Lecture 7 BIOL 533 1
Interactions of Phagocytes and
Other Immunological Cells
BIOL 533
Lecture 7
Medical Microbiology
Lecture 7 BIOL 533 2
Production of Ab and Activation of
Macrophages and Cytotoxic T Cells
? T-Dependent
? T-Independent
Lecture 7 BIOL 533 3
T-Dependent Activation
? Extracellular pathogens
– Digested by macrophage—Ag complexed MHC
class II (present only in macrophage and few
other cell types)
– Stimulates helper T cells (TH2) to find B cells,
recognize particular peptide fragment?Ab
– Helper T cells (CD4+ cells; TH1) produces
IFN? and activates macrophage
Lecture 7 BIOL 533 4
T-Dependent Activation
? Intracellular pathogens
– Digested when released from dying host cell
– Peptide Ag presented on MHC class I
– Proliferation of cytotoxic T cells (CD8+)
Lecture 7 BIOL 533 5
Processing CHO and Lipid Ag
? LPS interacts directly with B cells
(independent of T cells)
? CHO Ag largely independent of T cells,but
some involvement (production of
cytokines; necessary for maximal B cell
activity)
Lecture 7 BIOL 533 6
T-Dependent Mechanism
? Macrophage presents part of Ag and own
class II MHC to T-helper cell (signal #1)
? Also makes IL1 6 (signal #2)
– IL1 6 stimulates T cell clone to divide and
make IL2 4-6
– IL1 also stimulates hypothalamus to raise
body temperature,enhancing T cell action
Lecture 7 BIOL 533 7
T-Dependent Mechanism
? IL2 4-6 stimulate T-helper cells to multiply
– These T cells associate with B cells that have
correct Ag— MHC II complex and secrete B
cell growth factors (BCGF) that cause B cells
to multiply
Lecture 7 BIOL 533 8
T-Dependent Mechanism
? The number of B cells increase,T-helper
cells produce other cytokines (BCDF)
– These cause some B cells to stop dividing,
differentiating into plasma cells and produce
Ab
– Also B cell recognizes its Ag through its
surface IgM receptor (signal #1 for B cell),
subsequently triggered to proliferate?plasma
cells?Ab
Lecture 7 BIOL 533 9
T Cell Biology
? MHC molecules
– Major Histocompatibility Complex
– Found on plasma membrane
– Class I found on most nucleated body cells
– Class II found only on leukocytes involved in
immune response (macrophage,Ag-
presenting cells,B cells)
– Class I and II Ag processed differently
Lecture 7 BIOL 533 10
T Cell Biology
? Class I molecules bind to peptides found
in cytosol (e.g.,replicating viruses)
? Endogenous proteins are digested by
natural processes
? Peptides from cytosol?endoplasmic
reticulum
Lecture 7 BIOL 533 11
T Cell Biology
? Within ER,class I MHC heavy chain
synthesized and associates with ?2
microglobulin
? Dimer binds peptide ?plasma membrane
? If peptide is foreign,passing CD8+ T cell
(cytotoxic) recognizes,releases cytokines,
destroys cell
Lecture 7 BIOL 533 12
T Cell Biology
? Class II MHC bind to fragments arise from
exogenous Ag
? Peptide recognized by CD4+ T-helper cells
? Do not directly kill cell
– cells enlarge and divide?more CD4+ cells
– Secrete cytokines (such as IL2) either directly
inhibit pathogen or recruit other cells for
immune response
Lecture 7 BIOL 533 13
MHC Genetics
? MHC gene complex located chromosome 6
? ABCD co-dominant
? Individuals may have any combination of
8 different MHC molecules
? One gene of each pair code for MHC
Lecture 7 BIOL 533 14
MHC Genetics
? Types of Genes
– Class I ABC
– Class II D
– Class III
? Encode second component of complement (C2)—
classical pathway
? Factor B—alternate pathway
? Two forms; 4th complement components (C4a
C4b)
Lecture 7 BIOL 533 15
Regulator T Cells
? T-helper CD4+
– TH1,IL2,IFN?,TNF; macrophage activation
– TH2,IL 4,5,10,13; humoral immunity
– TH0,not much known
? T-suppressor
Lecture 7 BIOL 533 16
Regulator T Cells
? T-helper,two signals for stimulation by Ag
– Ag fragments presented to T cell by
macrophage,dendritic,or activated B cell +
MHC class II; needed for recognition by T-cell
receptor and CD4 protein on surface TH1 cell
– CD28 protein receptor on TH1 cells
? CD28 binds to CD80 on macrophage?2nd signal;
both go into cytoplasm of TH1 cell
Lecture 7 BIOL 533 17
Regulator T Cells
? Signal 1 activates tyrosine kinase
– Adds phosphate groups to tyrosine in proteins
? Enzyme phospholipase C?I cleaves phosphatidyl
inositol bisphosphate in T cell helper membrane
? Two cleavage products; two pathways
