Cytokines Messenger Molecules of the Immune System

Slide 1 · Cytokines: Messenger Molecules

of the Immune System

How soluble signals organize immunity, inflammation, and hematopoiesis

Innate initiation

Adaptive specialization

Immune regulation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What makes a cytokine a messenger?

Secreted proteins transmit information between immune and other host cells.

Cytokines regulate the magnitude, quality, and duration of inflammatory and immune responses.

The effect depends on the producing cell, responsive cell, and biological context.

Producer

Secreted cytokine

Receptor-bearing cell

Functional response

Slide 3 · The immune response is a cellular conversation

Lymphocytes, dendritic cells, macrophages, neutrophils, and endothelial cells interact.

Direct cell–cell recognition and soluble cytokine signaling are complementary mechanisms.

Cytokines allow one activated cell to change the behavior of many neighboring cells.

Cell–cell contact

Soluble cytokines

Compare the biological roles

Slide 4 · Cytokines are proteins, not a single pathway

Multiple molecularly distinct proteins share the functional label “cytokines.”

Effects include leukocyte activation, migration, proliferation, differentiation, and regulation.

No single cytokine explains the complete inflammatory response.

Cytokines

Activation

Migration

Differentiation

Slide 5 · Interleukin is a historical functional name

Interleukins were named for communication among leukocytes.

Many interleukins act on endothelial, epithelial, stromal, and other nonleukocyte cells.

“Interleukin” does not imply either a single cellular source or a leukocyte-only target.

Named by early function

Actual cellular scope

Compare the biological roles

Slide 6 · Cytokine production is widely distributed

Macrophages and dendritic cells are major early sources during innate responses.

Activated lymphocytes produce cytokines that direct adaptive effector functions.

Endothelial, epithelial, stromal, and additional inflammatory cells can also contribute.

Immune cells

Barrier cells

Stromal / vascular cells

Slide 7 · The target cell determines the effect

A secreted cytokine acts only on cells capable of responding to its signal.

Different target-cell programs can produce different outcomes to the same cytokine.

Cytokine identity alone does not fully specify the tissue response.

Cytokine release

Responsive target

Cell program

Tissue consequence

Slide 8 · Autocrine signaling reinforces activation

An activated cell can respond to a cytokine that it releases.

IL-2 secreted by activated T cells is a key example.

Autocrine signaling provides a mechanism for amplifying antigen-driven clonal expansion.

Activated T cell

IL-2 secretion

IL-2 receptor signaling

Schematic: Signaling reinforces the response

Slide 9 · Paracrine signaling organizes local responses

Cytokines act on adjacent leukocytes, endothelium, and stromal cells.

Local signaling coordinates recruitment and activation at the inflamed site.

The dominant inflammatory cytokine effects are often tissue-localized.

Activated leukocyte

Local cytokine

Endothelium / leukocytes

Local inflammation

Slide 10 · Endocrine signaling produces systemic effects

Some cytokines reach distant tissues or act systemically.

IL-1, TNF, and IL-6 contribute to fever and acute-phase responses.

Systemic activity can be protective or pathologic depending on intensity and duration.

Local infection

TNF / IL-1 / IL-6

Distant organs

Fever / acute phase

Slide 11 · Autocrine, paracrine, endocrine: Compare

Autocrine: The producer itself is the responder.

Paracrine: A nearby cell is the responder.

Endocrine: A distant tissue responds through systemic exposure.

Same cell

Neighboring cell

Distant tissue

Slide 12 · One cytokine may have several effects

Cytokines commonly act on multiple responsive cell populations.

TNF and IL-1 activate vascular endothelium and also contribute to systemic inflammation.

This broad activity explains why blocking one cytokine may influence several tissue functions.

TNF / IL-1

Endothelium

Leukocytes

Systemic tissues

Slide 13 · Cytokine effects overlap

TNF and IL-1 share important endothelial-activating actions.

Different cytokines can contribute to related processes such as neutrophil recruitment.

Overlapping actions make cytokine networks robust but can complicate therapy.

