The Interconnectedness of the Brain, Behavior, and Immunology and the Difficult to Overstate Flaccidity of The Correlation Is Not Causation Argument

Posted by: passionlessdrone on: May 12, 2011

• In: Autism | Beautiful Complexity | Biological Plausibility | Brain | Gross Over Simplification | IL-6 | Immunology | Inflammation | Some Jerk On The Internet | Tnf-Alpha | Toll Like Receptors | Uncategorized | Vaccines! | Willing Disbelief
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Hello friends –

I’ve gotten into a lot of discussions online about the vaccines and autism; generally with very poor, if not nonexistent, evidence of having changed any opinions, but relatively strong evidence ( p >  .001) that persisting in making my arguments can get you called ‘an antivaccine loon’, ‘idiot’, someone who engages in ‘Gish Gallop’, or the worst insult I’ve received so far, ‘anti-science’.   While I am really torn on the vaccine issue, I am certain that both peripheries of this debate are at least somewhat wrong in the conclusions that they’ve drawn from the available evidence.  I do believe that lots of parents have witnessed a very real change in their children post vaccination, and I also don’t believe for a single second that vaccines are the cause of an epidemic of autism.  It’s a mess and I’ve been poking around the Internet almost five years into journey autism and from my eyes, it hasn’t improved any in the past half decade.  This is very sad.

That being said, while I do think we need to have a rational and dispassionate discussion about what our existing vaccine studies can and cannot tell us about autism, I’m really concerned about the fact that the vaccine wars seem to have inoculated otherwise intelligent people from any semblance of intellectual curiosity regarding the immunological findings in the autism realm.  That’s a problem, because there are lots of things other than vaccines that can modify the immune response, various environmental agents and cultural changes that are relatively new, and ignoring immunological findings in autism because they happen to intersect with the function of vaccination is a huge, massive, supernova sized disservice to what history will view us poorly on, refusing to perform honest evaluation due to fear and the comfort of willful ignorance.

Here, in this post, I will make the case that this lack of curiosity on immunological findings in autism is either born of a lack of understanding on how much we know about the ties between the immune system and the brain, or alternatively, originates from a deep seated desire to avoid honest interactions.  This isn’t to make the case that vaccines can cause autism, or even that the immunological disturbances observed in autism are causative, but rather that an obstinate refusal to consider these as possibilities is the sign of someone who cannot, or will not accept, the biological plausibility of immunologically driven behaviors despite a constellation of evidence.

One of the things that jumps out to me why the autism population might be a subgroup of the population susceptible to changes as a result of immune dysfunction (and thus, potentially adversely affected as a result of vaccination), is the sheer volume of evidence we now have available to us indicating an altered immune response, and indeed, an ongoing state of inflammation within the brain in the autism population, and most strikingly, repeated observations of a correlation between the degree of immune dysregulation as a propensity of an inflammatory state, and the severity of autism behaviors.  Again and again we’ve seen that as markers indicative of an inflammatory state increase, so too, do severity of autism behaviors.  Not only that, but there are instances wherein the decrease of components known to regulate the immune response decrease, autistic behaviors are more severe.  Subtle shifts in either the start or the resolution of the immune response seems to affect autistic behavior severity in the same way.   I know coincidences happen all the time, but that doesn’t mean that everything is a coincidence. 

We also have a large number of studies that tell us that in vitro, similar levels of stimulation with a variety of agents cause exaggerated or dysregulated production of immune markers in the autism population.   

A large percentage of the time that I mention these findings, usually within discussions with an origin in vaccination, someone decides to educate me on one of the most rudimentary scientific axioms:

Correlation does not equal causation.

