CYTOKINES/CYTOKINE RECEPTORS
Ch.8:15-8:29 Janeway/Travers Ch 12, Abbas Text
I. Methods of Cell Communication -- concept of the "immunological synapse".
A. Cognate - cell/cell contact
B. Non-Cognate - "soluble messengers"
1. Reality is mixture of both
2. Initially termed "factors"; i.e. TCGF, BCGF
a. Lymphokine - "lymphocyte moving molecules"
b. Monokine - "monocyte moving molecules"
c. Cytokine - "cell moving molecules"
d. Interleukins (IL) - "molecules that move between cells"
(1) To get IL - must be cloned/well characterized -- presently up to IL-
18; along with a variety of others that retained original names
(2) Probably about a dozen will cover the majority of important
activities since there is considerable overlap, i.e. "backup"
3 General properties of cytokines
a. Pluripotent molecules which almost invariably have a wide range of activities on
diverse cell types
b. Produced during the effector phases of natural and specific immunity  mediate
and regulate immune and inflammatory responses.
c. Produced during the effector phases of natural and specific immunity  mediate
and regulate immune and inflammatory responses.
d. Often considerable redundancy
e. Often considerable redundancy
f. Work locally rather than systemically.
C. Concept of autocrine vs. paracrine stimulation
II. Inflammatory Cytokines - Cytokines That Mediate Natural Immunity:
IL-1a,b Mf, Other T, Endot,, Brain Acute Phase Rx,
Fever, Costim.
TNFa,b Mf, T PMN, Endot. Brain, Multiple
Liver, T
IL-6 Multiple T, B, plasma cells, Multiple  esp
Liver Pl. Cell
IL-8 Multiple PMN chemotaxis
TypeI IFN Mf, Fib. All Antiviral, Inc.
a,b MHC I
A. IL-1 [(LAF - pyrogenic factor)]
1. Two forms ", ß only 20% homology but bind to same receptors
2. No signal peptide - initially produced an inactive pro-IL-1, which is
intracellular; cleaved by ICE (apoptosis enzyme  caspase 1); mechanism
of secretion unknown. ??Membrane IL-1.
3. Produced by many cell types - macrophages, epithelial cells, dendritic
B/T, astrocytes - major producer in the macrophages
4. Stimulus - irritant (UV light), T-MN interaction, other cytokines - TNF
5. Activities - involved in fever induction, acute phase response in liver,
many immunological functions are analogous to TNF; initially discovered
as being involved in T cell activation; ? induce production of high affinity
IL-2 receptors
B. Tumor Necrosis Factor [(TNFÄ…, ß); Lymphotoxin (TNFß)]
1. Two forms Ä…, ß - 30% homology - bind to same receptors
2. Long signal peptide segment (TNFÄ…) for MN released; TNFß is released
from activated T (esp. Tc) cells. Same question as IL-1 for mechanism of
TNFÄ… release but membrane form as a type II protein is confirmed. Is
trimeric.
3. Now obvious that a large family of cell-cell interaction molecules are
homologous with TNF and the receptors are also related: CD40/CD40L;
Fas/FasL; others with yet unknown function.
4. TNFÄ… - produced mainly by monocytes/macrophages some production by
lymphocytes. TNFß produced by T cells, may be in granules; released
along with granule contents
5. Stimulus - for MN - same as IL-1. For T cells activation of Tc causes
TNFß release.
6. Activities - Regression of some tumors - led to name TNF; other name is
cachexia "I have it bad" - wasting syndrome, septic shock, (Schwartzman
Reaction). Inflammation/granuloma formation.
III. IL-6 [B cell growth/differentiation factor, hepatocyte GF]
1. .20 Kd glycoprotein
2. Produced by monocytes, T cells, fibroblasts, endothelial cells
3. Function - promotes Ig production and B cell differentiation, promotes
continues growth/survival of plasma cells - (transgenics with elevated IL-6
die of myeloma) supports T cell growth along with IL-1 - Induces acute
phase proteins from hepatocytes
4. IL-11 shares many of IL-6 functions, including critical receptor
"triggering" chain (gp130)
B. IL-8 [NAP-1] MDNCF member of Ä…-chemokine-family
+
1. One of a growing number (20 ) of low mw "acute phase" proteins. IL-8 is
a 72 amino acid peptide/8 Kd mw that exists as a dimer. Charac. of """
family is that first two of four cys have a single a.a. interspersed, i.e.,
CXC.
2. Produced by monocytes/macrophages, fibroblasts epithelial cells
3. Stimulus - TNF/IL-1
4. Function - chemotaxis of PMN, and (to a lesser degree) T cells, basophils.
Activation of PMN.
5. Chemokine- family is related low mw, usually dimeric, first two of the
four cys have no interspersed a.a., i.e. CC. Prototypic example is MIP-"
a. Primarily chemotactic for monocytes/macrophages
b. Implicated recently as  suppressive agent for HIV
A. Type I interferon
1. 18-20 Kd proteins made by a variety of cells esp in response to viral inf.
2. Two forms; Interferon " (leukocyte-IFN) and ß (fibroblast-IFN), forms
show little homology but bind to same receptors. IFN-Å‚ is a further
division of IFN-Å‚.
3 Most potent signal for type I IFN induction is viral infection and is
experimentally induced with double stranded RNA
4. Biologic activities
a. Inhibits viral replication--paracrine like manner
b. Inhibits cell proliferation
c. Increases lytic potential of NK cells
d. Modulates (increases) MHC class I expression
III. Hematopoietic Growth Factors for Early Stem Cells, i.e. Relatively Multispecific
Factors. Source is usually stromal cells.
