kynurenine pathway and plays a major role in immunoregulation, was shown in
animal models. Furthermore, pharmacological or genetic blockade of IDO
activation abrogated depression-like behavior in mice (Dantzer 2018).
Collectively, these investigations on the role of neuroimmune interactions in
psychiatric disorders have led to the emergingfield of immunopsychiatry
(Pariante 2015). This domain has its origins in neuroimmunology and psycho-
neuroimmunology but focuses on the influence of immune mechanisms on
behavior rather than the other way around.
If confirmed by future results, research on the role of the immune system in
neurological and psychiatric diseases could have interesting and innovative
therapeutic consequences. It has the potential to expand traditional approaches
that see such diseases as purely mental and/or neurological, especially if future
investigations confirm that some of these diseases can be managed via targeting
of the immune system (among other components). This includes major depres-
sive disorder (Miller and Raison 2016; Bullmore 2018), bipolar disorder,
schizophrenia, and several others (Miller and Buckley 2017). The possibility
to treat neurodegenerative disorders via immunotherapies also is under intense
investigation (Weiner and Frenkel 2006).
Interestingly, an immunological approach could lead to redefined nomen-
clatures of psychiatric disorders and treatments. Diagnosis for psychiatric
disorders is currently based on descriptive nomenclature because of a lack
of clearly defined causal mechanisms. Yet some immunological mechan-
isms are common to psychiatric disorders belonging to different categories,
hence the suggestion to develop alternative nomenclatures based on immu-
nological characteristics as well as associated environmental factors
(Leboyer et al. 2016).
Reciprocally, some diseases traditionally classified as immune may be tar-
geted by acting on the nervous system. For example, in a recent clinical study,
electrical vagus nerve stimulation was successfully used to improve symptoms
in rheumatoid arthritis, a chronic inflammatory and autoimmune disease
(Koopman et al. 2016). Further investigations are needed, but some specialists
consider that bioelectronic devices can be used to modulate neural circuitries,
constituting a complement to drug treatment, especially in immune diseases
(Chavan et al. 2017)
Thefield of immunotherapy-based approaches to neurological and psychia-
tric diseases is still in its infancy. Yet if successful, it could contribute to
closing the gap between psychiatry and the rest of medicine, and it could lead
to a radical change in the way we traditionally conceive mental health
problems.
Philosophy of Immunology 53