It must be stated, the above statement is absolutely true.  Unfortunately for the people for whom this accurate, but simplistic catchphrase comprises the entirety of their argument, it completely ignores a wealth of research that tells us in very unambiguous terms that there is incontrovertible evidence that crosstalk between the immune system and central nervous system can modify behavior. The research indicating a relationship between immune dysregulation and autism does not exist in a vacuum, but rather, is only a tiny fragment of evidence, mostly accumulated within the last few years, that tells us that the paradigm of the past decades, that of the brain as a immune privileged organ without communication to the immune system, is as antiquated as refrigerator moms and a one in ten thousand prevalence. 

From a common sense, why didn’t I think of that standpoint, the best example of the interaction between the brain and the immune response is the old standard, just plain old getting sick.  You live in the dirty world, you pick up a pathogen, you get sick, and suddenly you get lethargic and you start to run a fever.  But is it the pathogen itself that is actually making you feel like staying in bed all day? 

What is being learned is that it is not necessarily the microbial invader that is causing you to get tired and feel sore, but rather, that your decreased energy levels are centrally mediated through your brain, and the triggers for your brain to start a fever include molecules our bodies use for a wide range of communications, including immune based messaging, cytokines.  Some of the most common cytokines in the research to follow include IL-6, IL-1B, and TNF-Alpha; so called ‘pro-inflammatory’ cytokines.  Researchers have been plugging away at just how the immune response is capable of modifying behaviors, i.e., inducing, sickness behavior for a while now, at least in terms of autism research.  From 1998, we have Molecular basis of sickness behavior:

Peripheral and central injections of lipopolysaccharide (LPS), a cytokine inducer, and recombinant proinflammatory cytokines such as interleukin-1 beta (IL-1 beta) induce sickness behavior in the form of reduced food intake and decreased social activities. Mechanisms of the behavioral effects of cytokines have been the subject of much investigation during the last 3 years. At the behavioral level, the profound depressing effects of cytokines on behavior are the expression of a highly organized motivational state. At the molecular level, sickness behavior is mediated by an inducible brain cytokine compartment that is activated by peripheral cytokines via neural afferent pathways. Centrally produced cytokines act on brain cytokine receptors that are similar to those characterized on peripheral immune and nonimmune cells, as demonstrated by pharmacologic experiments using cytokine receptor antagonists, neutralizing antibodies to specific subtypes of cytokine receptors, and gene targeting techniques. Evidence exists that different components of sickness behavior are mediated by different cytokines and that the relative importance of these cytokines is not the same in the peripheral and central cytokine compartments.

The first sentence in this abstract references a practice that is extremely common in studying the immune system, intentionally invoking a robust immune response by exposing either animals, or cells in vitro, to the components that comprise the cell wall of certain types of bacteria; lipopolysaccharide, or LPS.  LPS could be considered a sort of bacterial fingerprint, a pattern that our immune systems, and the immune system of almost everything, has evolved to recognize, and correspondingly initiates an immune response. 

Because this is a conversation that frequently has an origin in vaccination, essentially the act of faking an infection, it is salient to remember that the animals or cell cultures aren’t really getting sick when exposed to LPS; there is no pathology associated with whatever type of bacteria might be housed within a cell membrane containing LPS.  Usually, when the body is exposed to a gram negative bacteria, and the consequent LPS exposure, there are also effects of the bacteria that interact with the organism, but by only incorporating the alert signal for a bacterial invader, we can gain insight into the effect of the immune response itself; there isn’t anything else to cause any changes.   This means that similarly to LPS administration, straight administration of these pro-inflammatory cytokines are similar to the result of getting sick with a pathogen, at least as far as the immune response is concerned. 

In the above instance, administration of LPS, or simply cytokines, had been shown to be capable of causing reduced food intake and ‘decreased social activities’. 

Later in 1998, Central administration of rat IL-6 induces HPA activation and fever but not sickness behavior in rats  (full version), was published wherein the authors report that central administration (i.e., directly into the CNS), of cytokines in isolation (IL-6) or in combination (IL-6 + IL-1B) were capable of inducing altered HPA activation, fevers, and sickness behaviors.  Effects of peripheral administration of recombinant human interleukin-1 beta on feeding behavior of the rat was published a few years later, and observed that peripheral administration (i.e., not the CNS) of IL-1B could affect how much a rat ate, with sucrose ingestion being consistently altered during periods of sickness. 