TNF → endothelium

IL-1 → endothelium

Compare the biological roles

Slide 14 · Sources and targets form a network

An individual cytokine may be released by several cell types.

One producer can release multiple mediators in response to a stimulus.

Tissue phenotype reflects coordinated signaling rather than an isolated protein.

Tissue response

Macrophage signals

Lymphocyte signals

Stromal signals

Slide 15 · Three functional domains of cytokines

Innate-response cytokines rapidly initiate defense and inflammation.

Adaptive-response cytokines drive lymphocyte expansion and specialized effector function.

Hematopoietic cytokines replenish leukocytes consumed during immune responses.

Innate defense

Adaptive effectors

Hematopoiesis

Slide 16 · Innate cytokines appear early

Microbial products and tissue injury activate innate immune cells.

Secreted mediators initiate leukocyte recruitment and antiviral defense.

They prepare the tissue environment in which adaptive immunity develops.

Microbe / injury

Innate sensing

Cytokine release

Initial defense

Slide 17 · Innate cytokine sources are diverse

Activated macrophages and dendritic cells are principal producers.

Innate lymphoid and natural killer cells also contribute.

Barrier, endothelial, and stromal cells add signals in the relevant tissue.

Macrophages / DCs

ILCs / NK cells

Barrier / stromal cells

Slide 18 · Key innate cytokine families

TNF and IL-1 support inflammatory cell recruitment.

Type I interferons establish antiviral responses.

IL-12 and IFN-γ connect innate activation with cell-mediated defenses; Chemokines guide cell migration.

TNF / IL-1

Type I IFNs

IL-12 / IFN-γ / chemokines

Slide 19 · TNF and IL-1: Shared inflammatory roles

Both are produced during responses to microbes, damage, and other inflammatory stimuli.

Both activate endothelium to support leukocyte adhesion and entry into tissues.

Both contribute to systemic manifestations of inflammation.

Inflammatory trigger

TNF + IL-1

Endothelial activation

Leukocyte entry

Slide 20 · What induces TNF and IL-1?

Microbial products, dead cells, immune complexes, foreign bodies, and physical injury can initiate release.

Microbial recognition receptors induce TNF production.

IL-1 synthesis also requires activation; Maturation of active IL-1 involves the inflammasome.

Microbes / damage

Innate sensors

TNF / IL-1 pathways

Inflammation

Slide 21 · Endothelial activation enables recruitment

TNF and IL-1 increase expression of endothelial adhesion molecules.

The stimulated endothelium also produces chemokines and other inflammatory mediators.

These changes help circulating leukocytes attach and enter tissues.

TNF / IL-1

Adhesion molecules

Leukocyte arrest

Transmigration

Slide 22 · Endothelial response extends beyond adhesion

TNF and IL-1 induce endothelial secretion of mediators and growth factors.

They also increase endothelial procoagulant activity.

The same signal therefore links inflammation to vascular and hemostatic changes.

Cell adhesion

Mediator release

Procoagulant state

Slide 23 · TNF amplifies leukocyte antimicrobial activity

TNF enhances neutrophil responses to additional stimuli.

It promotes macrophage microbicidal activity.

Persistent or excessive TNF activity may also contribute to tissue injury and systemic illness.

TNF

Leukocyte activation

Microbicidal response

Inflammatory cost

Slide 24 · IL-1 has tissue-specific additional roles

IL-1 contributes prominently to cytokine-associated fever.

It stimulates fibroblast collagen synthesis and proliferation of some mesenchymal cells.

IL-1 can also enhance Th17-type inflammation.

Fever

Fibroblast activation

Th17 responses

Slide 25 · Inflammatory cytokines cause fever

IL-1 and TNF act as endogenous pyrogens.

They promote prostaglandin-dependent changes in thermoregulation.

Fever is a systemic response to an underlying immune or inflammatory trigger.

Infection / injury

IL-1 + TNF

Prostaglandin response

Fever

Slide 26 · IL-6 drives the acute-phase response

IL-6 is produced by macrophages and other cells during inflammation.

