Cytopathic Cytoproliferative Reaction

Slide 1 · Cytopathic–cytoproliferative reaction

Cellular patterns of virus-associated tissue injury and proliferation

Infectious-disease morphology · mechanisms and clinicopathologic interpretation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Recognize cytopathic and cytoproliferative reaction patterns as morphologic responses to infection.

Explain inclusions, cell fusion, epithelial vesiculation, and proliferation from their mechanisms.

Apply the pattern to HSV, VZV, measles, CMV, HPV, molluscum, and EBV.

Distinguish direct viral cytopathology from immune-mediated injury and neoplastic transformation.

Slide 3 · The pattern is a tissue reaction, not one disease

Virus infects susceptible cells

Direct cellular alteration

Characteristic tissue pattern

Several viruses produce overlapping patterns; Morphology narrows, but does not uniquely name, the agent.

Slide 4 · Position within the spectrum of infection

Suppurative

Prominent neutrophilic exudate

Pus / microabscess formation

Cytopathic–proliferative

Altered infected cells; Often few inflammatory cells

Necrosis, fusion, or proliferation

Chronic/scarring

Prolonged inflammation and tissue remodeling

Loss of normal architecture

Slide 5 · Three complementary outcomes of infected cells

Cytolytic injury

Cell–cell fusion

Epithelial or lymphoid proliferation

A single virus can generate more than one of these outcomes, depending on the infected cell and host context.

Slide 6 · Cytopathic versus cytoproliferative

Cytopathic

Cell enlargement, inclusions, necrosis

Vesicles or lytic epithelial damage

Cytoproliferative

Increased number or expansion of affected cells

Warts, papules, lymphoid proliferation

Slide 7 · Morphology begins with the affected cell

Look first for altered nuclei, cytoplasm, and cell boundaries.

Then determine whether affected cells die, fuse, or expand.

Finally assess associated inflammation and the architecture of the lesion.

Slide 8 · Virus–host interaction determines injury

Viral entry and replication

Altered cell metabolism or survival

Cell loss, persistence, or proliferation

Viruses may directly injure host cells; Host immunity can cause additional damage.

Slide 9 · Tropism explains selective cellular injury

Host cell entry receptor / lineage factor

Viral access to a permissive cell

Characteristic cellular distribution

Tropism is the predilection of a virus for particular host cells, not a guarantee that all similarly shaped cells are infected.

Slide 10 · Tropism has molecular and cellular determinants

Host entry receptors as an important determinant of tropism.

EBV binds CD21 (CR2) on B cells; Other viruses use different receptors.

Cell lineage–specific factors can further restrict infection.

Slide 11 · Direct viral injury can dominate the image

Productive infection

Cellular structural damage

Cell death / necrosis

The core Robbins reaction may show conspicuous infected-cell alterations even when inflammatory cells are sparse.

Slide 12 · Direct and immune-mediated injury are distinct

Direct cytopathic damage

Virus replication alters the infected cell

HSV epithelial cytolysis

Host immune injury

Effector cells attack infected tissues

Inflammatory damage in viral hepatitis or HSV stromal keratitis

Slide 13 · Sparse inflammation is a pattern, not a rule

Inflammatory cells as “usually” sparse in cytopathic–cytoproliferative lesions.

Inflammation depends on timing, tissue site, pathogen, and immune competence.

Concurrent inflammatory or necrotizing reaction patterns can coexist.

Slide 14 · Viral inclusions provide a cytologic clue

Nuclear inclusion

Schematic · not a histologic specimen

A visible aggregate or viral-associated alteration may appear within an infected cell.

Robbins specifically cites herpesviruses and adenovirus as inclusion-forming examples.

Slide 15 · Nuclear and cytoplasmic locations matter

Nuclear

HSV, VZV, CMV and adenovirus are examples with nuclear inclusions.

Assess chromatin and nuclear architecture.

Cytoplasmic

Molluscum produces intracytoplasmic viral inclusions.

Assess the cytoplasmic compartment.

Slide 16 · An inclusion is a clue, not a full diagnosis

Morphologic inclusions must be interpreted alongside tissue distribution and clinical setting.

Different viruses can produce nuclear inclusion-like changes.

Inclusions may be absent in some infected cells or lesions.

Slide 17 · Cell fusion creates multinucleated polykaryons

Shared cytoplasm

Multiple nuclei

Schematic · not a histologic specimen

Virus-induced fusion preserves several nuclei within a shared cell boundary.

Robbins gives measles virus and herpesviruses as examples.