Jumping ahead a few years, a review paper Expression and regulation of interleukin-1 receptors in the brain. Role in cytokines-induced sickness behavior reviewed how cytokines participate in sickness behavior, Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior examined the interactions of IL-6 and leptin in sickness behavior, and Behavioral and physiological effects of a single injection of rat interferon-alpha on male Sprague-Dawley rats: a long-term evaluation reported “these data suggest that a single IFN-alpha exposure may elicit long-term behavioral disruptions”. 

Much more recently, Sickness-related odor communication signals as determinants of social behavior in rat: a role for inflammatory processes more elegantly found that behavior was modified by LPS exposure, and that this effect was neutralized by concurrent administration of the anti-inflammatory cytokine, IL-10.  Similarly, Inhibition of peripheral TNF can block the malaise associated with CNS inflammatory diseases observed another distinct means by which interfering with the immune response could attenuate the effect of faux sickness, in part, concluding, “Thus behavioral changes induced by CNS lesions may result from peripheral expression of cytokines that can be targeted with drugs which do not need to cross the blood-brain barrier to be efficacious.”  In other words, what is happening in the periphery, outside of the protective boundaries of the blood brain barrier, can none the less manipulate behaviors that are controlled by the brain. 

There are tons, tons more studies like this, but the point should be clear by now; it is accepted that you can achieve some of the same behaviors the come alongside illness, such as fever and lethargy, without the presence of an actual bacteria or virus; all you need is for your brain to think that you are sick. 

While it must be acknowledged that the behavioral disturbances observed in autism are a lot different than feeling the need to watch TV all day, these types of studies were among the first clues that the traditional view of the CNS as a separate entity within the gated community of the blood brain barrier needed revision.   

Measuring how much sugar water a rat drank is great stuff, but the reality is that we have conservatively a gazillion studies telling us that disorders that manifest behaviorally have strong, strong ties to the immune system; and once we begin to understand the vast scope of these findings, the utter frailty of “correlation does not equal causation” becomes painfully clear to the intellectually honest observer. 

The big problem I found myself with in crafting this posting was that the sheer volume of studies available really makes a complete illustration of the literature impossible; I started looking and pubmed nearly puked trying to return to me a listing of all of the things I wanted to summarize.  So here is some of the best of the best; to keep things interesting, I thought I’d only include findings from 2007 or later as a mechanism to show just how nascent our understanding of the connections between the brain and the immune system really are. 

Initially, we can start with a condition that nearly everyone agrees is diagnosed based on behavior, depression.  It turns out, the number of findings establishing a link between immune system markers and depression is wide and deep.   

Here’s a great one, Elevated macrophage migration inhibitory factor (MIF) is associated with depressive symptoms, blunted cortisol reactivity to acute stress, and lowered morning cortisol, which reports, that MIF can modify HPA axis function and is tied to depression; a particularly compelling finding considering well documented alterations in HPA axis metabolites in autism, and the fact that increased MIF has also been found in the autism population, and as levels increased, so too did autism severity. 

Here is part of the abstract for Inflammation and Its Discontents: The Role of Cytokines in the Pathophysiology of Major Depression (full paper)

Patients with major depression have been found to exhibit increased peripheral blood inflammatory biomarkers, including inflammatory cytokines, which have been shown to access the brain and interact with virtually every pathophysiologic domain known to be involved in depression, including neurotransmitter metabolism, neuroendocrine function, and neural plasticity. Indeed, activation of inflammatory pathways within the brain is believed to contribute to a confluence of decreased neurotrophic support and altered glutamate release/reuptake, as well as oxidative stress, leading to excitotoxicity and loss of glial elements, consistent with neuropathologic findings that characterize depressive disorders.