It stimulates hepatic synthesis of important acute-phase proteins.

CRP and fibrinogen therefore reflect inflammation but do not identify its cause.

Inflammatory cells

IL-6

Liver

CRP / fibrinogen

Slide 27 · Chemokines direct leukocyte trafficking

Chemokines are small cytokine-family proteins with chemotactic activity.

They coordinate movement of selected leukocyte populations.

Their functions include both inflammation and positioning of cells in normal lymphoid tissue.

Chemokine source

Chemokine cue

Responsive leukocyte

Directed migration

Slide 28 · Chemokine receptors translate positional cues

Chemokine receptors are seven-transmembrane G protein–coupled receptors.

Leukocytes often express more than one chemokine receptor.

Receptor expression contributes to which cell populations follow a chemokine cue.

Chemokine

GPCR on leukocyte

Migration signaling

Cell movement

Slide 29 · Four structural chemokine families

CXC, CC, C, and CX3C classes are defined by the pattern of conserved cysteines.

This classification describes molecular structure, not a strict one-to-one target cell assignment.

Members of a family may have overlapping actions.

CXC

CC

C

CX3C

Slide 30 · CXCL8 helps recruit neutrophils

CXCL8, historically IL-8, belongs to the CXC chemokine family.

Activated macrophages and endothelial cells are among its sources.

CXCL8 activates and attracts neutrophils at inflammatory sites.

Macrophage / endothelium

CXCL8

Neutrophil

Inflamed tissue

Slide 31 · CCL2 attracts monocytes

CCL2, also known as MCP-1, is a CC chemokine.

CC chemokines commonly recruit monocytes and other mononuclear leukocytes.

This chemokine axis contributes to inflammatory cell accumulation in tissues.

Inflamed tissue

CCL2

Monocytes

Inflammatory infiltrate

Slide 32 · Chemokines support arrest and migration

Endothelium presents chemokines to passing leukocytes.

Chemokines increase leukocyte integrin affinity, promoting attachment to endothelium.

They then guide chemotaxis through tissue toward the inflammatory stimulus.

Chemokine display

Integrin activation

Firm adhesion

Chemotaxis

Slide 33 · Homeostatic chemokines organize lymphoid tissue

Not all chemokines are induced by acute inflammation.

Constitutively produced chemokines organize spatially distinct T-cell and B-cell regions.

Normal immune architecture therefore depends on positional cytokine signals.

Inflammatory trafficking

Homeostatic positioning

Compare the biological roles

Slide 34 · Type I interferons inhibit virus replication

Type I interferons are rapidly produced in innate antiviral responses.

Their principal function is to generate an antiviral state in responsive cells.

This activity is distinct from IFN-γ-driven macrophage activation.

Type I IFNs: Antiviral

IFN-γ: Macrophage activation

Compare the biological roles

Slide 35 · IL-12 connects sensing to cell-mediated defense

Macrophages and dendritic cells secrete IL-12 in relevant infections.

IL-12 promotes development of Th1 responses.

Th1 cells subsequently release IFN-γ to activate macrophages.

APC / IL-12

Th1 differentiation

IFN-γ

Macrophage activation

Slide 36 · IFN-γ activates macrophages

NK cells and T lymphocytes are important sources of IFN-γ.

IFN-γ increases macrophage capacity to kill ingested microbes.

Th1-derived IFN-γ cooperates with CD40-dependent signals for classical macrophage activation.

Th1 / NK cell

IFN-γ

Macrophage

Microbial killing

Slide 37 · Innate and adaptive signals reinforce one another

Innate macrophage and dendritic-cell signals shape the T-cell response.

Activated T cells send cytokine signals back to phagocytes.

This cooperation strengthens defense but may perpetuate chronic inflammation.

Innate APC cytokines

T-cell activation

Effector cytokines

Schematic: Signaling reinforces the response

Slide 38 · Antigen recognition is only the first step

T-cell activation requires recognition of antigen and costimulatory context.

