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BIOT 307: MOLECULAR IMMUNOLOGY. Cells and Organs March 7-9, 2011. IMMUNE CELLS. B lymphocytes T “ NK Macrophages Dendritic Cells. Antigen Specific. Antigen-presenting cells (APCs), non-specific. characteristic (See Fig. 2-2) antigen receptors - B, T, NK

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biot 307 molecular immunology

BIOT 307: MOLECULAR IMMUNOLOGY

Cells and Organs

March 7-9, 2011

immune cells
IMMUNE CELLS
  • B lymphocytes
  • T “
  • NK
  • Macrophages
  • Dendritic Cells

Antigen Specific

Antigen-presenting cells (APCs), non-specific

  • characteristic (See Fig. 2-2)
    • antigen receptors - B, T, NK
    • cell surface markers – all
    • functions - all
slide5

LYMPH SYSTEM

  • Multiple functions
  • Branched
  • All tissues of body
  • Lymph vessels & nodes
  • MALT = digestive, respiratory, genitourinary lymphoid tissue, Peyer’s Patches, tonsils, appendix
  • Bone marrow – all long bones
  • Thymus
  • Spleen
hematopoesis

HEMATOPOESIS

DEVELOPMENT OF IMMUNE CELLS

slide11

Bone Marrow

IL1-7, CSF – G, GM, M

C-kit ligand

<----- differentiation

Non-self renewing

Look alike

DNA rearrangements

Thymus

Granulocytes

TH , TC subsets

B cell subsets

Myeloid/Erythroid progenitor

Red cell

b cell development
B-CELL DEVELOPMENT

Naive

Structural and functional changes

Also T-independent activation

Spleen

b cells
B CELLS
  • Move from BM to spleen
    • Marginal zone
    • Mature follicular circulating B cells
  • Ag stimulation  Terminal division into plasma cells  Abs
  • Transitional B cells
    • Naive, non-circulating located in spleen's marginal zone
    • Long-lived follicular B cells = conventional or B2, IgM+, IgD+
b cells1
B CELLS
  • Function = antibody production
  • Activated by Ag
    • TC-dependent and TC-independent
  • Produce Ig (IgG, IgA, IgM, IgD, IgE) of unique Ag specificity
  • Ag recognized is in native/natural, i.e., undigested state
    • Protein, Polysaccharide, Glycolipid, Nucleic acids
  • B Cell Receptors (BCRs) = membrane-bound Ig (antibody) Ag specific molecules
b cells2
B CELLS
  • B cell subsets
    • CD5- = marginal zone B cells
      • Spleen
      • Resting mature B cells
      • Limited repertoire
      • Recognize common bacterial Ag
    • CD5- = B2 B cells conventional (follicular)
      • Major B cell
      • B2 B expresses IgM and IgD
      • 95% recirculating B cells
      • From secondary lymphoid organs
      • Long-lived
      • TC dependent B cell responses to most protein Ag
b cells3
B CELLS
  • B cell subsets
    • CD5+ = B1 B cells
      • 5% of B cell
      • expresses IgM
      • Pleural and peritoneal cavities
      • Self-renewal outside bone marrow
      • Limited ability to rearrange  limited diversity/repertoire
      • Recognize common bacterial Ags, e.g., carbohydrate and lipid
      • Recognition skewed toward TC-independent Ag
      • Not  memory B cells
b cell major surface molecules
B CELL: MAJOR SURFACE MOLECULES
  • Immunoglobulins
    • Clonal selection by Ag
    • 1 antigen determinant per B cell
    • = major B-cell receptor (BCR) molecule
    • Antigen types recognized
      • protein, polysaccharide, glycolipid, and nucleic acids
      • Undigested or natural state
b cell major surface molecules1
B CELL: MAJOR SURFACE MOLECULES
  • Fc receptors
    • Fc = constant region of Ig
    • Modulates events after Ag binds to BCR
  • Complement receptors
    • CR1 (CD-35) and CD2 (CD21) bind certain complement products
    • Enable binding of Ag-Ab-complement complexes
  • Maturation receptor (CD40)
    • Binds to CD40 ligand on T cells
    • Enhances survival and maturation into plasma cells
b cell major surface molecules2
B CELL: MAJOR SURFACE MOLECULES
  • T cell-derived factor receptors
    • CD80 (BC-7), CD-86 (BC-2) on B cells interact with CD28 and CTLA-40 on T cells. CD28 and CTLA-40 are regulatory molecules.
    • On activated B cells
    • Bind to corresponding molecules on T cells (TC-dependent)
  • MHC proteins (Class I and II)
    • Ag presentation to T cells
    • Class II turns B cells into APCs
t cells
T CELLS
  • Only recognize protein antigen in the form of peptides bound to MHC molecules
    • MHC restriction
  • Protein antigen found on APCs
    • B cells, macrophages and dendritic cells
    • Virus-infected cells
    • Graft cells
    • Cancer cells
  • Activated when T cell receptors (TCRs) on T cells recognize
t cell functions
T CELL FUNCTIONS
  • Regulatory, i.e., modulate activities of
    • Other T cells
    • Dendritic cells (DCs)
    • Macrophages
    • B cells
t cell functions1
T CELL FUNCTIONS
  • Mediate CMI through production of cytokines and chemokines
    • Promote proliferation/differentiation of T cells
    • Attract/activate other elements of immune system:
      • inflammation, delayed type hypersensitivity (DTH), resistance to infection by intracellular pathogens
t cell functions2
T CELL FUNCTIONS
  • Interact with and destroy target cells
    • Virus-infected cells
    • Foreign tissues
    • Tumor cells
cells in thymus
CELLS IN THYMUS
  • Maturation
    • Thymic stromal cells release hormones and cytokines and express ligands
  • CD4 and CD8 αβ T cells  CD4+ and CD8+
  • γδ TC 
    • T reg
    • NK
    • Intraepithelial lymphocytes
slide38

