Innate immunity lays the foundation of the immune response and provides the first line of defense against invading pathogens. Toll-like Receptors (TLRs) are an essential aspect of this response, think of them as security guards on the outside of a cell. TLRs belong to a class of receptors which recognize unique, yet general, patterns on bacteria, viruses, or even fungi, making them members of the pathogen-recognition receptor (PRR) group. TLRs generally reside on leukocytes, mostly monocytes, dendritic cells (DCs), and neutrophils. When a pathogen binds to the receptor an intracellular signaling cascade is initiated which leads to the activation of Nf-kB, a pro-inflammatory transcription factor. Simply put, NF-kB leads to the production of cytokines, immune messengers, which can affect other immune cells and promote inflammation. The inflammatory response is characterized by localized swelling caused by vasodilation, an increase in diameter of the blood vessels. This response allows more leukocytes to travel to the area of invasion to remove the pathogen.
When asked to imagine the immune response the first thing which comes to the mind of most is the illness, usually a cold, virus, or something more severe, such as HIV. However, recent research has linked TLR deregulation to two psychiatric illnesses, schizophrenia and bipolar disorder. These are novel, intriguing directions for immunological research. Schizophrenia affects approximately 1% of the population and is characterized by positive symptoms, such as hallucinations and delusions, and negative symptoms, namely social withdrawal and lack of an emotional response. There’s no clear cut factor which causes schizophrenia but there are several genetic factors and prenatal effects. For example, there is increasing evidence that bacterial and viral infections which may occur in utero may have lasting effects on the developing fetus. Any sort of maternal immune response may lead to the production of cytokines in the mother which may cross the placenta and even the infant’s blood-brain barrier, leading to neurodevelopmental problems which may present as Schizophrenia. On the other hand, bipolar disorder affects roughly 2% of the population and is characterized by drastic mood swings. Previous research in both disorders has revealed heightened cytokine levels in both.
