Felix Faustus@FelixFaustus
A Bayesian Framing of the Immune-Complex Geometry Hypothesis
This is not a claim.
It is a mechanistic hypothesis with testable predictions.
Start with well-accepted premises:
Complement efficiently clears small, soluble immune complexes
Large or persistent immune complexes are more likely to deposit in microvasculature
Complement activation produces C3a, C5a, and MAC, which influence endothelial function
Microvascular dysfunction can produce subtle, diffuse physiological effects
None of these premises are controversial.
The question is whether antigen geometry and persistence could shift systems from regime (1) to regime (2).
The Geometry Hypothesis
If antigen exposure is:
• Transient
• Low density
• Fragmented
Then immune complexes tend to remain:
• Small
• Soluble
• Efficiently cleared
But if antigen exposure is:
• Persistent
• Repeating
• High-density
Then antibodies may bind along extended structures, forming:
• Larger immune complexes
• Clustered Fc regions
• Strong complement activation
However, strong activation does not necessarily imply efficient clearance.
Large immune complexes are:
• Harder to transport
• Harder to phagocytose
• More likely to interact with endothelium
• More likely to deposit in microvasculature
This is consistent with known immune-complex disease dynamics.
Why Microvasculature Matters
Microvascular beds are particularly sensitive because they:
• Have high surface area
• Experience slow or turbulent flow
• Are vulnerable to immune-complex deposition
Common targets in immune-complex disease include:
• Kidneys
• Skin
• Joints
• Small vessels
Two additional biologically plausible sites:
Brain microvasculature
Heart microvasculature
Brain
Large immune complexes do not typically cross the blood-brain barrier.
However, they do not need to cross it to influence it.
Immune-complex interaction with brain microvasculature could:
• Activate complement locally
• Trigger endothelial signaling
• Alter permeability dynamics
This does not imply BBB breakdown.
It implies potential modulation of barrier behavior, which could produce:
• Subtle
• Conditional
• Diffuse effects
Heart
The heart may be more directly exposed.
Unlike the brain, the heart lacks a comparable barrier.
It has:
• Dense microvasculature
• High metabolic demand
• Sensitivity to perfusion changes
Even small microvascular disturbances can produce:
• Transient perfusion effects
• Electrical sensitivity
• Functional variability
Cardiology already recognizes this class of phenomena:
Coronary microvascular dysfunction
Normal large arteries
Small-vessel dysfunction
Bayesian Interpretation
This hypothesis predicts:
Not catastrophic effects
Not universal harm
Not large signals
But:
Subtle
Conditional
Subgroup-dependent
Long-tail signals
Which are precisely the kinds of signals that:
• Appear intermittently
• Disappear in aggregates
• Are difficult to detect with standard epidemiology
Testable Predictions
If this model is correct, we might expect:
• Complement activation markers elevated in subsets
• Evidence of immune-complex formation in circulation
• Microvascular function differences in subgroups
• Heterogeneous outcomes rather than uniform effects
Falsifiability
This model weakens if:
• No evidence of persistent immune complexes
• No complement activation differences
• No microvascular signatures
• No subgroup-specific signals
Bayesian Bottom Line
This is not an argument from certainty.
It is a shift in generative model:
From:
Uniform exposure
Uniform clearance
Uniform outcomes
To:
Geometry-dependent exposure
Conditional clearance
Subgroup-dependent outcomes
The system doesn’t need to fail.
The regime just needs to shift.
And small regime shifts often produce long-tail signals rather than headline effects.