Infectious disease notes from a helpful teacher

Pathology of Infectious DiseasesPathology of Infectious Diseases

J Stephen Dumler M DJ Stephen Dumler M DJ. Stephen Dumler, M.D.J. Stephen Dumler, M.D.

host responsehost response vs. microbial pathogensvs. microbial pathogens

•• Important host response factorsImportant host response factorsintrinsic host defenses and innate immunityintrinsic host defenses and innate immunityadaptive immunity and immune competenceadaptive immunity and immune competencegenetic backgroundgenetic background

•• Important bacterial factorsImportant bacterial factorsroute of entryroute of entryability to gain access to hostability to gain access to hostsize of inoculum, ability to use host substratessize of inoculum, ability to use host substratesability to circumvent host responsesability to circumvent host responsesbacterial products that damage cells or tissues, or alter host bacterial products that damage cells or tissues, or alter host

physiologyphysiologyevolutionary adaptation to hostevolutionary adaptation to host

Respiratory tract entry Gastrointestinal tract entry

margination of leukocytesmargination of leukocytes

Time Course of InflammationTime Course of InflammationThe earliest cellular event in inflammation is an influx of neutrophils beginning after a few hours Monocytes andhours. Monocytes and macrophages characterize the later stages of inflammation. Eventually, fibroblasts may repair the site and endothelial cells provide new blood vessels.

Blood cells involved in inflammationNeutrophilsNeutrophils Basophils & Basophils &

Mast cellsMast cellsEosinophilsEosinophils

GranulocytesGranulocytes

Acute inflammationAcute inflammationAllergies and Allergies and

parasitic infectionsparasitic infectionsAllergic Allergic

hypersensitivityhypersensitivity

Mononuclear phagocytesMononuclear phagocytesmonocytes andmonocytes and macrophages (histiocytes)macrophages (histiocytes)

•• PhagocyticPhagocytic

•• Participates in Participates in induction of induction of immuneimmune

monocytemonocyte macrophagemacrophage

immune immune reactions reactions (antigen (antigen presentation)presentation)

•• Source of Source of proinflammatory proinflammatory cytokinescytokines

Lymphocytes and Plasma cells

• Not a frequent component of acute inflammation

• initiators and effectors of immune response

(• T lymphocytes (helper, cytotoxic, natural killer)

• B lymphocytes and plasma cells produce antibody

• Natural killer (NK) cells produce proinflammatory cytokines and lyse target cells

Lymphocyte Plasma cell

Inflammation definitions• Edema – accumulation of extrvascular fluid• Effusion – accumulation of fluid in a body cavity (e.g.

peritoneum or pleura)• Transudate – edema fluid with low protein content (s.g. <1.015)• Exudate – edema fluid with high protein content (s.g. >1.015),

often with inflammatory cells– Serous exudate – exudate lacking large number of inflammatory g g y

cells; usually pale yellow– Serosanguinous – exudate or effusion containing erythrocytes

(usually red-tinged)– Fibrinous exudate – contains large amount of fibrin after

coagulation of clotting factors– Purulent exudate or effusion – contains high inflammatory cell

content; often seen with bacterial infections– Suppurative inflammation – purulent exudate accompanied by

significant liquifactive necrosis (pus).

Edema and Edema and fibrinousfibrinous exudateexudate(bronchopneumonia)(bronchopneumonia)

FibrinousFibrinous pericarditispericarditis

Purulent exudateBronchopneumonia

Purulent exudate: Meningitis

Purulent and suppurative Purulent and suppurative inflammationinflammation

Purulent exudate (liver Purulent exudate (liver abscess)abscess)

Suppurative Myocardial Suppurative Myocardial InflammationInflammation

Ulcers

UlcerUlcer

UlcerUlcer

Gastric UlcerGastric Ulcer

ArteryArtery

PseudomembranousPseudomembranous InflammationInflammation

PseudomembranePseudomembrane

PseudomembranousPseudomembranous((Clostridium difficileClostridium difficile) colitis) colitis

Histopathology with bacterial infectionsHistopathology with bacterial infections

•• Extracellular bacteriaExtracellular bacteria–– Incite acute inflammation with edemaIncite acute inflammation with edema

•• exudativeexudative

–– Depending upon bacterial species, may cause necrosis Depending upon bacterial species, may cause necrosis suppuration (pus) or abscesssuppuration (pus) or abscess