Early helper T-cell cytokine production supports proliferation.

Differentiated effector T cells then deliver specialized cytokine programs.

Antigen + costimulation

T-cell activation

Cytokine secretion

Effector function

Slide 39 · CD4 T cells coordinate adaptive immunity

Activated CD4+ helper cells are major producers of adaptive cytokines.

Distinct helper subsets release different characteristic cytokines.

Their cytokine programs determine whether macrophages, eosinophils, neutrophils, or B cells are emphasized.

CD4+ T cells

Th1 pathway

Th2 pathway

Th17 pathway

Slide 40 · IL-2 supports clonal expansion

Activated CD4+ T cells produce IL-2 and upregulate high-affinity IL-2 receptors.

IL-2 then acts as an autocrine T-cell growth factor.

The result is expansion of antigen-specific lymphocytes.

Activated CD4+ cell

IL-2 release

High-affinity IL-2R

Schematic: Signaling reinforces the response

Slide 41 · IL-2 also supports CD8 responses

CD8+ T cells receive activating antigen and costimulatory signals.

Costimulation and IL-2 promote their proliferation.

The expanded cells differentiate into cytotoxic effector T lymphocytes.

Activated CD8+ cell

IL-2 + costimulation

Proliferation

Cytotoxic T cells

Slide 42 · Th1 immunity targets intracellular microbes

IL-12 promotes differentiation toward the Th1 subset.

Th1 cells produce IFN-γ, which strongly activates macrophages.

This program is important when pathogens survive within phagocytes.

IL-12

Th1 cell

IFN-γ

Classical macrophage activation

Slide 43 · Th2 immunity emphasizes barrier defense

Damaged epithelia release signals including IL-25, IL-33, and TSLP.

Th2 effector cells release IL-4, IL-5, and IL-13.

These cytokines support eosinophil responses and alternative macrophage activation.

Barrier stress

Th2-promoting signals

Th2 cytokines

Eosinophils / repair

Slide 44 · IL-5 links helper T cells to eosinophils

Th2 cells produce IL-5.

IL-5 activates eosinophils involved in defense against helminths.

A similar cytokine program may contribute to allergic inflammation.

Th2 cell

IL-5

Eosinophil

Helminth defense

Slide 45 · IL-4 and IL-13 reshape tissue responses

Th2-derived IL-4 and IL-13 induce alternative macrophage activation.

This macrophage program is associated with tissue repair and fibrosis.

The same cytokine environment is associated with IgE-mediated immunity.

Alternative activation

Repair / fibrosis

IgE-related responses

Slide 46 · Th17 immunity recruits phagocytes

Th17 cells produce IL-17 as a signature effector cytokine.

IL-17 induces chemokines that recruit neutrophils and monocytes.

This response is prominent in defense against extracellular bacteria and fungi.

Th17 cell

IL-17

Chemokines

Neutrophil recruitment

Slide 47 · IL-17 links lymphocytes to acute inflammation

A lymphocyte-derived cytokine can provoke a neutrophil-rich tissue response.

IL-17 acts in part by stimulating chemokine production by other cells.

Thus, adaptive immunity can amplify the cellular pattern typical of acute inflammation.

Activated T cell

IL-17

Tissue chemokines

Neutrophil influx

Slide 48 · Helper programs are functionally distinct

Th1: IFN-γ–dominated macrophage activation.

Th2: IL-4, IL-5, and IL-13–associated eosinophilic and repair responses.

Th17: IL-17–dependent recruitment of neutrophils and monocytes.

Th1 → macrophages

Th2 → eosinophils

Th17 → neutrophils

Slide 49 · Early tissue cues shape helper-cell fate

Intracellular infection favors IL-12 and a Th1-type response.

Barrier epithelial stress provides signals promoting Th2 immunity.

Fungal and some bacterial stimuli induce cytokine environments favoring Th17 responses.

