Immune Reconstitution Inflammatory Syndrome

• Thymic and peripheral immune reconstitution: Following ART initiation or immune recovery, CD4+ T-cell count increases through two mechanisms: rapid redistribution of sequestered T cells from lymphoid tissues (within days to weeks) and slower thymic-derived naive T-cell production (weeks to months). This restoration occurs despite continued presence of opportunistic pathogen antigens from infections established during profound immunosuppression. The newly expanded pathogen-specific CD4+ T-cell population mounts robust cellular immune responses characterized by interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and interleukin-2 (IL-2) production. Paradoxically, this "protective" immune response becomes pathogenic, generating excessive inflammation that causes organ damage and clinical deterioration despite declining or stable pathogen burden.

• Antigen burden and mycobacterial factors: The magnitude of inflammatory response correlates directly with antigen load at the time of immune reconstitution. Tuberculosis-associated IRIS exemplifies this mechanism: mycobacterial antigens (including cell wall lipoproteins and heat shock proteins) accumulate in macrophages and tissue during TB treatment; when CD4+ T cells recover, they recognize these antigens through T-cell receptor (TCR) engagement and MHC-II presentation, triggering massive TNF-α and IL-6 production by activated macrophages. Mycobacterial lipoproteins additionally engage TLR2/TLR6 complexes on innate immune cells, amplifying inflammatory responses. The timing of TB diagnosis relative to ART initiation significantly influences IRIS risk: delayed TB diagnosis (unrecognized during severe immunosuppression) results in higher mycobacterial burden and greater IRIS risk compared to cases where TB diagnosis precedes or immediately follows ART initiation with lower organism burden.

• Immune checkpoint dysregulation and regulatory T-cell dysfunction: During profound immunosuppression, regulatory T cells (Tregs) maintain immune tolerance to pathogenic antigens through IL-10 and TGF-β production. Upon immune reconstitution, CD4+ effector T-cell recovery outpaces Treg restoration, disrupting the Treg:effector ratio and eliminating tolerogenic control mechanisms. Additionally, programmed cell death-1 (PD-1) and cytotoxic T-lymphocyte antigen-4 (CTLA-4) expression—which normally restrain excessive T-cell responses—remain upregulated on newly recovered T cells, but their ligation by PD-L1/L2 and CD80/CD86 ligands becomes insufficient to constrain the heightened inflammation. The ratio of naïve to memory CD4+ T cells also influences IRIS: patients with low CD4+ counts at ART initiation possess predominantly naïve T-cell repertoires that require antigen-specific priming before mounting responses, whereas patients with higher baseline CD4+ counts possess pre-existing memory T-cell populations capable of rapid, non-specific inflammatory activation.

• Innate immune contribution and inflammasome activation: Beyond adaptive immunity, IRIS involves significant innate immune amplification. Pathogen-associated molecular patterns (PAMPs) from mycobacteria, cryptococcal antigens, and cytomegalovirus (CMV) activate pattern recognition receptors (TLRs, NOD-like receptors) on dendritic cells, macrophages, and neutrophils, triggering NF-κB and MAPK signaling cascades. Mycobacterial and fungal products specifically activate the NLRP3 inflammasome, leading to caspase-1 activation and maturation of IL-1β and IL-18, potent drivers of Th1 and Th17 differentiation. The kinetics of immune reconstitution relative to antimicrobial therapy determine inflammasome activation: if ART initiation precedes or accompanies adequate antimicrobial therapy, high pathogen burden persists while immune function recovers, maximizing PAMP exposure to recovering innate immunity. This explains why paradoxically, early TB therapy initiation combined with early ART (≤2 weeks) increases TB-IRIS risk compared to delayed ART initiation in patients with concurrent TB and CD4 <50 cells/μL—the inflammation from simultaneous pathogen killing and immune recovery proves excessive.