•• exudativeexudative with necrosiswith necrosis•• abscessabscess

With ti i i h i i fl ti b i l diWith ti i i h i i fl ti b i l di–– With time, increasing chronic inflammation begins leading With time, increasing chronic inflammation begins leading various degrees of mixed acute and chronic inflammationvarious degrees of mixed acute and chronic inflammation

–– Examples:Examples:•• Streptococcus pneumoniaeStreptococcus pneumoniae•• Staphylococcus aureusStaphylococcus aureus•• Pseudomonas aeruginosaPseudomonas aeruginosa•• Most other bacteriaMost other bacteria

Exudative InflammationExudative Inflammation

•• vascular permeability, recruitment of vascular permeability, recruitment of leukocytes (esp. neutrophils), pusleukocytes (esp. neutrophils), pus

•• typically caused by pyogenic, extracellular typically caused by pyogenic, extracellular bacteriabacteria

•• usually localizedusually localized•• usually localized usually localized

•• examples:examples: group A strep (group A strep (Streptococcus pyogenesStreptococcus pyogenes) )

pharyngitispharyngitis

Staphylococcus aureus Staphylococcus aureus furunclefuruncle

Streptococcus pneumoniae Streptococcus pneumoniae pneumonia and pneumonia and meningitismeningitis

ExudativeInflammation

Streptococcal pharyngitis

(strep throat)

Lobar pneumonia Lobar pneumonia –– S. pneumoniaeS. pneumoniae

Lobar pneumonia Lobar pneumonia –– S. pneumoniaeS. pneumoniae Meningitis Meningitis –– Streptococcus pneumoniaeStreptococcus pneumoniae

Meningitis Meningitis –– Streptococcus pneumoniaeStreptococcus pneumoniae

Necrotizing InflammationNecrotizing Inflammation•• exudativeexudative inflammation with necrosis inflammation with necrosis

(suppuration)(suppuration)

•• host damage may be caused by host damage may be caused by bacterial virulence factorsbacterial virulence factors

•• examples:examples: Pseudomonas aeruginosa Pseudomonas aeruginosa pneumoniapneumonia

Clostridium perfringens Clostridium perfringens myonecrosismyonecrosis (gas (gas gangrene)gangrene)

Necrotizing pneumoniaNecrotizing pneumonia Necrotizing pneumonia Necrotizing pneumonia –– Pseudomonas aeruginosaPseudomonas aeruginosa

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Gram stainGram stain

Clostridium perfringensClostridium perfringens myonecrosis (gas gangrene)myonecrosis (gas gangrene)

Gram stainGram stain

Clostridium perfringensClostridium perfringens myonecrosis (gas gangrene)myonecrosis (gas gangrene)

Histopathology with bacterial infectionsHistopathology with bacterial infections

•• Facultative and obligate intracellular bacteriaFacultative and obligate intracellular bacteria–– Incite chronic inflammation Incite chronic inflammation acute inflammationacute inflammation

•• chronic inflammation or mixed acute and chronic inflammationchronic inflammation or mixed acute and chronic inflammation•• granulomas or granulomatous inflammationgranulomas or granulomatous inflammation

–– Depending upon bacterial species, may cause necrosis Depending upon bacterial species, may cause necrosis •• caseous necrosiscaseous necrosis•• microabcesses within granulomatous inflammationmicroabcesses within granulomatous inflammationgg•• host cellhost cell--specific necrosis or apoptosisspecific necrosis or apoptosis

–– Examples:Examples:•• Mycobacterium tuberculosis Mycobacterium tuberculosis (tuberculosis)(tuberculosis)•• Rickettsia rickettsii Rickettsia rickettsii (Rocky Mountain spotted fever)(Rocky Mountain spotted fever)•• Mycoplasma pneumoniae Mycoplasma pneumoniae pneumonitispneumonitis•• Chlamydia trachomatisChlamydia trachomatis ((lymphogranulomalymphogranuloma venereumvenereum and and

urogenital infections)urogenital infections)

Granulomatous Inflammation and Granulomatous Inflammation and GranulomasGranulomas

•• accumulations of accumulations of epithelioidepithelioidhistiocytes (activated macrophages)histiocytes (activated macrophages)

•• response to bacteria that withstand response to bacteria that withstand destruction by neutrophil phagocytesdestruction by neutrophil phagocytes

•• dependent upon intact, appropriate dependent upon intact, appropriate p p , pp pp p , pp pcytokine responses (ILcytokine responses (IL--11, IFN, IFN--, , CXCL and CCL chemokines, not ILCXCL and CCL chemokines, not IL--4 4 or ILor IL--10)10)

•• examples:examples: Mycobacterium tuberculosisMycobacterium tuberculosis Mycobacterium lepraeMycobacterium leprae Coxiella burnetiiCoxiella burnetii

Activated MacrophagesActivated MacrophagesMacrophages can be activated by antigenMacrophages can be activated by antigen--specific or by nonspecific or by non--specific means. Activation specific means. Activation is an operational term indicating an enhanced is an operational term indicating an enhanced capacity to do inflammatory battle.capacity to do inflammatory battle.