MORE NOTES FOR PREVIOUS PAGE: Memory T cell, confer long-term immunity.

Tregs CD4+CD25+, some of which are generated from the thymus, are thought to suppress CD4+ and CD8+ T cells

B-cell development in the bone marrow:

common lymphocyte precursors (CLP)  immature B lineage-committed cells (pro-B)  Ig heavy chain gene rearrangements in pre-B cell stage -->naïve mature B cells leave bone marrow w/ the IgM receptor  secondary lymphoid tissues, where they encounter antigens and are activated; secrete IgM and may isotype switch to IgG. Some differentiate into plasma cells, secreting antigen-specific IgG antibodies essential for long-term immune response.

slide40

NOTES FOR PREVIOUS PAGE: Schematic representation of T cell development. T cells originate from the common lymphoid progenitor cells in the bone marrow. They migrate as immature precursor T cells via the bloodstream into the thymus, which they populate as thymocytes. The thymocytes go through a series of maturation steps including distinct changes in the expression of cell surface receptors, such as the CD3 signaling complex (not shown) and the coreceptors CD4 and CD8, and the rearrangement of their antigen receptor (T cell receptor, TCR) genes. More than 98% of the thymocytes die during maturation by apoptosis (†), as they undergo positive selection for their TCR's compatibility with self-major histocompatibility molecules, and negative selection against those T cells that express TCRs reactive to autoantigenic peptides. In humans, the vast majority of peripheral blood T cells expresses TCRs consisting of α and β chains (αβ T cells). A small group of peripheral T cells bears an alternative TCR composed of γ and δ chains (γ/δ T cells). αβ and γδ T cells diverge early in T cell development. Whereas αβ T cells are responsible for the classical helper or cytotoxic T cell responses, the function of the γδ T cells within the immune system is largely unknown. αβ T cells that survive thymic selection lose expression of either CD4 or CD8, increase the level of expression of the TCR, and leave the thymus to form the peripheral T cell repertoire.Skapenko et al. Arthritis Research & Therapy 2005 7(Suppl 2):S4   doi:10.1186/ar1703

t helper activation
THELPER ACTIVATION
  • MHC II peptide (antigen) complex on APC binds CD4+ and TCR 

proliferation, differentiation 

Ag-specific effector cell clones

  • Type of Ag and APC  activate unique cytokine profiles  3 functional TH types
    • TH1 secrete IFN-γ, IL-2, TNF-β (CMI)
    • TH2 secrete IL-4, 5, 10, 13 (HI)
    • TH17 secrete IL-17 (inflammation)
cd4 t helper
CD4+, THELPER
  • Stimulates B cell antibody production
  • Activates macrophages and TC
  • Maintain memory
  • Main responder to antigens presented by MHC II
    • CD4 binds directly to region of APC’s MHC II molecule
  • Four types based on cytokine secretion and functional activities: TH1, TH2, TH17 and Treg
  • 50-75% T cells
cd8 cytoxic t c
CD8+, CYTOXIC (TC)
  • Kill virus-infected cells, transplanted tissue, cancer cells
  • Two mechanisms:
    • Bind to cell surface and inject perforin and granzymes
    • Bind to Fas ligands  apoptosis
cd8 cytoxic t c1
CD8+, CYTOXIC (TC)
  • Naive TC activation involves
    • co-stimulation by DCs/cytokines
    • Proliferate when TCR recognizes foreign processed (peptide) Ag associated with MHC I (cross-presentation)
  • Effector cells secrete IFN-γ
  • Subsets according to cytokines secreted
  • Class 1 MHC restricted
  • 20-40% T cells
t reg
TREG
  • Suppressor TC
  • CD4+, CD25+ (IL-2 receptor α chain), FOX P3+ expressing FOXP3 – transcription factor
  • = 5-10% T cells
  • Prevent autoimmune disease
  • Diminish effector responses to cancer and infections
slide50
γδ+ TC
  • CD4-, CD8-, CD3+
  • Function in innate manner
  • Generate memory
  • Less TCR diversity but TCR genes rearrange
  • Recognize phosphorylated microbial molecules and lipid antigens not presented by MHC – soluble molecules
  • Gut mucosa
  • IFN-γ, THF-α