Somewhere along the way, researchers discovered that some anti-depressants can exert anti-inflammatory effects, for examples of these findings we could look to Fluoxetine and citalopram exhibit potent antiinflammatory activity in human and murine models of rheumatoid arthritis and inhibit toll-like receptors, or Plasma cytokine profiles in depressed patients who fail to respond to selective serotonin reuptake inhibitor therapy, which concludes in part, “Suppression of proinflammatory cytokines does not occur in depressed patients who fail to respond to SSRIs and is necessary for clinical recovery”. 

In Investigating the inflammatory phenotype of major depression: focus on cytokines and polyunsaturated fatty acids, the authors report that, “The findings of this study provide further support for the view that major depression is associated with a pro-inflammatory phenotype which at least partially persists when patients become normothymic.”  A nice review of the evidence of immunological participation in depression can be found in The concept of depression as a dysfunction of the immune system (full paper).

Moving forward, we can look to schizophrenia, we have similar findings, including Serum levels of IL-6, IL-10 and TNF-a in patients with bipolar disorder and schizophrenia: differences in pro- and anti-inflammatory balance, which observed an imbalanced baseline cytokine profile in the schizophrenic group; findings very similar in form with An activated set point of T-cell and monocyte inflammatory networks in recent-onset schizophrenia patients involves both pro- and anti-inflammatory forces. Similarly, the findings from Dysregulation of chemo-cytokine production in schizophrenic patients versus healthy controls, (full paper) which states, in part:

Growing evidence suggests that specific cytokines and chemokines play a role in signalling the brain to produce neurochemical, neuroendocrine, neuroimmune and behavioural changes. A relationship between inflammation and schizophrenia was supported by abnormal cytokines production, abnormal concentrations of cytokines and cytokine receptors in the blood and cerebrospinal fluid in schizophrenia

Their findings include differentially increased and decreased production of chemokines and cytokines as a result of LPS stimulations in the case group.  Of particular note, a similarly dysregulated immune profile of cytokine and chemokine generation has been found in the autism population in several studies.  

We also have several trials of immunomodulatory drugs in the schizophrenic arena that further implicate the immune system in pathology, including Adjuvant aspirin therapy reduces symptoms of schizophrenia spectrum disorders: results from a randomized, double-blind, placebo-controlled trial, a ‘gold standard’ trial which found that, “Aspirin given as adjuvant therapy to regular antipsychotic treatment reduces the symptoms of schizophrenia spectrum disorders. The reduction is more pronounced in those with the more altered immune function. Inflammation may constitute a potential new target for antipsychotic drug development”.  A similar clinical trial, Celecoxib as adjunctive therapy in schizophrenia: a double-blind, randomized and placebo-controlled trial , another gold standard trial, which also had findings in the same vein, “Although both protocols significantly decreased the score of the positive, negative and general psychopathological symptoms over the trial period, the combination of risperidone and celecoxib showed a significant superiority over risperidone alone in the treatment of positive symptoms, general psychopathology symptoms as well as PANSS total scores.” [Celecoxib is a cox-2 inhibitor; i.e., anti-inflammatory, i.e., immunomodulatory]

What about bi-polar disorder?  More of the same, including, The activation of monocyte and T cell networks in patients with bipolar disorder, or Elevation of cerebrospinal fluid interleukin-1ß in bipolar disorder, which reports, in part, “Our findings show an altered brain cytokine profile associated with the manifestation of recent manic/hypomanic episodes in patients with bipolar disorder. Although the causality remains to be established, these findings may suggest a pathophysiological role for IL-1ß in bipolar disorder.”. These studies were published in April and March, 2011, respectively. 

Brain tissue from persons with bi-polar disorder also showed increased levels of excitotoxicity and neuroinflammation in Increased excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from bipolar disorder patients (full version), and authors report differential cytokine profiles depending on state of mania, depression, or remission in Comparison of cytokine levels in depressed, manic and euthymic patients with bipolar disorder.