The many faces of macrophage activationThe many faces of macrophage activation

Selective inflammatory cell recruitment by Selective inflammatory cell recruitment by activated macrophagesactivated macrophages

Plasma cellPlasma cell

Resolving chronic inflammationResolving chronic inflammationMixed acute and chronic Mixed acute and chronic

inflammationinflammation

lymphocyteslymphocytes

macrophagemacrophage

Chronic inflammation with infectionChronic inflammation with infection

neutrophilneutrophil

Granulomas and Granulomatous Granulomas and Granulomatous InflammationInflammation

•• Inability to eliminate Inability to eliminate causative agentcausative agent

•• Involves specific and nonInvolves specific and non--specific T cell immunityspecific T cell immunity

•• MycobacteriaMycobacteria

•• FungiFungi

•• ParasitesParasites

FeaturesFeatures CausesCauses

specific T cell immunityspecific T cell immunity•• Recruitment of monocytes, Recruitment of monocytes,

macrophages, and macrophages, and lymphocyteslymphocytes

•• Persist for long periods as Persist for long periods as aggregatesaggregates

•• Foreign BodyForeign Body

•• IdiopathicIdiopathic

Histologic features of Granulomas and Histologic features of Granulomas and Granulomatous InflammationGranulomatous Inflammation

•• Epithelioid histiocytes Epithelioid histiocytes (Secretory Macrophages)(Secretory Macrophages)

•• Giant CellsGiant Cells

•• LymphocytesLymphocytes

•• FibrosisFibrosisFibrosisFibrosis

Abundant pink cytoplasmAbundant pink cytoplasm

Granuloma formationGranuloma formation

A.A. Recruitment of mixed Recruitment of mixed inflammatory cells, driven inflammatory cells, driven by cytokinesby cytokines

B.B. Enrichment in mononuclear Enrichment in mononuclear cells (macrophages, cells (macrophages, ( p g ,( p g ,lymphocytes) organizing lymphocytes) organizing into a clusterinto a cluster

C.C. Fully organized granuloma Fully organized granuloma with fibrosis and disruption with fibrosis and disruption of tissue architectureof tissue architecture

Cytokines and chemokines in immune granuloma formationCytokines and chemokines in immune granuloma formation

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Mycobacterium tuberculosisMycobacterium tuberculosis

H&EH&E H&EH&E

acid fastacid fast

Foamy macrophages (granulomatous)Foamy macrophages (granulomatous)in lepromatous leprosy in lepromatous leprosy ((Mycobacterium lepraeMycobacterium leprae))

Lepromatous leprosyLepromatous leprosy

Interstitial InflammationInterstitial Inflammation

•• nonspecific morphology (chronic nonspecific morphology (chronic nonspecific inflammation)nonspecific inflammation)

•• suggestive of viral, suggestive of viral, mycoplasmamycoplasma, , rickettsial, or spirochetal infectionsrickettsial, or spirochetal infections

Interstitial Interstitial pneumonitispneumonitis

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Rickettsia rickettsiiRickettsia rickettsii

Mycoplasma Mycoplasma pneumoniaepneumoniae

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H&EH&EInfluenza A virusInfluenza A virus

Interstitial Interstitial pneumonitispneumonitis

Cytopathic or Cytoproliferative Cytopathic or Cytoproliferative changeschanges

•• most typical of viral infectionsmost typical of viral infections

•• may be seen with intracellular bacterialmay be seen with intracellular bacterial•• may be seen with intracellular bacterial may be seen with intracellular bacterial infections (e.g. infections (e.g. Chlamydia trachomatisChlamydia trachomatis))

•• angioproliferative responses caused by angioproliferative responses caused by BartonellaBartonella spp.spp.