Slide 18 · Polykaryon is not synonymous with granuloma

Virus-associated polykaryon

Fusion of infected cells

Correlate with epithelial or lymphoid infection

Granulomatous giant cell

Aggregation and fusion of activated macrophages

Correlate with epithelioid histiocytes / granuloma

Slide 19 · Focal epithelial injury can form a blister

Intraepithelial cleft

Epithelial layer

Schematic · not a histologic specimen

Injured epithelial cells lose cohesion or detach.

A fluid-containing cleft develops within the epithelial layer.

The result is a vesicular lesion rather than a proliferative papule.

Slide 20 · Cytopathic damage can progress to ulceration

Ballooning epithelial injury

Vesicle / blister

Rupture and superficial ulceration

This sequence is described in the Robbins morphology of herpes simplex lesions.

Slide 21 · Four morphologic signs to recognize

Inclusion

Altered nuclear or cytoplasmic material

Cell-level

Multinucleation

Several nuclei in fused cytoplasm

Cell-level

Vesicle

Cleft from epithelial destruction

Tissue-level

Papillomatous growth

Expanded epithelium / papules

Tissue-level

Slide 22 · HSV: Epithelial infection and cytolysis

HSV infects skin / mucosa

Viral replication in epithelium

Vesicular lesion

HSV-1 and HSV-2 produce similar cytopathic patterns, despite differing clinical distributions.

Slide 23 · HSV: Intranuclear Cowdry type A inclusions

Nuclear inclusion

Schematic · not a histologic specimen

Large pink-to-purple intranuclear inclusions appear in infected epithelial cells.

Peripheral displacement of host chromatin accompanies inclusion formation.

Slide 24 · HSV: Viral-induced multinucleated syncytia

Shared cytoplasm

Multiple nuclei

Schematic · not a histologic specimen

Fusion produces multinucleated epithelial cells.

The same lesion can show both nuclear inclusions and syncytial cells.

Slide 25 · HSV: Ballooning degeneration and vesicles

Intraepithelial cleft

Epithelial layer

Schematic · not a histologic specimen

Intracellular edema and ballooning degeneration disrupt epithelial integrity.

Intraepithelial vesicles may burst, crust, or create superficial erosions.

Slide 26 · HSV latency changes the site of persistence

Primary mucocutaneous infection

Transport to sensory ganglion

Latent viral genome in neurons

Visible cytopathic damage characterizes epithelial replication, not necessarily neuronal latency.

Slide 27 · HSV reactivation reconnects ganglion and skin

Neuronal viral reactivation

Axonal spread outward

Recurrent skin / mucosal lesion

A recurrent vesicular eruption reflects viral return to the peripheral site of infection.

Slide 28 · HSV corneal disease: Two injury mechanisms

Epithelial keratitis

Virus-induced epithelial cytolysis

Direct cytopathic injury

Stromal keratitis

Mononuclear infiltrates, neovascularization and scarring

Immune-mediated tissue damage

Slide 29 · VZV primary infection creates widespread vesicles

Primary varicella infection

Disseminated cutaneous eruption

Intraepithelial vesicles

Chickenpox lesions that evolve from macules to vesicles and then crusts.

Slide 30 · VZV reactivation produces dermatomal shingles

Latent VZV in sensory ganglion

Reactivation and sensory-nerve spread

Dermatomal vesicles, often painful

The epithelial cytopathic effect coexists with radiculoneuritis-related pain.

Slide 31 · VZV histology links inclusion and vesicle

Intraepithelial cleft

Epithelial layer

Schematic · not a histologic specimen

Chickenpox lesions show intraepithelial vesicles.

Intranuclear inclusions occur in cells at the vesicle base.

Rupture may be followed by crusting and regeneration.

Slide 32 · HSV and VZV share a cell-injury pattern

Shared morphology

Vesicular epithelial injury; Intranuclear inclusions

Histology alone may not settle viral type

Clinical context differs

HSV mucocutaneous recurrences; VZV varicella or dermatomal zoster

Distribution helps focus etiologic testing

Slide 33 · Measles is a prototype of virus-induced fusion

Measles viral fusion activity

Fusion of neighboring host cells

Multinucleate giant cells

Cell fusion to the measles fusion (F) protein.

Slide 34 · Warthin–Finkeldey cells in measles

Shared cytoplasm

Multiple nuclei

Schematic · not a histologic specimen

Multinucleated giant cells can be distributed in lymphoid organs.

Eosinophilic nuclear and cytoplasmic inclusions.

Slide 35 · Measles rash also has immune morphology

Vascular dilation, edema, and mononuclear perivascular cells accompany the rash.

T-cell-mediated immunity helps control measles and contributes to the cutaneous eruption.

Thus, a virus with a syncytial cytopathic signature can also produce a conspicuous host reaction.

Slide 36 · Adenovirus is a nuclear-inclusion example

Nuclear inclusion

Schematic · not a histologic specimen

The cytopathic–cytoproliferative heading explicitly includes adenovirus among inclusion-forming viruses.