IL-12 / Th1

Epithelial cues / Th2

Innate cues / Th17

Slide 50 · Cytokines cooperate with contact-dependent help

T helper cells also express CD40 ligand when engaging macrophages or B cells.

CD40 signaling and cytokines work together to activate the responding cell.

Cytokines should not be represented as replacing antigen recognition or cell contact.

CD40L–CD40 contact

Soluble cytokine signal

Compare the biological roles

Slide 51 · Tfh-cell help improves antibody responses

T follicular helper cells reside in lymphoid follicles with B cells.

Their helper signals include cytokines as well as CD40 ligand.

T-dependent responses undergo class switching and affinity maturation.

Tfh and B cell

CD40L + cytokines

Germinal center response

Improved antibodies

Slide 52 · Regulatory cytokines restrain responses

IL-10 and TGF-β are prominent cytokines that limit immune reactions.

Immune responses require active downregulation after their protective purpose is served.

Unchecked effector signals can sustain tissue-damaging inflammation.

Effector cytokines

IL-10 / TGF-β restraint

Compare the biological roles

Slide 53 · Effective immunity needs both accelerator and brake

Inflammatory cytokines help eliminate pathogens.

Regulatory cytokines prevent excessive or persistent responses.

The clinical outcome depends on the balance between host defense and collateral injury.

Host-defense signals

Regulatory signals

Compare the biological roles

Slide 54 · CSFs connect inflammation to bone marrow

Some cytokines stimulate growth of hematopoietic precursors.

They increase leukocyte production during immune and inflammatory responses.

This replenishes cells consumed or lost during inflammatory defense.

Inflammatory demand

Hematopoietic cytokines

Bone marrow progenitors

New leukocytes

Slide 55 · G-CSF supports granulocyte production

G-CSF is a colony-stimulating factor involved in leukocyte production.

It promotes expansion of the granulocytic compartment.

Clinically administered G-CSF is used to support neutrophil recovery in selected settings.

G-CSF

Marrow progenitors

Granulocyte production

Neutrophil recovery

Slide 56 · GM-CSF supports hematopoiesis

GM-CSF is a cytokine with colony-stimulating activity.

Macrophages, T cells, and marrow stromal cells are among relevant sources of hematopoietic cytokines.

Therapeutic administration can enhance cytokine-dependent blood-cell production.

GM-CSF

Bone marrow

Myeloid-cell production

Replenished defense

Slide 57 · IL-3 belongs to the hematopoietic group

IL-3 is listed among colony-stimulating cytokines.

These factors support increased blood-cell production when leukocyte demand rises.

Their role differs from TNF/IL-1-mediated endothelial activation.

IL-3: Marrow support

TNF/IL-1: Inflammation

Compare the biological roles

Slide 58 · Cytokines scale leukocyte supply to demand

Inflammation both recruits cells into tissues and consumes short-lived leukocytes.

CSFs increase marrow output to replenish the peripheral pool.

Defense therefore depends on recruitment signals and production signals working together.

Inflammatory cell loss

CSF signal

Marrow response

Restored leukocyte pool

Slide 59 · Chronic inflammation can become self-sustaining

Macrophages and activated lymphocytes reciprocally stimulate one another.

Their cytokines drive recruitment, activation, and tissue injury.

Persistent stimuli can maintain this network long after the initial response.

Macrophage cytokines

T-cell activation

T-cell cytokines

Schematic: Signaling reinforces the response

Slide 60 · Systemic cytokines have costs

TNF, IL-1, and IL-6 induce physiological acute-phase responses.

Persistent excessive inflammatory signaling can produce illness and tissue damage.

Mechanisms beneficial in short host defense may be harmful when prolonged.

Local defense

Systemic response

Pathologic persistence

Slide 61 · Anti-TNF treatment validates cytokine targeting

TNF contributes to tissue-damaging chronic inflammatory diseases.

TNF antagonists can yield substantial clinical responses in rheumatoid arthritis.

Treatment demonstrates that cytokine blockade can interrupt a disease-driving mechanism.

