Hepatitis Pathology — Viral and Autoimmune

Viral Hepatitis Mechanisms

• Direct viral cytotoxicity and immune-mediated hepatocellular injury: Viral replication within hepatocytes (HAV, HBV, HCV) or cholangiocytes leads to cytopathic damage, though immunologic responses (CD8+ T cell-mediated) represent the primary mechanism of hepatocellular necrosis. In HBV infection, the host immune response to viral antigens (HBsAg, HBeAg) drives hepatocyte apoptosis through granzyme B and perforin release, explaining why immunocompetent hosts experience more severe acute hepatitis than immunocompromised patients. Innate immunity activation via toll-like receptors (TLRs 3, 7, 9) generates interferon-α/β and pro-inflammatory cytokines (TNF-α, IL-6), perpetuating inflammation.

• Viral persistence and chronic inflammation mechanisms: HBV and HCV achieve chronic infection through viral escape mechanisms—HBV via integration into hepatocyte DNA (up to 50% of hepatocytes in chronic carriers) and rapid mutation in the HBsAg epitope region, while HCV establishes replication in hepatocytes and immune cells with high genetic heterogeneity (quasispecies) preventing antibody neutralization. Persistent antigen stimulation maintains CD4+ and CD8+ T cell activation in portal tracts, driving recruitment of inflammatory cells (lymphocytes, macrophages, plasma cells). HCV's NS5A and NS3/4A proteins directly antagonize interferon signaling (suppression of JAK-STAT pathway), enabling viral persistence.

• Progressive fibrogenesis and cirrhosis development: Hepatic stellate cells (HSCs) undergo activation (transformation to myofibroblasts) in response to inflammatory cytokines (TGF-β, TNF-α) and oxidative stress, depositing excessive type I and III collagen in portal tracts, around hepatocytes (perisinusoidal fibrosis), and bridging portal-to-portal or portal-to-central vein regions. Repeated cycles of hepatocyte necrosis-apoptosis and regeneration create physical disruption of hepatic architecture, progressive obliteration of sinusoidal space, and eventual architectural distortion characteristic of cirrhosis. Hepatocellular carcinoma (HCC) develops through cumulative oncogenic hits: HBV integration mutagenesis, chronic inflammation-induced genomic instability, HCV-mediated oxidative stress, and cirrhosis-related increased hepatocyte proliferation in dysplastic nodules.

Autoimmune Hepatitis Mechanisms

• Loss of immune tolerance and autoimmune activation: Breakdown of regulatory T cell (Treg) function and loss of central/peripheral tolerance permit autoreactive CD4+ and CD8+ T cells to target hepatocyte-associated autoantigens (soluble liver antigen [SLA], liver-kidney microsomal antigen [LKM], anti-smooth muscle antibody [ASMA] epitopes). Molecular mimicry between pathogenic antigens (viral epitopes, environmental antigens) and self-hepatocyte antigens, combined with HLA susceptibility alleles (HLA-DR3, HLA-DR4), drives cross-reactive T cell responses. Impaired Treg suppression through altered IL-2 signaling or reduced FOXP3+ cell frequency perpetuates chronic inflammation.

• Genetic susceptibility and environmental triggers: Strong HLA association (70-80% carry HLA-DR3 or HLA-DR4) predisposes to disease, with HLA-DRB1*03 and DRB1*04 alleles presenting pathogenic peptides to CD4+ T cells. Environmental triggers (viral infections, medications, immunizations) may precipitate disease in genetically predisposed individuals through epitope spreading and bystander activation of hepatocyte-specific T cells.

