01From immune activation to neurodevelopmental change
The autism cascade model is a systems-biology framework that maps the sequential biological events connecting upstream immune activation to downstream neurodevelopmental change. It is not a single-gene or single-pathway model. It is a convergence model — one that explains how multiple upstream founding conditions (gut pH dysregulation, infections, environmental exposures, genetic susceptibility) produce a common downstream outcome through a shared biological mechanism: the silencing of somatostatin-14 (SST-14) interneurons.
The cascade proceeds through five levels, converging on a single mechanistic node. Each level is supported by published, peer-reviewed research. The full integrated model has not yet been validated in a single large clinical trial — which is precisely what this initiative exists to address. The complete cascade, including the upstream gut-pH and opioid-peptide founding conditions, is detailed in The Anatomy of Autism.
The Autism Cascade — Five Levels from Trigger to Regression
▶ IMIG / IVIG Entry Point
Level 1 — Gut Barrier Failure & Immune Activation
Founding conditions (gut pH dysregulation, opioid peptide accumulation, genetic susceptibility) compromise the intestinal barrier, allowing bacterial lipopolysaccharide (LPS) into systemic circulation. LPS drives sustained elevation of pro-inflammatory cytokines — principally IFN-γ, TNF-α, and IL-6 — and generates neuronal surface autoantibodies. This is where immunoglobulin therapy acts: suppressing the cytokine and autoantibody burden before the downstream cascade loads.
IMIG intervenes here — upstream of everything that follows
Level 2
IDO1 Activation & Kynurenine Pathway Diversion
IFN-γ upregulates indoleamine 2,3-dioxygenase 1 (IDO1), the rate-limiting enzyme in the kynurenine pathway. Tryptophan — the sole precursor to serotonin — is diverted away from normal metabolism into the kynurenine pathway, measurable as an elevated kynurenine-to-tryptophan (K:T) ratio. Quinolinic acid (QUIN) accumulates as a downstream kynurenine metabolite. QUIN is a potent NMDA receptor agonist.
Level 3
SST-14 Interneuron Silencing — The Convergent Node
The same cytokines activate NF-κB inside somatostatin-14 (SST-14) interneurons — the GABAergic cells that coordinate the brain's neuropeptide signaling. NF-κB competes directly with CREB for a shared co-activator (CBP) and recruits HDAC enzymes to compact the chromatin at the SST-14 gene promoter, silencing SST-14 gene transcription. Circulating autoantibodies against neuronal surface proteins compound this by jamming SST-14 receptor signaling directly. This transcriptional suppression is the mechanism immunoglobulin therapy targets most directly — clear the cytokine and autoantibody burden, and CREB can resume driving SST-14 expression.
Level 4
Excitotoxic & Metabolic Pressure on the Same Interneurons
In parallel with the transcriptional arm, QUIN-driven NMDA receptor overactivation forces calcium into SST-14 interneurons faster than their mitochondria can buffer it. These cells fire tonically at high frequency and are disproportionately vulnerable to this energy demand. Downstream kynurenine metabolism also consumes NAD⁺ faster than chronic IDO1 activation can replace it, compounding the energy deficit. Where Level 3 silences SST-14 gene expression, this arm can exhaust the interneuron's capacity to fire even after transcription is restored — the biomarker distinction between the reversible early state and the state requiring metabolic, not just immunological, support.
Level 5
Neuropeptide Cascade Disruption & the Observable Phenotype
Once SST-14 output falls below functional threshold, the neuropeptide systems it coordinates — oxytocin, VIP, and secretin — lose their upstream timing signal simultaneously, producing the social, sensory, sleep, gastrointestinal, and motor features of the phenotype cluster. SST-14 silencing also removes the anti-inflammatory tone SST-14 normally exerts on microglia, allowing astrocyte A1 polarisation and further excitotoxic pressure — a self-reinforcing loop. In children with profound ASD, this state has typically been established over years of cumulative inflammatory loading.
Section 02 — The SST-14 Recovery Argument
02Why recovery requires sustained suppression — not periodic intensity
The most clinically significant implication of the cascade model for immunoglobulin therapy is the SST-14 transcriptional recovery timeline. SST-14 silencing is not a fixed state — it persists only as long as NF-κB continues winning the competition with CREB for CBP at the SST-14 gene promoter. Relieving that competition requires not just a brief drop in cytokines, but a sufficiently sustained reduction that CREB can reliably out-compete NF-κB and SST-14 transcription can resume.