TNF-dependent inflammation

TNF inhibition

Reduced inflammation

Clinical benefit

Slide 62 · Anti-cytokine therapies target distinct axes

The Robbins inflammation chapter describes IL-6-receptor antagonism in juvenile arthritis.

It also describes IL-17 antagonism in psoriasis.

The target should match the disease-relevant inflammatory pathway.

IL-6R inhibition

IL-17 inhibition

Compare the biological roles

Slide 63 · Cytokine blockade has host-defense tradeoffs

TNF contributes to macrophage-mediated protection from intracellular infection.

TNF inhibition can increase susceptibility to mycobacterial infection.

Immune-directed therapy requires mechanistic risk assessment, not efficacy alone.

TNF blockade

Reduced inflammation

Reduced defense

Infection risk

Slide 64 · Cytokines can also be administered therapeutically

Blocking cytokine action reduces an excessive response.

Administering selected cytokines supports functions dependent on those proteins.

Hematopoietic support with erythropoietin and GM-CSF as examples.

Block: Inflammation

Provide: Hematopoiesis

Compare the biological roles

Slide 65 · Case: Febrile infection with high CRP

A microbial trigger activates macrophages and related innate cells.

IL-1 and TNF contribute to fever; IL-6 promotes the hepatic acute-phase response.

Interpret CRP as evidence of inflammation, not proof of a specific organism.

Microbial stimulus

IL-1 / TNF + IL-6

Fever + liver response

Clinical findings

Slide 66 · Case: Neutrophil-rich tissue inflammation

An inflammatory signal induces chemokines at the affected site.

CXCL8 recruits neutrophils; IL-17 can amplify neutrophil recruitment indirectly.

Cellular recruitment follows communication between resident cells, endothelium, and leukocytes.

Inflamed tissue

Chemokines / IL-17

Neutrophils

Inflammatory infiltrate

Slide 67 · Case: Intracellular pathogen persistence

Dendritic cells and macrophages can release IL-12.

Th1-associated IFN-γ activates macrophages to improve intracellular killing.

Interrupting this axis can impair host defense even if inflammation is reduced.

IL-12

Th1 / IFN-γ

Activated macrophage

Intracellular defense

Slide 68 · Case: Chronic inflammatory synovitis

Persistent macrophage–T-cell signaling can sustain tissue inflammation.

TNF is a targetable mediator in rheumatoid arthritis.

Clinical benefit from blockade does not imply cytokines are dispensable for host defense.

Immune activation

TNF-dependent injury

TNF antagonist

Inflammation reduced

Slide 69 · Integrating cytokines into a tissue response

Innate cells initiate inflammation and activate endothelium.

Adaptive subsets tailor the effector response to the microbial challenge.

Regulatory cytokines limit activity while colony-stimulating factors replenish leukocytes.

Initiation

Effector choice

Restraint

Replenishment

Slide 70 · Six cytokine relationships worth retaining

TNF/IL-1 → endothelial activation; IL-6 → acute-phase proteins.

CXCL8 → neutrophil recruitment; IL-12 → Th1 differentiation.

IL-2 → T-cell expansion; IFN-γ → macrophage activation.

CYTOKINE

MAJOR FUNCTION

TNF / IL-1

Endothelial activation

IL-6

Acute-phase response

CXCL8

Neutrophil recruitment

IL-2 / IFN-γ

T-cell expansion / macrophages

Slide 71 · The cytokine system is an integrated network

Cytokines connect immune sensing to cell recruitment and effector specialization.

Their actions vary with source, target, and whether signaling is local or systemic.

Targeted manipulation is valuable precisely because these pathways drive both protection and pathology.

Sensing

Coordination

Outcome

Slide 72 · Textbook basis and source boundaries

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026)

Chapter 6: cytokines as immune messengers; lymphocyte activation and helper subsets.

Chapter 3: TNF, IL-1, IL-6, chemokines, inflammation, and systemic effects.

Related hematopoietic context: colony-stimulating factors.

All teaching schematics are original, editable PowerPoint shapes; no textbook figures were reproduced.