Glossary

Aldosterone is an adrenal mineralcorticoid that regulates electrolyte balance and blood pressure. Levels of aldosterone typically increase in response to stress. Aldosterone plays a mechanistic role in the link between chronic stress and excessive inflammation.

Alpha-amylase is a digestive enzyme that increases in response to acute stress. It is frequently used as a salivary measure of sympathetic nervous system activity.

Anti-SARS-CoV-2 IgG - Immunoglobin G (IgG) is the most common antibody in body, representing approximately 75% of serum antibodies in human blood. After an infection, it takes weeks for levels of IgG specific to the pathogen to increase in circulation, but levels remain elevated for months to years. The presence of IgG antibodies specific to a given pathogen (e.g., the virus that causes chicken pox, etc.) suggest that a person has previously been exposed to that pathogen. Anti-SARS-CoV-2 IgG refers to IgG that specifically binds to antigenic components of the SARS-CoV-2 virus that causes COVID-19 (namely S1 domain of the spike protein).

Blood glucose level refers to the concentration of glucose in the blood. Regulation of blood glucose levels is central to metabolic health, and elevations outside of the healthy range occur in the context of metabolic disorders, like diabetes. Fasting blood glucose levels, when coupled with fasting insulin levels, can be used to measure insulin resistance. Note that serum and plasma levels of glucose are slightly higher than whole blood levels.

C-Reactive Protein (CRP) is an acute phase protein produced by the liver that can serve as a nonspecific index of bodily inflammatory activity. Note that CRP is less likely than proinflammatory cytokines to directly influence neural activity. Accordingly, it should not be used to test mechanistic relationships between inflammation and specific psychological outcomes. Because it is a nonspecific measure, CRP is generally used as an index of chronic (rather than acute) inflammatory activity. However, research suggests that that CRP levels may also increase in response to acute immunological stressors.

Cortisol is an adrenal glucocorticoid that is released when the HPA-axis has been engaged. It is frequently used as a measure of psychosocial stress. While acute stress tends to increase levels of cortisol, some research finds that chronic stress leads to blunted cortisol rhythms. Note that cortisol also influences blood sugar levels, metabolism, and immune activity. Most of the cortisol in the blood (~90%) is bound to corticosteroid-binding globulin which renders the hormone inactive. On the contrary, cortisol found in saliva is mostly free, unbound, and biologically active.

DHEA is an adrenal androgen that increases in response to stress (especially chronic stress). DHEA-S is a sulfated version of DHEA, with levels that are 100x higher than DHEA. DHEA is converted to various sex hormones in the body and plays a role in regulating aging and immune function.

DHEA is an adrenal androgen that increases in response to stress (especially chronic stress). DHEA-S is a sulfated version of DHEA, with levels that are 100x higher than DHEA. DHEA is converted to various sex hormones in the body and plays a role in regulating aging and immune function.

Estradiol is a female sex hormone. Estradiol peaks near ovulation - when women release an egg each month - and reaches peak levels when fertility is high (both across the lifespan and across the menstrual cycle). Estradiol levels may be associated with levels of female sexual desire, attunement to men, women's partner preferences, and physical attractiveness, particularly when measured within women (compared to between women). Estradiol also modulates immune function.

Ghrelin is a hormone produced primarily in the stomach. It is termed the ‘hunger hormone’ because it stimulates appetite, increases food intake, and promotes fat storage. It also stimulates the release of growth hormone. When administered to humans, ghrelin increases food intake by up to 30%; it circulates in the bloodstream and acts at the hypothalamus, an area of the brain crucial in regulating eating behavior. Ghrelin has also been shown to act on regions of the brain involved in reward processing, such as the amygdala and mesolimbic dopamine pathway.