The timescales involved are measured in weeks, not days. CREB-driven SST-14 expression, and the downstream BDNF-dependent synaptic remodelling it enables, operate on timescales of weeks to months. This creates a specific prediction about IVIG's oscillating pharmacokinetic profile.
IVIG peak — acute cytokine suppression
IFN-γ, TNF-α, and IL-6 fall. IDO1 activity decreases. Kynurenine pathway flux reduces. NF-κB activity inside SST-14 interneurons drops, easing its competition with CREB for CBP. Parents and clinicians observe behavioural improvements as SST-14 transcription begins to recover.
IVIG trough — cytokine rebound
Serum IgG returns toward pre-infusion levels. Inflammatory cytokines begin rising again. IDO1 reactivates. NF-κB regains the upper hand over CREB at the SST-14 promoter before transcription has stabilised. The partial recovery achieved in weeks 1–2 is interrupted before completion. Gains plateau or partially reverse — a pattern documented in at least four independent IVIG studies.
IMIG steady-state — the sustained window the biology requires
IMIG's slower absorption profile produces a sustained IgG elevation without the sharp trough. Cytokine and autoantibody suppression is maintained continuously rather than periodically. CREB is given the uninterrupted window it needs to reliably out-compete NF-κB for CBP and drive stable SST-14 transcription. CREB/BDNF-dependent plasticity can re-engage. The six-month minimum trial duration is derived from this timeline — it is the threshold at which cascade recovery becomes measurable.
The Pharmacokinetic Argument
IMIG's lower peak is not a limitation — it is the feature
IVIG's high serum IgG peak produces dramatic early responses, which is why the clinical signal in the literature is so clear. But the trough that follows may be working against the very biology IVIG is trying to restore. IMIG never reaches IVIG's peak — but it never drops as far. For cascade biology, where the therapeutic target is weeks of consistently reduced neuroinflammation rather than periodic peaks of immune suppression, IMIG's steady-state profile is mechanistically preferable, not merely more convenient.
Section 03 — PANS as Mechanism Validation
03Why the PANS result is critical for the ASD argument
Pediatric Acute-onset Neuropsychiatric Syndrome (PANS) is a condition in which autoantibodies — often triggered by streptococcal or other infections — target basal ganglia structures, producing acute behavioural regression, OCD, and neuropsychiatric symptoms. Its mechanism is well-characterised: autoantibody-mediated neuroinflammation producing acute-onset CNS dysfunction. It is, in a meaningful sense, a clean experimental model for the immune-neurological interface — the same autoantibody-mediated surface receptor jamming that compounds transcriptional SST-14 silencing in the ASD cascade (Level 3 above).
Why PANS Validates the ASD Mechanism
A well-characterised autoimmune mechanism producing a known CNS phenotype — and responding strongly to IMIG
In the Fourie & Armstrong 2024 case report, five PANS children treated with monthly IMIG showed a mean improvement score of 4.4 out of 5. All five scored above zero. This is a near-ceiling response for a case series of this type.
The significance for the ASD argument is direct: if IgG-mediated immunomodulation via the intramuscular route produces this level of clinical effect in a condition with a well-characterised autoimmune mechanism, it validates that the route and formulation work. The question for ASD is not whether IMIG can modulate the immune system — the PANS result establishes that it can, via this route, at this dose. The question is whether the ASD subpopulation with measurable immune dysregulation shares enough mechanistic overlap with PANS to respond similarly.
The cascade model predicts that they do — and that the more modest ASD response in the case report (+2.9/5) reflects the timing effect of intervening after years of established neuroinflammatory loading, rather than a fundamental mechanistic difference. The testable prediction: earlier intervention, in younger children with recently elevated biomarkers, should produce a response closer to the PANS result.
This is not a speculative extrapolation. It is a specific, falsifiable hypothesis that the Proposed IMIG for Autism Controlled Pilot Study with biomarker-stratified patient selection can directly test. The trial design — including the patient selection criteria, the biomarker panel, and the age envelope — is built around this prediction. See the Trial page for the full design rationale.
For the full evidence base — Rossignol & Frye 2021, Fourie & Armstrong 2024, and what the data collectively points toward — see the Evidence page.