This fact identifies a morphologic category; It does not establish adenovirus from inclusions alone.

Slide 37 · CMV characteristically enlarges infected cells

Uninfected cell

Enlarged infected cell

Schematic · not a histologic specimen

CMV-infected cells may show marked enlargement of the whole cell and nucleus.

The name “cytomegalovirus” reflects this distinctive cellular enlargement.

Slide 38 · CMV: Large inclusion with a clear halo

Intranuclear inclusion

And surrounding halo

Schematic · not a histologic specimen

A prominent intranuclear basophilic inclusion is separated from the nuclear envelope by a clear halo.

This is conventionally described as the “owl’s eye” appearance.

Slide 39 · CMV disease depends strongly on immune status

Preserved immunity

Often asymptomatic or mononucleosis-like illness

Cellular injury may be clinically limited

Impaired cellular immunity

Reactivation and systemic tissue infection may occur

Greater clinical impact across organs

Slide 40 · Mixed infection may produce mixed tissue reactions

CMV in lung

Cytologic alterations of infected alveolar lining cells

Cytopathic morphology

Pneumocystis in lung

Interstitial inflammation

Distinct simultaneous reaction pattern

Slide 41 · Cytoproliferation means altered growth

Virus affects epithelial cell regulation

Local cell proliferation

Visible papillomatous or papular lesion

HPV-associated warts and poxvirus-associated molluscum papules as characteristic examples.

Slide 42 · HPV: Proliferating squamous epithelium forms warts

HPV infection of epithelium

Epidermal thickening / papillary growth

Verruca or condyloma

The macroscopic growth pattern reflects epithelial proliferation rather than simply inflammation.

Slide 43 · A wart has a papillomatous architecture

Papillomatous projections

Schematic · not a histologic specimen

Common warts show undulant or spire-like epidermal proliferation.

Papillomatous hyperplasia describes the architectural change.

Slide 44 · HPV: Koilocytosis is a cytopathic change

Perinuclear halo

Schematic · not a histologic specimen

Superficial squamous cells show perinuclear clearing (“halo”).

Associated nuclear enlargement and hyperchromasia make the cell abnormal.

Slide 45 · HPV combines proliferation and cytopathic injury

Architectural finding

Papillomatous epithelial expansion

Cytoproliferative component

Cellular finding

Koilocytotic perinuclear halo and nuclear atypia

Cytopathic component

Slide 46 · Condyloma and common wart: Shared biology

Verruca vulgaris

Rough hyperkeratotic / papillomatous cutaneous lesion

Koilocytosis can be conspicuous

Condyloma acuminatum

Soft anogenital cauliflower-like growth

Diagnosis draws on papillary architecture and koilocytosis

Slide 47 · Benign HPV proliferation differs from cancer

Low-risk types

HPV 6 and 11 commonly produce genital warts

Low malignant potential

High-risk types

HPV 16 and 18 are implicated in multiple squamous carcinomas

Cancer risk associated with persistent infection and molecular changes

Slide 48 · High-risk HPV shifts cell-cycle control

Persistent high-risk HPV

Expression of E6 and E7

Loss of tumor-suppressor restraint

Viral oncogenic action from the visible papillomatous growth of a benign wart.

Slide 49 · HPV E6 undermines p53 function

High-risk HPV E6

P53 degradation; Increased TERT expression

Reduced checkpoint restraint / senescence

E6 is a molecular mechanism of HPV-associated oncogenesis, not a histologic inclusion body.

Slide 50 · HPV E7 undermines RB function

High-risk HPV E7

RB binding; E2F release

Accelerated G1/S progression

Robbins also notes inhibition of p21 and p27 and modulation of cyclin activity.

Slide 51 · HPV infection alone does not ensure carcinoma

High-risk HPV is causally important, but progression usually requires additional genetic or epigenetic alterations.

The relevant distinction is productive benign epithelial growth versus transformed malignant growth.

A virus-associated proliferation is not automatically a cancer.

Slide 52 · Molluscum: Proliferative umbilicated papules

Central indentation

Epithelial proliferation

Schematic · not a histologic specimen

Poxvirus infection creates characteristic pearly dome-shaped papules with a depressed center.

The lesion is an epithelial proliferation with a recognizable clinical architecture.

Slide 53 · Molluscum: Inclusions are cytoplasmic

Cytoplasmic inclusion

Schematic · not a histologic specimen

The central core of a papule contains infected cells with intracytoplasmic viral inclusions.

Compartment location contrasts with the classic herpesvirus nuclear inclusion.