– First diacyl glycerol activates protein kinase C
? Protein kinase C moves into nucleus catalyzes
formation protein complex AP1
Lecture 7 BIOL 533 18
Regulator T Cells
– Second,inositol triphosphate causes Ca
channel to open; Ca++ ions rush in cytosol;
activation of calmodulin,calcineurin,and
nuclear factor of activated TH1
Lecture 7 BIOL 533 19
Regulator T Cells
? NF-AT?nucleoplasm binds to AP-1
NF-AT/AP-1 (transcription factor)
? Transcription factor binds to DNA specific
gene sequence,IL2 m-RNA transcribed
? IL2m-RNA?ribosomes where IL2 protein
produced
Lecture 7 BIOL 533 20
Regulator T Cells
? Signal 2 mediated
– CD28 receptor plus CD80 molecule activates
another tyrosine kinase?formation
transcription factor CD28RC; also stabilizes
IL2 m-RNA; increases concentration of IL2
– TH1 cells activated by 2 signals secrete large
amounts of IL2?activates cytotoxic T cells
Lecture 7 BIOL 533 21
Regulator T Cells
? Signal 2 mediated,cont’d,
– Also secrete IFN? which activates
macrophages and enhances antimicrobial
activity
– TH2 cells costimulated by Ag presentation and
IL1,then release several cytokines that
stimulate B cell proliferation and
differentiation into Ab forming plasma cells
Lecture 7 BIOL 533 22
Cytotoxic T Cells CD8+
? Destroy target cells
– CD95 pathway (fas gene produces; apoptosis
sequence)
– Perforin pathway?direct cytolysis; secretion
of perforin and granzyme proteins
Lecture 7 BIOL 533 23
Cytotoxic T Cells CD8+
? CD95 Pathway
– CD95 transmembrane fas protein receptor
found in many eukaryotic cells
– CD95 coded fas gene; member of TNF family
of genes
– Fas ligand binds
? CD95/CD95L complex activates several cytosolic
proteins?cellular suicide sequence
Lecture 7 BIOL 533 24
Cytotoxic T Cells CD8+
? Perforin pathway
– Ca+2 dependent sequence
? Microtubule assembly
? Movement of cytoplasmic granules
? Reorientation of Golgi apparatus
? Movement of microtubule organizing center
– T cell secretes pore-forming protein perforin
– T cell secretes granzymes (proteolytic
enzymes further damage it),cause cytosis
Lecture 7 BIOL 533 25
Lecture 7
? Questions?
? Comments?
? Assignments..,
Interactions of Phagocytes and
Other Immunological Cells
BIOL 533
Lecture 7
Medical Microbiology
Lecture 7 BIOL 533 2
Production of Ab and Activation of
Macrophages and Cytotoxic T Cells
? T-Dependent
? T-Independent
Lecture 7 BIOL 533 3
T-Dependent Activation
? Extracellular pathogens
– Digested by macrophage—Ag complexed MHC
class II (present only in macrophage and few
other cell types)
– Stimulates helper T cells (TH2) to find B cells,
recognize particular peptide fragment?Ab
– Helper T cells (CD4+ cells; TH1) produces
IFN? and activates macrophage
Lecture 7 BIOL 533 4
T-Dependent Activation
? Intracellular pathogens
– Digested when released from dying host cell
– Peptide Ag presented on MHC class I
– Proliferation of cytotoxic T cells (CD8+)
Lecture 7 BIOL 533 5
Processing CHO and Lipid Ag
? LPS interacts directly with B cells
(independent of T cells)
? CHO Ag largely independent of T cells,but
some involvement (production of
cytokines; necessary for maximal B cell
activity)
Lecture 7 BIOL 533 6
T-Dependent Mechanism
? Macrophage presents part of Ag and own
class II MHC to T-helper cell (signal #1)
? Also makes IL1 6 (signal #2)
– IL1 6 stimulates T cell clone to divide and
make IL2 4-6
– IL1 also stimulates hypothalamus to raise
body temperature,enhancing T cell action
Lecture 7 BIOL 533 7
T-Dependent Mechanism
? IL2 4-6 stimulate T-helper cells to multiply
– These T cells associate with B cells that have
correct Ag— MHC II complex and secrete B
cell growth factors (BCGF) that cause B cells
to multiply
Lecture 7 BIOL 533 8
T-Dependent Mechanism
? The number of B cells increase,T-helper
cells produce other cytokines (BCDF)
– These cause some B cells to stop dividing,
differentiating into plasma cells and produce
Ab
– Also B cell recognizes its Ag through its
surface IgM receptor (signal #1 for B cell),
subsequently triggered to proliferate?plasma
cells?Ab
Lecture 7 BIOL 533 9
T Cell Biology
? MHC molecules
– Major Histocompatibility Complex
– Found on plasma membrane
– Class I found on most nucleated body cells
– Class II found only on leukocytes involved in