Glucagon-like peptide 1 [GLP-1] belongs to a family of hormones called ‘incretins’ because they enhance the secretion of insulin in response to food intake. Increased levels of GLP-1 are generally detectable after 10 minutes of starting to eat and levels remain elevated in the blood for several hours after food has been consumed. GLP-1 is a satiety hormone as it plays a role in reducing appetite in response to food intake. It has been hypothesized that too little GLP-1 released after a meal may promote obesity because it could prompt individuals to continue eating even after their energy needs have been met.

Hemoglobin A1c (HbA1c) is often measured to estimate what a person’s average blood sugar levels have been over a period of months. It is frequently used to assess how well blood sugar is being controlled in patients with diabetes and can be an index of appropriate glucose regulation.

Immunoglobin G (IgG) is the most common antibody in body, representing approximately 75% of serum antibodies in human blood (although it is also found in smaller amounts in other fluids). IgG molecules are produced and released by plasma B cells. IgG binds to, tags, and neutralizes pathogens as part of the adaptive (specific) immune system. After an infection, it takes weeks for levels of IgG specific to the pathogen to increase in circulation, but levels remain elevated for months to years. The presence of IgG antibodies specific to a given pathogen (e.g., the virus that causes chicken pox, etc.) suggest that a person has been exposed to that pathogen and is likely better able to mount an immunological defense against it in the future.

Insulin is an anabolic hormone produced by the pancreas. It promotes glucose uptake and metabolism in liver, fat, and muscle cells. Thus, increases in insulin levels lead to decreases in circulating blood glucose. Absent and dysregulated insulin signaling are at the core of Type I and Type II diabetes, respectively.

Interferon gamma (IFN‐γ) is a pleiotropic cytokine that plays an important role in inducing and modulating an array of immune responses, particularly in the context of viral and intracellular bacterial infections. IFN‐γ is primarily produced by lymphocytes and promotes macrophage activation, orchestrates the activities of the innate immune system, regulates Th1/Th2 balance, and controls cellular proliferation and apoptosis. Research finds that IFN‐γ may play a role in modulating behavioral responses to stress. This analyte is eligible for multiplexing.

Interleukin 1β (IL-1β) is a proinflammatory cytokine that is produced by activated macrophages in response to immunological challenge and is a key mediator of the body’s inflammatory response. Although essential for the host response to pathogens, it can also contribute to the tissue damage that occurs in the context of excessive inflammation. Because cytokines - like IL-1β - impact nervous system activity, they can potentially serve as mechanisms linking health to behavior. In addition to increasing in response to infection, levels of this cytokine also increase in response to psychosocial stress. Levels are generally low in healthy people's blood (making them easier to capture in saliva than serum or plasma). This analyte is eligible for multiplexing.

Interleukin 10 (IL-10) is also known as cytokine synthesis inhibitory factor. IL-10 has potent anti-inflammatory properties and plays a central role in limiting host immune response to pathogens, thereby preventing damage to the host and maintaining normal tissue homeostasis. Dysregulation of IL-10 is associated with enhanced immunopathology in response to infection as well as increased risk for development of many autoimmune diseases. IL-10 also influences the nervous system and may modulate depressive and anxious behavior. This analyte is eligible for multiplexing.

Interleukin 12p70 (IL-12p70) is pleiotropic proinflammatory cytokine that plays an important role in regulating immunological function. Produced predominantly by dendritic cells, monocytes, macrophages, and T lymphocytes, IL-12p70 activates and links the activities of the innate and adaptive immune responses. IL-12p70 is an important regulator of Th1 responses, promotes the expansion and survival of activated T-cells and NK cells, and modulates the cytotoxic activity of cytotoxic T lymphocytes and NK cells. Because levels of this cytokine are typically low in the blood of healthy people, measuring this cytokine in serum or plasma may require an ultra-sensitive assay. This analyte is eligible for multiplexing.

Interleukin 13 (IL-13) is a pleiotropic protein that exerts effects similar to that of the cytokine IL-4. IL-13 is released by Th2 cells, T cells, NK cells, basophils and eosinophils. While IL-13 has anti-inflammatory properties, it is also a central mediator of allergic inflammation and regulates the production of IgE (an antibody type involved in allergy). Levels of IL-13 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay. This analyte is eligible for multiplexing.