Viral Hepatitis

• Hepatitis A Virus (HAV)
• Transmission: Fecal-oral route; contaminated food/water
• Epidemiology: Most common cause of acute viral hepatitis worldwide; poor sanitation increases risk
• Natural history: Always self-limited acute hepatitis; no chronic infection; mortality <1% except in elderly and cirrhotic patients

• Hepatitis B Virus (HBV)
• Transmission: Blood/body fluid (percutaneous, sexual, vertical); sexual contact and IVDU are major routes in developed countries
• Chronic infection rate: 90% in neonates, 30% in children <6 years, <5% in immunocompetent adults
• Risk factors: Vertical transmission, multiple sexual partners, MSM, healthcare worker exposure, IVDU, hemodialysis patients
• Oncogenic potential: 30-40% of chronic HBsAg carriers develop HCC (highest among all chronic hepatitis viruses)

• Hepatitis C Virus (HCV)
• Transmission: Blood-to-blood; IVDU accounts for >50% of new infections in developed nations; sexual transmission rare
• Chronic infection rate: 80% of infected individuals develop chronic HCV (highest chronicity rate among hepatitis viruses)
• Genotypes 1a/1b and 3a most common in North America/Europe; genotype 1 associated with worse fibrosis progression
• Extrahepatic manifestations: Cryoglobulinemia, membranoproliferative glomerulonephritis, porphyria cutanea tarda

• Hepatitis D Virus (HDV)
• Obligate dependency on HBV for viral replication; occurs only in HBsAg-positive individuals
• Transmission: Horizontal (blood/sexual) or vertical; endemic in Eastern Europe, Mediterranean, Africa, Amazon basin
• Acceleration of liver disease: Superinfection with HDV in chronic HBV carriers rapidly accelerates to cirrhosis; coinfection slightly less aggressive

• Hepatitis E Virus (HEV)
• Transmission: Fecal-oral; waterborne outbreaks in developing countries
• Clinical course: Self-limited acute hepatitis similar to HAV; fulminant hepatitis in pregnant women (15-25% mortality), particularly in third trimester
• Chronic infection: Rare in immunocompetent hosts; occurs in immunosuppressed transplant recipients
• Zoonotic potential: Transmission from swine, wild boar, deer

Autoimmune Hepatitis

• Type 1 Autoimmune Hepatitis (70-80% of cases)
• Autoantibodies: Anti-smooth muscle antibody (ASMA) and/or anti-nuclear antibody (ANA)
• HLA association: HLA-DR3, HLA-DR4
• Demographics: Female predominance (70%); bimodal age distribution (young adults 15-35 years, older adults >50 years)

• Type 2 Autoimmune Hepatitis (10-15% of cases)
• Autoantibodies: Anti-liver-kidney microsomal antibody (anti-LKM1), often with anti-liver cytosol 1 (anti-LC1)
• Target antigen: Cytochrome P450 2D6 (CYP2D6)
• Demographics: Predominantly children aged 2-14 years; more common in Europe
• Prognosis: More aggressive than Type 1; higher frequency of cirrhosis at presentation (40-60%)

• Type 3 Autoimmune Hepatitis (rare, <5%)
• Autoantibodies: Anti-soluble liver antigen (anti-SLA/LP)
• Often overlaps with Type 1 or Type 2
• Clinical behavior similar to Type 1 but may represent seronegative variant

Acute Hepatitis (Viral or Autoimmune)

• Constitutional symptoms
• Malaise, fatigue, arthralgias (particularly HBV, HCV); myalgias common in HAV and HEV
• Prodromal phase (1-2 weeks): Marked fatigue with non-specific symptoms preceding jaundice
• Anorexia, nausea, vomiting—proportional to inflammation severity
• Morphological correlate: Hepatocyte ballooning, acidophil bodies, and hepatocyte necrosis within lobule increase pro-inflammatory cytokine production (TNF-α, IL-6)

• Jaundice and cholestasis symptoms
• Hyperbilirubinemia (predominantly conjugated/direct) develops after 2-3 weeks of illness in symptomatic patients
• Dark urine, pale/clay-colored stools, pruritus (cholestasis)
• Right upper quadrant discomfort or tenderness (hepatic capsular distension)
• Morphological correlate: Canalicular cholestasis with bile plugs visible on H&E; hepatocyte swelling and sinusoidal space compression elevate hepatic pressure