• Tissue-specific inflammation and barrier dysfunction: IRIS pathology involves not only aberrant immune activation but also breakdown of tissue barriers and recruitment of effector cells to infection sites. TNF-α production by activated macrophages increases vascular permeability through VE-cadherin disruption and VEGF upregulation, promoting leukocyte extravasation. In TB-IRIS affecting the central nervous system (tuberculous meningitis-IRIS), TNF-α and IL-6 production damages the blood-brain barrier, increasing intracranial pressure and enhancing cerebrospinal fluid inflammation. Similarly, in pulmonary TB-IRIS, Th1 cell infiltration into lung granulomas and production of TNF-α, IFN-γ, and matrix metalloproteinases cause granuloma maturation with central caseous necrosis, radiologically apparent as new infiltrates or paradoxical enlargement of pre-existing lesions despite microbiological improvement.

• HIV infection with CD4+ <50 cells/μL (pathogen-associated IRIS): The most prevalent IRIS population includes patients initiating ART with unrecognized or partially treated opportunistic infections. Tuberculosis-associated IRIS is the most common cause of TB-IRIS, occurring in 1-36% of TB-HIV coinfected patients depending on baseline CD4+ count, with incidence highest when TB is diagnosed concurrent with or shortly after ART initiation in patients with CD4+ <100 cells/μL. Cryptococcal meningitis-IRIS affects 5-54% of CM survivors restarting ART and represents one of the most severe IRIS manifestations, characterized by recurrent meningitis despite negative cerebrospinal fluid cultures and fluconazole continuation. Cytomegalovirus (CMV) immune recovery uveitis occurs in 0.2-50% of CMV-retinitis patients initiating ART, typically 4-12 weeks after immune reconstitution begins, manifesting as anterior chamber inflammation despite halted viral replication. Mycobacterium avium complex (MAC) disease-IRIS emerges in patients with CD4+ <50 cells/μL who begin MAC prophylaxis concurrent with ART but with persistent MAC burden in tissue macrophages. Other less common pathogens triggering IRIS include herpes simplex virus (HSV), varicella zoster virus (VZV), Pneumocystis jirovecii pneumonia (PCP), and toxoplasmosis.

• Non-pathogen-associated IRIS (autoimmune and idiopathic): Approximately 25% of IRIS cases lack identified opportunistic pathogen triggers, instead manifesting as de novo autoimmune phenomena termed "idiopathic IRIS" or "non-pathogen-associated IRIS." These include immune-mediated conditions such as acute inflammatory demyelinating polyradiculoneuropathy (AIDP), Guillain-Barré syndrome, polymyositis, systemic lupus erythematosus (SLE)-like disease with anti-dsDNA antibodies, immune thrombocytopenic purpura (ITP), autoimmune hemolytic anemia, and Graves' disease with thyroid storm. Malignancy-associated IRIS includes lymphoma enhancement and rapid progression of Kaposi sarcoma (KS) immune recovery syndrome, characterized by paradoxical KS worsening despite HHV-8 viral load reduction. The pathophysiology likely involves restoration of self-reactive T-cell responses previously suppressed during immunodeficiency.

• Underlying severe immunosuppression severity and CD4+ nadir: The most robust predictor of IRIS risk is CD4+ T-cell count at ART initiation; risk is highest with counts <50 cells/μL, moderate with counts 50-100 cells/μL, and minimal above 100 cells/μL. The absolute CD4+ count at IRIS onset typically ranges 20-150 cells/μL, suggesting a threshold effect where immune function reaches sufficient levels for pathogen-specific response but remains too low to maintain immune homeostasis and regulatory T-cell function. Rapid CD4+ count increase following ART (>50-100 cells/μL increase in first month) paradoxically increases IRIS risk, likely reflecting brisk expansion of antigen-specific T-cell clones.

• Timing of immune reconstitution relative to pathogen control: The interval between ART initiation and adequate antimicrobial therapy initiation influences IRIS risk. Early TB therapy initiation combined with early ART increases TB-IRIS risk compared to delayed ART initiation in TB-HIV coinfection with CD4+ <50 cells/μL, reflecting simultaneous pathogen killing and immune recovery. Conversely, delayed TB diagnosis with continued high mycobacterial burden at ART initiation also increases IRIS risk. The "sweet spot" reducing TB-IRIS is moderate delay in ART initiation (8 weeks) in patients receiving TB therapy, allowing some pathogen burden reduction before maximum immune recovery.