immune response (macrophage,Ag-
presenting cells,B cells)
– Class I and II Ag processed differently
Lecture 7 BIOL 533 10
T Cell Biology
? Class I molecules bind to peptides found
in cytosol (e.g.,replicating viruses)
? Endogenous proteins are digested by
natural processes
? Peptides from cytosol?endoplasmic
reticulum
Lecture 7 BIOL 533 11
T Cell Biology
? Within ER,class I MHC heavy chain
synthesized and associates with ?2
microglobulin
? Dimer binds peptide ?plasma membrane
? If peptide is foreign,passing CD8+ T cell
(cytotoxic) recognizes,releases cytokines,
destroys cell
Lecture 7 BIOL 533 12
T Cell Biology
? Class II MHC bind to fragments arise from
exogenous Ag
? Peptide recognized by CD4+ T-helper cells
? Do not directly kill cell
– cells enlarge and divide?more CD4+ cells
– Secrete cytokines (such as IL2) either directly
inhibit pathogen or recruit other cells for
immune response
Lecture 7 BIOL 533 13
MHC Genetics
? MHC gene complex located chromosome 6
? ABCD co-dominant
? Individuals may have any combination of
8 different MHC molecules
? One gene of each pair code for MHC
Lecture 7 BIOL 533 14
MHC Genetics
? Types of Genes
– Class I ABC
– Class II D
– Class III
? Encode second component of complement (C2)—
classical pathway
? Factor B—alternate pathway
? Two forms; 4th complement components (C4a
C4b)
Lecture 7 BIOL 533 15
Regulator T Cells
? T-helper CD4+
– TH1,IL2,IFN?,TNF; macrophage activation
– TH2,IL 4,5,10,13; humoral immunity
– TH0,not much known
? T-suppressor
Lecture 7 BIOL 533 16
Regulator T Cells
? T-helper,two signals for stimulation by Ag
– Ag fragments presented to T cell by
macrophage,dendritic,or activated B cell +
MHC class II; needed for recognition by T-cell
receptor and CD4 protein on surface TH1 cell
– CD28 protein receptor on TH1 cells
? CD28 binds to CD80 on macrophage?2nd signal;
both go into cytoplasm of TH1 cell
Lecture 7 BIOL 533 17
Regulator T Cells
? Signal 1 activates tyrosine kinase
– Adds phosphate groups to tyrosine in proteins
? Enzyme phospholipase C?I cleaves phosphatidyl
inositol bisphosphate in T cell helper membrane
? Two cleavage products; two pathways
– First diacyl glycerol activates protein kinase C
? Protein kinase C moves into nucleus catalyzes
formation protein complex AP1
Lecture 7 BIOL 533 18
Regulator T Cells
– Second,inositol triphosphate causes Ca
channel to open; Ca++ ions rush in cytosol;
activation of calmodulin,calcineurin,and
nuclear factor of activated TH1
Lecture 7 BIOL 533 19
Regulator T Cells
? NF-AT?nucleoplasm binds to AP-1
NF-AT/AP-1 (transcription factor)
? Transcription factor binds to DNA specific
gene sequence,IL2 m-RNA transcribed
? IL2m-RNA?ribosomes where IL2 protein
produced
Lecture 7 BIOL 533 20
Regulator T Cells
? Signal 2 mediated
– CD28 receptor plus CD80 molecule activates
another tyrosine kinase?formation
transcription factor CD28RC; also stabilizes
IL2 m-RNA; increases concentration of IL2
– TH1 cells activated by 2 signals secrete large
amounts of IL2?activates cytotoxic T cells
Lecture 7 BIOL 533 21
Regulator T Cells
? Signal 2 mediated,cont’d,
– Also secrete IFN? which activates
macrophages and enhances antimicrobial
activity
– TH2 cells costimulated by Ag presentation and
IL1,then release several cytokines that
stimulate B cell proliferation and
differentiation into Ab forming plasma cells
Lecture 7 BIOL 533 22
Cytotoxic T Cells CD8+
? Destroy target cells
– CD95 pathway (fas gene produces; apoptosis
sequence)
– Perforin pathway?direct cytolysis; secretion
of perforin and granzyme proteins
Lecture 7 BIOL 533 23
Cytotoxic T Cells CD8+
? CD95 Pathway
– CD95 transmembrane fas protein receptor
found in many eukaryotic cells
– CD95 coded fas gene; member of TNF family
of genes
– Fas ligand binds
? CD95/CD95L complex activates several cytosolic
proteins?cellular suicide sequence
Lecture 7 BIOL 533 24
Cytotoxic T Cells CD8+
? Perforin pathway
– Ca+2 dependent sequence
? Microtubule assembly
? Movement of cytoplasmic granules
? Reorientation of Golgi apparatus
? Movement of microtubule organizing center
– T cell secretes pore-forming protein perforin
– T cell secretes granzymes (proteolytic
enzymes further damage it),cause cytosis
Lecture 7 BIOL 533 25
Lecture 7
? Questions?
? Comments?
? Assignments..,