• Physical examination findings
• Hepatomegaly (firm, non-tender edge); splenomegaly (25-30% of acute HAV; less common in HBV/HCV)
• Absence of spider angiomas, palmar erythema, ascites in uncomplicated acute hepatitis (presence suggests underlying cirrhosis or fulminant failure)
• Icterus (scleral, skin); no petechiae or bleeding in typical acute hepatitis

• Laboratory abnormalities in acute phase
• Markedly elevated transaminases: ALT >1000 IU/L common in acute viral hepatitis (often >2000-3000); ALT>AST (typical, reflects hepatocyte-dominant injury)
• ALP and bilirubin elevation: Mild ALP elevation (1.5-3x ULN) with bilirubin 5-20 mg/dL; cholestatic pattern (ALP>ALT) suggests obstruction or severe injury
• PT/INR prolongation: Reflects synthetic dysfunction and clotting factor depletion; prognostic indicator in acute hepatitis
• Serological markers: HAV IgM (acute), HBsAg/HBeAg with anti-HBc IgM (acute HBV), HCV anti-body/HCV RNA (HCV), elevated immunoglobulin levels (polyclonal IgG elevation in autoimmune hepatitis)

Chronic Hepatitis (HBV, HCV, Autoimmune)

• Insidious onset with minimal symptoms
• Many chronic HBV and HCV patients asymptomatic for years or decades despite active viral replication
• Fatigue, malaise, low-grade fever intermittently reported
• Autoimmune hepatitis often presents with symptomatic acute/subacute hepatitis (60-70%) but insidious chronic hepatitis in others

• Progressive hepatic dysfunction signs
• Ascites, pedal edema (portal hypertension, hypoalbuminemia from diminished hepatic synthesis)
• Spider angiomas, palmar erythema, testicular atrophy (chronic liver disease stigmata from portal hypertension and estrogen excess)
• Hepatosplenomegaly with firm liver edge; splenomegaly reflects portal hypertension-induced splenic congestion
• Gynecomastia, hypotestosteronism (altered estrogen metabolism)
• Jaundice develops late with progressive cholestasis or fulminant deterioration

• Complications of cirrhosis (advanced disease)
• Varices: Hematemesis/melena from esophageal variceal hemorrhage (most common cause of death in cirrhotic patients)
• Hepatic encephalopathy: Altered mental status, asterixis, personality changes (elevated ammonia from portosystemic shunting and reduced hepatic urea cycle)
• Spontaneous bacterial peritonitis (SBP): Abdominal pain, fever, ascites worsening
• Hepatorenal syndrome: Progressive azotemia, oliguria despite normal renal pathology (vasoconstriction from splanchnic vasodilation and systemic vasopressin excess)
• Hepatocellular carcinoma: RUQ pain, weight loss, palpable mass; primarily in cirrhotic livers with chronic HBV/HCV

Fulminant Hepatitis (Acute Liver Failure)

• Severe coagulopathy and encephalopathy
• INR >1.5 in acute hepatitis without prior liver disease = fulminant hepatic failure
• Grade 3-4 hepatic encephalopathy: Severe confusion, coma
• Morphological correlate: Massive hepatocellular necrosis with loss of >50% of hepatic mass; submassive necrosis (50%) may allow recovery if regeneration proceeds

• Multi-organ dysfunction
• Acute kidney injury (hepatorenal syndrome type 1 vs. direct viral injury in HEV)
• Coagulopathy (prolonged PT from lack of factor II, VII, IX, X synthesis)
• Hypo/hyperglycemia, acidosis
• High mortality: 20-90% depending on etiology (HEV particularly dangerous in pregnancy; HAV/HBV <1-5% in immunocompetent; autoimmune hepatitis 10-20%)

Histological Features

• Portal inflammation and interface hepatitis
• Mononuclear cell infiltrates (predominantly CD8+ T lymphocytes, CD4+ T cells, macrophages) in portal tracts; plasma cells prominent in autoimmune hepatitis
• Interface hepatitis (piecemeal necrosis): Inflammatory cells breach limiting plate and extend into adjacent periportal hepatocytes, causing hepatocyte apoptosis and dropout
• Grade of inflammation (Knodell/Ishak score): Grade 1 (portal only) to Grade 4 (bridging necrosis with portal-to-portal or portal-to-central involvement)
• Viral hepatitis typically shows portal inflammation with few or no plasma cells; autoimmune hepatitis characteristically shows prominent plasma cell infiltration (activated B cells, immunoglobulin-secreting plasma cells)