IL-3 Hem growth factor  esp. mast cells in mouse
GM-CSF Granulocyte, PMN, Mf stim. Promising for
neutropenia
G-CSF Granulocytes - PMNs
IL-7 Lymphocytes
SCF Ligand for c-kit  hematopoiesis  stem cell??
M-CSF Monocyte/macrophage
A. IL-3 [multi-CSF (colony stimulating factor)] -- hematopoietin fam. member
1. 0-30 Kd glycoprotein mouse/human only 20% homology and do not .
crossreact..
2. Produced by T cells, mast cells, epithelial cells
3. Stimulus - T cell or mast cell activation/normal production
4. Function - hematopoietic growth factor - formation of mast cells (esp.
mouse) macrophages, neutrophils, basophils, megakaryocytes
B. Colony Stimulating Factors [GM-CSF; Granulocyte-Macrophage stimulating
factor] --hem. fam. member.
1. 35 Kd glycoprotein
2. Produced by T cells, monocytes, macrophages, endothelial cells,
fibroblasts
3. Stimulus - activation/normal production
4. Function - granulocyte, neutrophil, macrophage stimulation; initial clinical
trials promising esp for neutropenia.
C. Granulocyte CSF -- hem. fam. member.
1. Stimulate committed progenitor to induce differentiation to granulocytes.
2. Clinical trials indicate promise for both granulocytes and neutrophils
D. IL-7 -- hem. fam. member.
1. pre-B, pre-T differentiation
E. Stem Cell Factor (SCF) -- ligand for c-kit -- rec. tyr-kinase family
1. 20 Kd protein (reported Oct. 1990)
2. Source - stromal cells - (generic name)
3. Function - hematopoiesis - perhaps of the pluripotent stem cell, mast cell
growth factor/non functional mutation is lethal
F. M-CSF (CSF-1) -- receptor for M-CSF is rec-tyr-kinase family member
1. Monocyte/macrophage colony formation
IV. Hematopoietic Growth/Differentiation and Cell Activation Factors - Lineage
Specific -- except for TGF² --are members of hem. family or IFN family.
A. IL-2 [T cell growth factor (TCGF)]
2. Source - T cells
3. Stimulus - IL-1/IL-6 T cell stimulation
4. Function - autocrine/paracrine growth and differentiation of T cells - NK
growth - B cell differentiation
5. Knockout mice indicate redundancy of cytokine system.
B. IL-4 [B cell growth factor]
1. 15 Kd glycoprotein producing by T cells and mast cells
2. Stimulus - cell activation
3. Function - promotes both T cell, mast cell, and (especially) B cell
growth/differentiation. Absolute requirement for IL-4 to see mouse IgE
production and essential for IgG production, i.e. isotype switch factor
4. Knockout mice show redundancy with IL-2 -- but have no IgE
C. IL-5 [T cell replacing factor; eosinophil DF]
1. 14 Kd glycoprotein product of T cells/mast cells
2. Stimulus - cell activation
3. Function - B cell differentiation, especially of IgA producing B cells;
growth/differentiation of eosinophils. Transgenics have very high
eosinophil levels -- effect on eos most imp in man.
D. Å‚-interferon [(Å‚-IFN), immune interferon]
1. 15 kd protein produced by T cells
2. Stimulus - cell activation
3. Function - very important in cellular immunity for activation of
macrophages; cells then acquire ability to kill intracellular organisms;
enhances some IgG production; inhibits Th2 growth
E. IL-10
1. 18-21 Kd protein expressed by a variety of cell types -- most imp.
probably Th2 cells
2. Highly related and biol. active protein encoded by Epstein Barr Virus.
3. Impairs accessory cell function by macrophages and NK cells -- net result
is inhibition of Th1 activity. Immunostimulatory to B cells and mast cells.
F. IL-12, 23, 27
1. Intriguing two chain cytokine molecules 70 - one chain has homology
with hem. and other with hem. receptors
2. Made by macrophages and dendritic cells.
3. Greatly augments (-IFN production and Th1 activity (CMI) -- as little as
1 µg of IL-12 can mediate a systemic effect such as turning off a Th2
response in a mouse.
G. IL-13, 15
1. Quite homologous in structure and function to IL-4 or IL-2 respectively
H. IL-17 Produced by T cells  induces inflammation by causing chemokine
production by fibroblasts, endothelial cells  important for anti-bacterial
immunity but also involved is some autoimmune diseases.
I. Other
1. Transforming growth factor ß (TGFß) - lymphocyte growth regulation
2. IL-9 --T cell source; costimulation of T and mast cells?
+
V. T Cell Cytokine Profile Differences [Th1 vs. Th2] (Both are CD4 T cells)
A. Th1 - favors cellular immunity - while Th2 favors humoral immunity.
Immune system must balance the two to have favorable situation
depending upon pathogen.
B. Lymphokine profile
New class  not Th1 or Th2  called Th-17 because of IL-17 production  seen when
IFNg and IL-4 are blocked and IL-23 is present.
C. How do Th1 and Th2 develop -- probably through intermediate Th0 -- then
depending upon environment -- Th1 or Th2 producing cell will develop.
1. Transcription factors that give selectivity  GATA3 (Th2) and T-bet (Th1)
 the latter is important esp. for IFNÅ‚ (production  and Th1 development
D. Course of disease state can be very different depending upon whether Th1 or Th2
predominate.
1. Leishmania example
2. Trichuris muris example
3. Leprosy example
E. Involvement of innate immunity in initial triggering
1. Type I pathogen  toll receptor interaction (dendritic cells/macs) gives IL-
12, IL-18 NK activation gives IFNÅ‚
VI. Cytokine synergy and pluripotency
A. In vivo - biological outcome is result of synergy/additive effect of
cytokines; many act in a variety of places
B. Most cytokines act on a variety of cell types  they are pluripotent.