Another disorder based solely around behavior, Tourette syndrome, has increasingly unsurprising findings.  Polymorphisms of interleukin 1 gene IL1RN are associated with Tourette syndrome reports “The odds ratio for developing Tourette syndrome in individuals with the IL1RN( *)1 allele, compared with IL1RN( *)2, was 7.65.” (!!!) , and Elevated expression of MCP-1, IL-2 and PTPR-N in basal ganglia of Tourette syndrome cases is yet another example of observations of CNS based immune participation in a disorder that is diagnosed by behavior.

There are also some reviews that perform a cross talk of sorts between disorders; i.e., The mononuclear phagocyte system and its cytokine inflammatory networks in schizophrenia and bipolar disorder, or Immune system to brain signaling: Neuropsychopharmacological implications, published in May 2011, which has this abstract:

There has been an explosion in our knowledge of the pathways and mechanisms by which the immune system can influence the brain and behavior. In the context of inflammation, pro-inflammatory cytokines can access the central nervous system and interact with a cytokine network in the brain to influence virtually every aspect of brain function relevant to behavior including neurotransmitter metabolism, neuroendocrine function, synaptic plasticity, and neurocircuits that regulate mood, motor activity, motivation, anxiety and alarm. Behavioral consequences of these effects of the immune system on the brain include depression, anxiety, fatigue, psychomotor slowing, anorexia, cognitive dysfunction and sleep impairment; symptoms that overlap with those which characterize neuropsychiatric disorders, especially depression. Pathways that appear to be especially important in immune system effects on the brain include the cytokine signaling molecules, p38 mitogen-activated protein kinase and nuclear factor kappa B; indoleamine 2,3 dioxygenase and its downstream metabolites, kynurenine, quinolinic acid and kynurenic acid; the neurotransmitters, serotonin, dopamine and glutamate; and neurocircuits involving the basal ganglia and anterior cingulate cortex. A series of vulnerability factors including aging and obesity as well as chronic stress also appears to interact with immune to brain signaling to exacerbate immunologic contributions to neuropsychiatric disease. The elucidation of the mechanisms by which the immune system influences behavior yields a host of targets for potential therapeutic development as well as informing strategies for the prevention of neuropsychiatric disease in at risk populations.

All of the conditions above, depression, schizophrenia, bi-polar, and tourettes are diagnosed behaviorally; it is only in the last few years that the medical dimension of these disorders were even understood to exist.   None of the studies that I referenced above are more than five years old; the idea that behavioral disorders were so closely entangled with the immune system is very, very new.  It should be noted that I intentionally left out disorders that also have reams of evidence of immune participation, but which are more degenerative in nature; i.e., Alzheimer’s, ALS, Parkinson’s.  When discussing autism, I also left out studies involving aberrant presence of auto-antibodies, of which there are many.

One of the things that I have learned in trying to refine my thought processes during my time on the Internet is that rarely does a single study tell us much about a condition; but the converse also holds true, if we have many studies with different methodologies or measurement end points, but they all reach similar conclusions, then the likely-hood that the findings are accurate is much, much greater.  All of the studies I have listed above tell us something similar; that the immune system is clearly, unmistakably playing a part in a lot of conditions classically considered neurological and diagnosed behaviorally.  It isn’t enough to nitpick flaws in a single one of the studies in order for ‘correlation does not equal causation’ to make meaningful headway into the implications of these studies; instead, all of the studies above, and lots more, have to be wrong in the same way if we would like to return to a place where we can keep our heads in the sand, hoping for coincidences and bleating out catchphrases in the face of clinical findings.  That isn’t going to happen.  Given this reality, we should not and cannot ignore the growing evidence of immune abnormalities in the autism population, no matter how inconvenient following that trail of evidence might become. 

-pD

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Tags: Autism, Biological Plausibility, Cytokines, Fascinating, Immune, Immune System, Inconvenient Findings, Inflammation, Innate Immune Response, Interconnectedness, Mr. Rat, Neuroimmunology, Vaccines!