• Hepatocyte necrosis patterns
• Lobular disarray: Loss of normal hepatocyte cords and sinusoidal alignment
• Hepatocyte ballooning (cytoplasmic swelling, pale cytoplasm, displaced nucleus)—represents cellular edema from mitochondrial dysfunction
• Acidophil bodies (Councilman bodies): Apoptotic hepatocytes appearing as round, eosinophilic bodies; hallmark of viral hepatitis but non-specific
• Syncytia formation: Multinucleated giant hepatocytes (more common in HBV)
• Spotty/focal necrosis: Scattered individual hepatocyte apoptosis throughout lobule (typical acute hepatitis)
• Bridging necrosis: Collapse of reticulin framework connecting portal-to-portal or portal-to-central regions, indicating severe active disease; prognostic marker for progression to cirrhosis

• Stage of fibrosis (Metavir or Ishak staging)
• Stage 0: No fibrosis (normal lobular architecture)
• Stage 1: Portal fibrosis without bridging
• Stage 2: Bridging fibrosis (portal-to-portal or portal-to-central)
• Stage 3: Bridging fibrosis with occasional nodules (early cirrhosis)

Immediate stabilisation (acute/fulminant hepatitis)

• Assess for acute liver failure first: any encephalopathy plus INR >1.5 in a patient without known cirrhosis mandates ICU admission and immediate transfer to a transplant centre — the AASLD acute liver failure guidance stresses early referral, since deterioration outpaces recovery. Treat hypoglycaemia, correct only clinically significant bleeding (do not reflexively reverse INR — it is the prognostic marker), and manage cerebral oedema.
• Supportive care for HAV and HEV: self-limited; no antiviral is indicated. Post-exposure prophylaxis for HAV contacts is vaccine (± immune globulin in the very young, elderly, or immunocompromised) per CDC/ACIP.

First-line antiviral therapy

• Chronic HBV — nucleos(t)ide analogues: entecavir or tenofovir (TDF/TAF) are AASLD first-line for eligible patients (elevated ALT with high HBV DNA, cirrhosis, or immunosuppression). They suppress reverse transcription of pregenomic RNA but do not clear cccDNA, so therapy is typically long-term. Peginterferon alfa is an alternative finite-duration option.
• Chronic HCV — pangenotypic direct-acting antivirals: sofosbuvir/velpatasvir or glecaprevir/pibrentasvir per AASLD/IDSA HCV guidance; cure is defined as SVR12 (undetectable HCV RNA 12 weeks post-treatment). Nearly all infected adults warrant treatment.
• HDV: requires HBV suppression; peginterferon alfa is the historical option and responses are poor.

Autoimmune hepatitis

• Corticosteroid induction ± thiopurine maintenance: prednisone (or budesonide in non-cirrhotic disease) with azathioprine added as a steroid-sparing agent, per AASLD. Check thiopurine metabolism (TPMT/NUDT15) before azathioprine. Second-line: mycophenolate or a calcineurin inhibitor.

Definitive management

• Liver transplantation for fulminant failure meeting King's College criteria and for decompensated cirrhosis.

Contraindicated / cautions

• Protease-inhibitor-containing DAAs (glecaprevir/pibrentasvir) in decompensated cirrhosis.
• Interferon in decompensated cirrhosis and in autoimmune hepatitis (may flare disease).
• Ribavirin and mycophenolate in pregnancy — both teratogenic.
• Abrupt withdrawal of nucleos(t)ide analogues, which can precipitate a severe hepatitis flare.