Slide 54 · HPV and molluscum: Two types of papules

HPV wart

Papillomatous / verruciform epithelial growth

Koilocytosis in upper layers

Molluscum contagiosum

Dome-shaped umbilicated papule

Cytoplasmic inclusions

Slide 55 · EBV produces a proliferative B-cell response

EBV entry into B cells

Latent viral proteins activate cells

B-cell proliferation

LMP1 and EBNA2 as proteins that promote infected B-cell activation and expansion.

Slide 56 · EBV mononucleosis is not just B-cell expansion

EBV-infected B cells

A proliferating, virally infected cell population

Latent viral proteins in a minority of nodal cells

Reactive T cells

Expanded antiviral CD8+ response

Atypical lymphocytes; Paracortical expansion

Slide 57 · EBV links benign lymphoproliferation and cancer

EBV causes a benign, often self-limited infectious mononucleosis syndrome.

It also contributes to the pathogenesis of some lymphomas and nasopharyngeal carcinoma.

A viral association does not mean every expanded lymphoid population is malignant.

Slide 58 · Reaction pattern by exemplar

Virus

Signature cytopathic / proliferative feature

HSV / VZV

Intranuclear inclusions; Epithelial vesicles; Fusion

Measles

Multinucleated giant cells / syncytia

CMV

Cytomegaly with prominent nuclear inclusion

HPV

Papillomatous proliferation and koilocytosis

Molluscum

Umbilicated papule; Cytoplasmic inclusions

EBV

Infected B-cell proliferation; Reactive lymphoid expansion

Slide 59 · Suppuration and cytopathic injury differ

Purulent reaction

Numerous neutrophils and pus

Classically prominent in pyogenic bacterial infections

Cytopathic reaction

Affected cells may dominate despite little inflammation

Classically viral inclusions, fusion or vesiculation

Slide 60 · Tissue necrosis can eclipse specific inclusions

Cytopathic pattern

Individual infected cells show inclusions, fusion or architectural effects

Cell-level clues may be preserved

Necrotizing pattern

Extensive destruction becomes the dominant feature

HSV brain or HBV liver cited as severe examples

Slide 61 · Mixed patterns challenge single-label diagnosis

Robbins cautions that host tissue responses rarely occur in pure form.

One lesion can combine cytopathic change, necrosis, and inflammation.

A mixed pattern can also reflect simultaneous infections, particularly in immunosuppressed hosts.

Slide 62 · Interpret the lesion in a fixed sequence

Identify cell-level alteration

Characterize tissue architecture

Integrate inflammation and clinical context

Choose targeted etiologic confirmation when morphology is compatible but nonspecific.

Slide 63 · Case: Painful recurrent grouped mucosal vesicles

A patient develops recurrent localized vesicles near the lip. Biopsy shows intraepithelial vesiculation and inclusion-bearing multinucleated epithelial cells.

What reaction pattern is demonstrated, and which virus is favored?

Interpretation: Cytopathic reaction with epithelial injury, syncytia, and nuclear inclusions; HSV is favored by the recurrent localized mucocutaneous setting.

Slide 64 · Case: Unilateral painful dermatomal eruption

A person develops painful vesicles restricted to one sensory dermatome. Infected keratinocytes contain intranuclear inclusions.

How do distribution and cellular findings complement one another?

Interpretation: Intranuclear inclusion–associated epithelial cytopathy indicates a viral reaction; The dermatomal, painful recurrence points toward VZV reactivation.

Slide 65 · Case: Papule with epithelial viral inclusions

A small, pearly umbilicated skin papule has an epithelial core of cells containing cytoplasmic inclusions.

Which pattern and etiologic group are suggested?

Interpretation: Cytoproliferative papule with intracytoplasmic inclusions, characteristic of molluscum contagiosum (poxvirus).

Slide 66 · Case: Papillary growth with koilocytosis

An anogenital exophytic lesion shows papillary epithelial hyperplasia and koilocytosis in superficial cells.

What mechanism explains the tissue architecture and nuclear/cytoplasmic change?

Interpretation: HPV-associated epithelial proliferation and cytopathic koilocytosis; Benign condyloma is favored by this combined pattern.

Slide 67 · Synthesis: Follow the cells, then the tissue

Inclusions and multinucleation indicate virus-associated alterations of infected cells.

Vesicles reflect epithelial injury; Papillomas and some papules reflect epithelial proliferation.

Specific viral examples must be interpreted in clinical and tissue context.

The reaction may coexist with inflammation, necrosis, or neoplastic transformation.

Slide 68 · Primary references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Ch. 8: Infectious Diseases, esp. pp. 308–325.

Related source sections: Ch. 7 (HPV / viral oncogenesis); Ch. 22 (molluscum in genital tract); Ch. 25 (viral skin lesions).

All diagrams in this lecture are original, editable schematics; no textbook figures or authentic photomicrographs were reproduced.