Human papillomavirus Human papillomavirus –– condylomacondyloma acuminatumacuminatum –– venereal wartsvenereal warts

Chlamydia trachomatis Chlamydia trachomatis cytopathic effectcytopathic effect

Papinicolou (“Pap”) stainsPapinicolou (“Pap”) stains

Cytoproliferative inflammation:Cytoproliferative inflammation:Bacillary angiomatosisBacillary angiomatosis-- Bartonella henselae

H&EH&E silver stainsilver stain

The “Null” reactionThe “Null” reaction

•• absence of inflammatory, necrotizing, or absence of inflammatory, necrotizing, or cytopathic responsescytopathic responsesyy

•• rare with bacterial infectionsrare with bacterial infections•• may occur with neutropenia or immune may occur with neutropenia or immune

compromise due to lack of inflammatory compromise due to lack of inflammatory cells or by rapid, unrestricted bacterial cells or by rapid, unrestricted bacterial growthgrowth

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Vibrio vulnificusVibrio vulnificus with neutropeniawith neutropenia Gram stainGram stain

Bacillus anthracisBacillus anthracis (anthrax)(anthrax)

cutaneouscutaneous

dura materdura materinhalational anthraxinhalational anthrax

Bacterial Infections in Abnormal Hosts•• Physiologic defectsPhysiologic defects

Cystic fibrosis Achlorhydria

Defective inflammatory responseDefective inflammatory response leukocyte adhesion molecule deficiency chronic granulomatous disease

•• Defects in immune functionDefects in immune function complement deficiency, asplenia, susceptibility to

encapsulated bacteria hypogammaglobulinemia > defective opsonization HIV, cancer therapy, corticosteroid or immune

suppressive therapy diminish effective T lymphocyte responses

interferon- receptor deficiencies (recurrent Mycobacteria and Salmonella infections)

The pathogenetic basis of the host-microbe interactions and disease

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Emiliania huxleyiNeorickettsia sennetsu

Rickettsia prowazekii

Anaplasma phagocytophilumHelicobacter pylori

Haemophilus influenzaeStreptococcus pyogenes

Neisseria gonorrhoeaeCoxiella burnetii

Staphylococcus aureus

Enterococcus faecalis

Mycobacterium tuberculosisEscherichia coli

Yersinia pestis

eukaryotic, prokaryotic, and archaea genome sizesn = 866

0.1 1 10 100 1000 10000

genome size (Mbp)

Yersinia pestis

Vibrio vulnificusBacillus anthracis

Klebsiella pneumoniae

Pneumocystis jirovecii

Saccharomyces cerevisiaeCandida albicans

Plasmodium falciparum

Toxoplasma gondii

Brugia malayi

Drosophila simulansHomo sapiensCulex pipiens

Rattus norvegicus

Homo sapiens

Bacterial genomes by COG functional groups

< 50% of recognized COGs > 50% of recognized COGs0 recognized COGs

Influenza virus (V) attached to tracheal cilia (C) and microvilli (M)

Salmonella typhimurium attached to ileal microvilli


Common bacterial adhesins

T3SSs, effector translocation and host cell invasion by Shigella

Dental microcolonies (plaque) of cocciThe biofilm

PicornavirusPicornavirus bindingbinding

Adherence and fusion mechanisms of Adherence and fusion mechanisms of HIV via gp120/gp41HIV via gp120/gp41

Adherence and fusion mechanisms of Adherence and fusion mechanisms of HIV via gp120/gp41HIV via gp120/gp41


Exit and spread of microbesMechanisms of microbial entry post-

adhesion/colonization events


Endothelial cell barriers of the body

CNS, muscle, connective tissues,

skin, lung

Renal glomerulus, intestine, choroid plexus, pancreas, endocrine glands

Liver, spleen, bone marrow


Lymphatic drainage – spread of infection vs. initiation of adaptive immunity


Microbial responses to evade host phagocytosis

Microbe dissemination


Microbial virulence mechanisms: toxins

Bacterial cell walls andmicrobe-associated molecular patterns

(MAMPs)


Pores and hemolysins

phospholipases


Acquisition of exotoxins

Intracellular parasitism by pathogens

• Phagocytosis – opsonized pathogens bind to FcR, CR1,3,4, mannose receptors, or fMLP-receptors and must circumvent host degradation in lysosomes

• Induced endocytosis – pathogen binding to host cell surface followed by bacterial initiation of host cell internalization

• Active invasion – does not require participation of host for internalization

Induced endocytosis in Salmonella

A. S. typhimurium inducing endocytosis in Caco-2 cell

B and C. Actin rearrangements (red) with S. typhimurium (green)

Manipulation of the host’s cytoskeletoninvasion

• Zippering (Listeria)

Manipulation of the host’s cytoskeletonAttachment without invasion

• E. coli– enteropathogenic

(EPEC)