• Additional risk factors: Male gender, higher baseline viral load, and rapid increase in CD4+ count are associated with higher IRIS incidence. Genetic factors including HLA alleles (HLA-B*35 protective, HLA-B*27 associated with IRIS) and polymorphisms in TNF-α, IL-6, and IL-10 promoter regions influence IRIS susceptibility. Inflammatory markers at baseline (elevated C-reactive protein, IL-6) predict IRIS development. Inadequate antimicrobial therapy at time of immune reconstitution increases risk, as persistent pathogen burden provides continued antigenic stimulus to recovering immune cells.

• Tuberculous IRIS (TB-IRIS): The most common IRIS presentation includes pulmonary, lymph node, and central nervous system manifestations. Pulmonary TB-IRIS manifests as new or worsening respiratory symptoms (cough, dyspnea, chest pain) accompanied by new pulmonary infiltrates, focal consolidation, or cavitary lesions on chest X-ray despite appropriate TB therapy and declining mycobacterial burden. Sputum smears and cultures show declining or negative results, distinguishing IRIS from treatment failure. Lymph node TB-IRIS presents as rapid enlargement of mediastinal, hilar, or peripheral lymph nodes with development of suppuration and fistulization, sometimes progressing to abscess formation with systemic inflammation. Tuberculous meningitis-IRIS represents the most severe manifestation, occurring in 5-10% of TB-meningitis patients receiving ART and characterized by recurrent meningitis symptoms (fever, headache, meningismus, altered mental status) despite negative cerebrospinal fluid cultures and appropriate TB and dexamethasone therapy. CSF shows persistent lymphocytic pleocytosis (50-500 cells/μL), elevated protein (100-500 mg/dL), and low glucose despite sterilization of CSF. Neuroimaging reveals basilar enhancement, hydrocephalus, and cranial nerve involvement.

• Cryptococcal meningitis (CM)-IRIS: Presents as recurrent meningitis symptoms (fever, headache, photophobia, neck stiffness) 2-16 weeks after ART initiation in patients with known CM history, despite appropriate fluconazole therapy and negative CSF cryptococcal antigen or culture. CSF inflammatory markers (white blood cell count, protein) worsen paradoxically despite declining organism burden. Intracranial pressure increases dramatically, requiring aggressive cerebrospinal fluid drainage. Some patients develop cryptococcal immune recovery uveitis (CRIU) with anterior chamber inflammation and vision-threatening sequelae. Mortality from CM-IRIS reaches 25-40%, making this among the most serious IRIS manifestations.

• CMV immune recovery uveitis: Manifests 4-12 weeks after ART initiation in patients with prior CMV-retinitis or immune recovery uveitis in those with history of severe CMV disease. Symptoms include floaters, photopsia, blurred vision, and photophobia from anterior chamber inflammation (keratic precipitates, anterior chamber cells, hypopyon). Fundoscopic examination reveals inflammatory response in previously stable CMV lesions, granulomatous anterior uveitis, and vitritis inflammation. Notably, retinal lesions show no new viral replication (viral load undetectable in aqueous humor), confirming immune-mediated pathogenesis. Vision-threatening complications include posterior synechiae, cataract formation, and glaucoma.

• MAC disease-IRIS: Presents as fever, abdominal pain, and diarrhea in patients with disseminated MAC disease (CD4+ <50 cells/μL) receiving both MAC prophylaxis and ART. Lymph node enlargement, hepatosplenomegaly, and occasional abscess formation occur despite declining mycobacterial burden in blood and tissue. Granulomas appear in previously sterile tissues as immune function recovers.

• PCP-IRIS: Manifests as acute respiratory deterioration weeks after PCP treatment completion and ART initiation, with new or worsening dyspnea, fever, and hypoxemia despite negative sputum induction studies. High-resolution CT shows new ground-glass opacities or consolidation unrelated to continuing Pneumocystis growth. Bronchoalveolar lavage may show minimal organism burden but marked inflammatory infiltrate.

