experimental model
Th3
Cytotoxic CD8+ T cells
Elimination of dangerous cells of the body Elimination of cells infected by intracellular
pathogens Elimination of stressed cells (tumors,
damaged cells)
Killing by CD8+ T cells
Perforin-granzyme system (degranulation, perforation, apoptotic death)
Fas-FasL interaction (apoptotic death) Cytokine dependent -lymphotoxin (apoptotic
death)
CD8+ T cells in immune reactions
Clearance of infection Onco-immunosurveillance
Regulatory T cells
CD8+ T cells are not supressors!!! CD4+CD25+ T cells Th3 T cells T reg cells NKT cells T cells
Functions of regulatory T cells
Inhibition of the immune responses Maintenance of immunological tolerance Regulation of exagerated reaction against
infection Supresssion of anti-tumor responses
Functions of regulatory T cells
Cell-contact dependent mechanisms Secretion of cytokines (IL-4, IL-10, TGF-) Killing of effector cells
NK cells
NK = natural killer Large granular lymphocytes Development in bone marrow
Immune reactions of NK cells
Functions antigen-non specific Recognition of unknown structures on the
surface of target cells
Immune reactions of NK cells
The function of NK cells is a result of the interaction of their inhibitory and activation receptors
Activation: Fc receptor CD16 ADCC – antibody-dependent cellular
cytotoxicity Inhibition – killer inhibitory receptors (Ly49,
CD94-NKG2)
Immune reactions of NK cells
Cytotoxicity – perforin-granzyme dependent
Immune reactions of NKT cells
Natural Killer T cells Phynotypic and functional features of both NK
and T cells
Immune reactions of NKT cells Natural Killer T cells Phynotypic and functional features of both NK
and T cells Restriction by MHC class I like molecule
CD1d presenting glycolipids and lipids
Phenotype of NKT cells
Expression of TCR, CD3, CD4 Expression of markers of NK lineage Biased TCR repertoire Recognition of conserved glycolipid structure
presented by CD1d
Functions of NKT cells
Secretion of both, Th1 and Th2 cytokines Impact on Th1/Th2 differentiation of naive T cells Activation of B cells Activation of NK cells Activation of dendritic and other ather antigen
presenting cells Cytotoxic functions Regulatory functions
T cells in the development of diseases Defence against infection -
immunodeficiencies Allergic reactions Autoimmunity Oncological diseases
Immunodeficiencies
Primary (SCID, RAG, common chain) Secondary (HIV, tumors, metabolic disorders,
malnutrition, sepsis)
Immunodeficiencies clinical features
Life-threatening – asymptomatic relapsing infections (viruses, fungi, intracellular bacterias)
Human immunodeficiency virus
Retrovirus, RNA virus Targets selectively
CD4+ T cells, macrophages and dendritic cells
HIV infection
1. 3-12 weeks after infection: Flu-like syndrom
2. Asymptomatic period, decrease of CD4+ T cells, production of anti-HIV antibodies
HIV infection
3. AIDS related complex: generalized lymphadenopaty, diarrhoe, candidiasis, fever
HIV infection
4. AIDS: infekce oportunními patogeny pneumocysty, kryptokoky, toxoplazmoza, CMV retinitis, enteritidis, pneumonitis, encefalitis, maligní nádory - Kaposhi sarkom, primární lymfom mozku, NHL B, HIV encefalopatie
Allergic and hypersensitive reactions Type 1 of immunopotahologic reactions Pathological production of IgE antibodies 1.: binding of IgE on mast cells and bazofiles,
degranulation and histamine, bradykinine release oedema
2.: eozinofiles, Th2 cells – secretion of leukotriens a prostaglandines smooth muscle constriction
Participation of Th2 and NKT cells, production of IL-4, IL-13.
Allergic and hypersensitive reactions
Evolutionary – reactions against worms and parazites
Allergic reactions – orms, parazites, dust, food antigens…
Autoimmunity
Reaction of the immune system against body-own tissues
Failure of the immune system to eliminate autoreactive T cells (central, peripheral tolerance).
Autoimmune diseases
Th1 biase of autoreactive T cells Prevention of the disease by Th2 switching Participation of Th1 and CD8+ T cells in
tissue destruction by cytotoxic mechanisms and cytokines
Autoimmunity
Decreased numbers and impaired function of regulatory T cells in experimental animals and patients suffering from autoimmune diseases
Oncoimmunology
The immune system has the capacity to detect and to destroy tumor cells
The animals deficient in T cells develop tumors in increased frequencies
Increased incidence of tumor in immunosupprimed patients
Why immune system does not destroy all tumor cells?
The same HLA phenotype Impaired antigen presentation by tumor cells The selection of less immunogenic cells in the
tumor Production of immunosuppressive factors by
tumor cells
Can we treat oncologic patients by the manipulation of the immune system?
Detection of Tu-specific or Tu-associated antigens CEA, -fetoprotein, MAGE
Can we treat oncological patients by the manipulation of the immune system?
Immunostimulation Vaccines based on
the enhancement of Tu presentation
In vitro expansion of Tu Ag specific T lymphocytes
Vaccines against oncological disorders
Cancer of cervicis uteri Vaccination against papilomaviruses
Literature
Immunobiology – The immune system in health and disease: Charles A. Janeway Jr., Garland Publishing, 2001
The autoimmune diseases: Noel A. Rose, Academic Press – Third edition, 1998
Medical Immunology: Tristam G. Parslow, Lange – Tenth edition, 2001
Nature Reviews Immunology