– attachment and effacementeffacement

• Yersinia– inhibition of phagocytosis

Type III secretion mechanism

Type IV secretion systemsType IV secretion systems

Manipulation of the host’s cytoskeletonintracellular motility - actin polymerization

Manipulation of the host’s cytoskeletonintracellular motility - actin polymerization

Shigella enterocolitis

Normal colon enterocolitis

Shigella enterocolitis

enterocolitis

normal colon

Shigella enterocolitis Shigella enterocolitis

Shigella enterocolitis Pneumococcal meningitis

Pneumococcal meningitiscolonization and systemic invasion

• Respiratory mucosa colonizationbacterial factors – phosphorylcholine, CbpA;

polysaccharide capsule; IgA proteaseh t ll f t PAF t li h idhost cell factors – PAF receptor; oligosaccharides

• Invasion into the bloodstreampenetration through mucosal epithelial cellspenetration between mucosal epithelial cells

Pneumococcal meningitisbacteremia / intravascular survival

• Phase shift to upregulate antiphagocytic capsule expression enhances survival in blood

• pneumococci with dense polysaccharide capsules do not adhere well to epithelial surfaces but arenot adhere well to epithelial surfaces but are antiphagocytic

• pneumococci with less polysaccharide capsule and more phosphorylcholine and CbpA adhere well but do not resist phagocytosis well

Pneumococcal meningitis - meningeal invasion

• Need to traverse blood-brain barrierattachment to microvascular endothelial cells

• mediated by CbpA, choline, polysaccharide capsule

• attaches to PAF receptor upregulated with cytokine stimulationwith cytokine stimulation

internalization via PAF receptor leads to endocytosis and:

• intracellular destruction

• recycling to apical surface

• passage to basal surface into CSF enhanced by phase transition

Cell-cell spread of intracellular pathogens• Cell lysis

– Mechanical (Rickettsia prowazekii)

– Necrotic (Plasmodia, Toxoplasma, Trypanosoma, Rickettsia, Shigella)

• Discharge from vacuolesf– Fusion of vacuole with cell

membrane (?Ehrlichia, Chlamydia)

• Direct cell-cell transfer– Propulsion through cell

membrane by actin-based motility (Rickettsia rickettsii, Shigella, Listeria)

Morphologic Tools for Identification of Morphologic Tools for Identification of Microbial InfectionsMicrobial Infections

•• inflammatory response usually stereotypical and inflammatory response usually stereotypical and nonspecificnonspecific

•• inflammation type, special staining characteristics, inflammation type, special staining characteristics, anatomic location, and other cluesanatomic location, and other clues

neutrophils in gastric mucosa > Helicobacter pylori neutrophils in gastric mucosa > Helicobacter pylori

abscess with “sulfur granules” > Actinomycosis (Actinomyces spp.)

caseating granulomas > M. tuberculosis

granulomas with stellate microabscesses > cat scratch disease (Bartonella henselae)

lymphocytic vasculitis > Rocky Mountain spotted fever (Rickettsia rickettsii)

silver stainsilver stain

Helicobacter pyloriHelicobacter pylori gastritisgastritis

H&EH&E

Gram stainGram stainsulfur granulesulfur granule

H&EH&E

actinomycosisactinomycosis

Caseous necrosis in TBCaseous necrosis in TB

H&EH&E

Fluorochrome stainFluorochrome stainSputum acid fast stainSputum acid fast stain

lymphocytic vasculitislymphocytic vasculitisRocky Mountain spotted feverRocky Mountain spotted fever

H&EH&E

H&EH&E immunohistochemistryimmunohistochemistry

cultureculture

Polymerase chain reactionPolymerase chain reaction

H. pyloriH. pylori in situ in situ hybridizationhybridization

S. aureus S. aureus PNA FISHPNA FISH(peptide(peptide--nucleic acid nucleic acid fluorescence in situ fluorescence in situ hybridization)hybridization)

Antigen detection methodsAntigen detection methods1000

1200

1400

1600

1800

y tit

er

Detection of antigen-specific serological responsesPost-infection antibody kinetics

Onset of illness

1 6 12 18 24

Months

0

200

400

600

800

1000

Ant

ibod

y

IgM IgG

Detection of antigen-specific responses

Humoral immunity:• antibody detection• seroconversion or titer increase

Cellular immunity• lymphocyte proliferation• IFN production

Indirect fluorescent antibodyIndirect fluorescent antibody agglutinationagglutination

Protein (Western) Protein (Western) immunoblotimmunoblot

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Infectious disease notes from a helpful teacher