Emergencies

• Fulminant hepatic failure: massive/submassive necrosis loses the functional hepatocyte mass needed for coagulation-factor and urea synthesis. Signalled by rising INR with falling transaminases (hepatocyte exhaustion, not recovery) plus encephalopathy. Immediate transplant-centre transfer.
• Variceal haemorrhage: portosystemic collaterals from sinusoidal portal hypertension; hematemesis/melena with hypotension. Requires vasoactive therapy, antibiotic prophylaxis, and urgent endoscopy.
• Spontaneous bacterial peritonitis: translocation across a congested gut; ascitic PMN count ≥250/mm³ is the diagnostic signal.
• HBV reactivation: withdrawal of immune control (rituximab, chemotherapy, high-dose steroids, or abrupt nucleos(t)ide analogue cessation) allows cccDNA-driven replication; abrupt ALT and HBV DNA rise, sometimes with liver failure. FDA carries a boxed warning for HBV reactivation during HCV DAA therapy in coinfected patients — screen HBsAg/anti-HBc before treating.

Chronic disease complications

• Cirrhosis and portal hypertension: stellate-cell collagen deposition and bridging fibrosis obliterate sinusoidal flow; ascites, splenomegaly, thrombocytopenia.
• Hepatocellular carcinoma: HBV integration mutagenesis plus regenerative proliferation. AASLD recommends surveillance ultrasound (± AFP) roughly every six months in cirrhosis and in selected chronic HBV carriers; a new arterially enhancing nodule with washout is the signal.
• Immune-complex disease: HCV mixed cryoglobulinemia with palpable purpura, neuropathy, and membranoproliferative GN (low C4); HBV with polyarteritis nodosa.

Treatment-related

• Tenofovir disoproxil fumarate: proximal tubular injury (Fanconi syndrome, phosphate wasting) and reduced bone density — monitor creatinine/phosphate.
• Azathioprine: dose-independent myelosuppression via TPMT/NUDT15 deficiency (cytopenias), pancreatitis, and long-term lymphoma/non-melanoma skin cancer risk.
• Chronic corticosteroids: hyperglycaemia, osteoporosis, adrenal suppression on withdrawal.
• Ribavirin: dose-dependent haemolytic anaemia.

• Ground-glass hepatocytes: finely granular, homogeneous eosinophilic cytoplasm from HBsAg-stuffed smooth endoplasmic reticulum — pathognomonic-flavoured for chronic HBV, not acute HBV and never HCV. Confirm with HBsAg immunostain.
• Councilman (acidophil) bodies: shrunken, deeply eosinophilic apoptotic hepatocytes. Seen in viral hepatitis, but also yellow fever and other injuries — a non-specific finding, so do not use them to name a virus.
• The window period: HBsAg gone, anti-HBs not yet present — the only positive marker is anti-HBc IgM. Isolated anti-HBs = vaccinated; anti-HBs plus anti-HBc = resolved natural infection.
• Best next step after a positive HCV antibody: HCV RNA by PCR, since antibody persists after cure or spontaneous clearance and cannot distinguish active from past infection.
• The autoimmune hepatitis triad examiners test: interface hepatitis with plasma-cell-rich portal infiltrate + polyclonal hypergammaglobulinemia (high IgG) + ANA/ASMA (type 1) or anti-LKM1 against CYP2D6 (type 2, children). Steroids, not antivirals.
• HEV in pregnancy: fulminant hepatitis with high mortality in the third trimester; the stem is a pregnant traveller with contaminated water exposure.
• HDV requires HBsAg: superinfection of a chronic carrier causes an abrupt flare and rapid cirrhosis; coinfection is usually self-limited with the HBV.
• Bridging necrosis is the histologic marker of severe disease that predicts progression to cirrhosis — distinguish it from spotty necrosis, which is routine acute hepatitis.
• Common distractor: HBV can cause hepatocellular carcinoma without cirrhosis (integration is directly mutagenic); HCV-related HCC essentially always arises in a cirrhotic liver.
• Do not attribute jaundice pattern wrongly: acute viral hepatitis gives ALT > AST; AST:ALT ≈ 2:1 points to alcohol instead.