• Non-pathogen-associated IRIS presentations: Autoimmune IRIS manifests with typical autoimmune disease features including rash (lupus-like or polyarthritis-associated), neurological symptoms (Guillain-Barré syndrome with ascending paralysis), or constitutional symptoms. Grave's disease thyroid storm presents with thyrotoxicosis, atrial fibrillation, and hemodynamic instability. Lymphoma-IRIS shows paradoxical lymph node enlargement and worsening constitutional symptoms despite chemotherapy response.

• Constitutional symptoms and laboratory findings: Most IRIS presentations include fever (low-grade to high spiking), night sweats, fatigue, and weight loss reflecting systemic inflammation. C-reactive protein and inflammatory cytokines (IL-6, TNF-α, IFN-γ) are markedly elevated. Leukocytosis with left shift is common. Lymph node enlargement, hepatosplenomegaly, and edema reflect regional and systemic inflammation.

• Timing of IRIS onset: TB-IRIS typically occurs within 2-8 weeks of ART initiation, with earlier onset in patients with CD4+ <20 cells/μL. CM-IRIS develops later (median 6-10 weeks) after ART initiation. CMV-IRIS onset is more variable (4-12 weeks). Non-pathogen IRIS timing is most variable but generally occurs weeks to months after immune reconstitution.

Immediate priorities

• Exclude the mimics before treating: per the DHHS/NIH/CDC/IDSA Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV, IRIS is a diagnosis of exclusion — antimicrobial failure or drug resistance, a second undiagnosed opportunistic infection, drug hypersensitivity (abacavir, TMP-SMX), and non-adherence must be ruled out first.
• Airway, ICP, and oxygenation: suppurative mediastinal/cervical nodes causing tracheal compression, raised intracranial pressure in CNS IRIS, and hypoxemic respiratory failure are emergencies requiring intensive care, serial therapeutic lumbar punctures (cryptococcal IRIS), and airway protection.

First-line therapy

• Continue ART: the DHHS OI panel recommends not interrupting ART in nearly all cases, because IRIS is self-limited while ART interruption risks viral rebound, CD4 decline, and resistance. Interruption is reserved for life-threatening, steroid-refractory CNS IRIS.
• Continue and optimize antimicrobial therapy: the inciting pathogen is being controlled, not escaping — full-course anti-TB therapy, fluconazole, ganciclovir/valganciclovir, or macrolide-based MAC therapy is continued unchanged.
• NSAIDs: sufficient for mild disease (fever, self-limited adenitis).
• Corticosteroids: for moderate-to-severe IRIS. Prednisone (roughly 1.5 mg/kg/day tapered over about 4 weeks) is supported by a randomized trial in paradoxical TB-IRIS (Meintjes) and is endorsed by the DHHS OI guidelines; dexamethasone is preferred for CNS involvement. Steroid dose is increased when rifampin is coadministered because of CYP3A4 induction.

Escalation and second-line

• TNF-α blockade (infliximab), thalidomide, and IL-1 blockade (anakinra) are salvage options in steroid-refractory or steroid-dependent CNS TB-IRIS, supported only by case series.

Procedural/definitive management

• Drainage: needle aspiration of suppurative nodes or cold abscesses; ventriculoperitoneal shunt or external ventricular drain for IRIS hydrocephalus; intravitreal/periocular steroid or vitrectomy for immune recovery uveitis.

Prevention and contraindications

• ART timing: within 2 weeks for most OIs and for TB with CD4 <50 cells/µL; deferral to ~4–6 weeks in cryptococcal meningitis (COAT trial) and deferral in tuberculous meningitis, per DHHS.
• Avoid corticosteroids in Kaposi sarcoma–associated IRIS — they worsen KS.
• Adjunctive steroids are not used during cryptococcal meningitis induction therapy (harmful in CryptoDex).

Neurologic — the highest-mortality group

• Raised intracranial pressure and herniation (emergency): cytokine-driven blood–brain barrier breakdown plus impaired CSF outflow; signaled by worsening headache, vomiting, papilledema, bradycardia with hypertension, or declining consciousness with markedly elevated opening pressure on lumbar puncture. Most characteristic of cryptococcal IRIS, which carries the highest case fatality of the IRIS syndromes.
• Hydrocephalus and cranial neuropathies: basilar exudate and arachnoiditis in tuberculous meningitis IRIS; signaled by new ventriculomegaly and basilar enhancement on imaging, or new sixth/seventh nerve palsy.
• Stroke and myeloradiculopathy: inflammatory vasculitis of perforating vessels or intramedullary tuberculomas; signaled by focal deficit or new paraparesis with bladder involvement.
• Guillain–Barré syndrome in non-pathogen-associated IRIS (emergency if vital capacity falls): ascending weakness with areflexia progressing to neuromuscular respiratory failure.

Respiratory and mechanical

• Hypoxemic respiratory failure/ARDS (emergency): granuloma maturation with alveolar inflammatory flooding; signaled by rising oxygen requirement with new infiltrates but negative sputum smears.
• Airway or superior vena cava compression (emergency): rapidly enlarging mediastinal nodes; signaled by stridor, positional dyspnea, or facial plethora.
• Suppurative lymphadenitis with sinus tract or fistula formation: caseation and rupture of nodes into skin, pericardium, or bronchus.

Ocular

• Vision loss from immune recovery uveitis: cystoid macular edema, epiretinal membrane, posterior synechiae, cataract, and secondary glaucoma from sustained intraocular inflammation despite undetectable CMV in aqueous humor.

Treatment-related

• Corticosteroid harms: hyperglycemia, hypertension, adrenal suppression, steroid psychosis, avascular necrosis, and reactivation of latent infection — herpesviruses, and Strongyloides hyperinfection, which can present as gram-negative sepsis and is an emergency.
• Kaposi sarcoma progression with steroids: glucocorticoid-driven HHV-8 lytic gene activation; signaled by rapid mucocutaneous or pulmonary KS worsening.
• ART interruption complications: viral rebound, CD4 decline, and archived resistance mutations if ART is inappropriately stopped.
• Hepatic failure from hepatitis B/C IRIS: immune-mediated hepatocyte lysis; signaled by transaminase flare with rising bilirubin and INR.

• The defining paradox: clinical worsening while the HIV viral load is falling and the CD4 count is rising. If the stem says "deteriorated 3 weeks after starting ART" with an improving viral load, the answer is IRIS, not treatment failure.
• Two flavors: paradoxical IRIS = worsening of a known, already-treated opportunistic infection; unmasking IRIS = a previously subclinical infection erupting after ART. Examiners test the distinction.
• Single best next step is almost always "continue ART" plus continue the antimicrobial and add corticosteroids if severe. Per the DHHS/NIH/CDC/IDSA opportunistic infections guidelines, ART interruption is reserved for life-threatening CNS disease.
• Prednisone is the evidence-based agent for paradoxical TB-IRIS (randomized trial data), tapered over about a month; use dexamethasone for CNS involvement. Steroid dose must be increased if the patient is on rifampin (CYP3A4 induction).
• CD4 <50 cells/µL at ART start is the single strongest risk factor, and the association most often tested is TB and cryptococcal meningitis with ART timing: start ART within 2 weeks for most OIs, but defer about a month in cryptococcal meningitis (COAT trial) and in tuberculous meningitis.
• Sterile inflammation is the buzzword: negative CSF cryptococcal culture with rising CSF white cells and opening pressure; negative sputum smear with new infiltrates; undetectable CMV in aqueous humor with florid immune recovery uveitis.
• Do not give steroids in Kaposi sarcoma–associated IRIS — they accelerate KS. This is the classic "steroids are always the answer" trap.
• Common distractors to reject: drug-resistant TB or antimicrobial failure (cultures are becoming negative, not persistently positive), a new opportunistic infection, and drug hypersensitivity (abacavir, TMP-SMX) — the latter presents with rash/fever without organ-specific inflammation at a prior infection site.