Interleukin 17A (IL-17A) is also known as cytotoxic T-lymphocyte-associated antigen 8. IL-17A is a proinflammatory cytokine that is primarily produced by activated T cells, including TH17 cells. This cytokine regulates the activities of NF-kappaB (a protein complex that regulates cytokine production) and MAPK (a protein kinase that regulates cellular immune responses). IL-17A has been implicated in a number of chronic inflammatory conditions, such as rheumatoid arthritis and asthma. Because levels of 17A are typically low in the blood of healthy people, measuring this cytokine in serum or plasma may require an ultra-sensitive assay. This analyte is eligible for multiplexing.

Interleukin 1RA (IL-1RA) is an agent that binds to the cell surface of the interleukin-1 receptor (IL-1R), the same receptor activated by interleukin 1 (IL-1β), preventing IL-1β from sending a signal to that cell. IL-1RA is secreted by various types of cells including immune cells, epithelial cells, and adipocytes, and is a natural inhibitor of the proinflammatory effects of IL-1β. This analyte is eligible for multiplexing.

Interleukin 2 (IL-2) is also known as T-cell growth factor. IL-2 is a pleiotropic cytokine produced and released by activated T cells that plays a key role in regulating T-cell proliferation. This cytokine is also involved in the prevention of autoimmune conditions by promoting immature T cells to differentiate into T regulatory cells. IL-2 is used as a pharmaceutical drug in the treatment of certain cancers. Because levels of this cytokine are typically low in the blood of healthy people, an ultra-sensitive assay may be required to measure this cytokine in serum or plasma. This analyte is eligible for multiplexing.

Interleukin 4 (IL-4) is also known as B-cell stimulatory factor 1. IL-4 is a pleiotropic anti-inflammatory cytokine that is secreted primarily by mast cells, Th2 cells, eosinophils and basophils. Recent studies also indicate that IL-4 enhances Th2 immunity by inhibiting Th1 responses through suppression of IL-12 signaling. In addition to playing an important role in modulating the activities of the immune system, research indicates that it also plays a critical role in higher functions of the normal brain, such as memory and learning (although the precise mechanisms are not well-understood). Levels of IL-4 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay.

Interleukin 5 (IL-5) is also known as B-cell growth factor II. IL-5 is pleiotropic cytokine that is primarily produced by TH2 cells and eosinophils. It plays important roles in promoting the differentiation of B-cells into immunoglobulin-secreting cells, stimulating IgA secretion, and activating eosinophils. IL-5 is involved in the pathology of allergic diseases and is a key target for drugs developed to treat severe asthma. Levels of IL-5 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay. This analyte is eligible for multiplexing.

Interleukin 6 (IL-6) is also known as B-cell stimulatory factor 2. IL-6 is a pleiotropic cytokine with complex roles in immune function and metabolic disease. It is often used as an index of bodily inflammatory activity, as it is a potent inducer of the acute phase response. However, it should be noted that IL-6 also has anti-inflammatory properties, which may make it an unreliable index of inflammation on its own. IL-6 has been shown to influence the nervous system and may mediate links between immune activation and behavior. In addition to increasing in response to infection, levels of this cytokine also increase in response to psychosocial stress. Levels of IL-6 are typically very low in saliva, which makes this cytokine more difficult to measure in saliva than serum or plasma. This analyte is eligible for multiplexing.

Interleukin 7 (IL-7) is a pleiotropic protein that stimulates lymphocyte maturation and proliferation. It is involved in several additional facets of immunity, including cell to cell communication and regulation of the humoral immune response. IL-7 has been implicated in a number of different disorders, such as multiple sclerosis and cancer. This analyte is eligible for multiplexing.

Interleukin 8 (IL-8) is also known as granulocyte chemotactic protein 1. IL-8 is a pleiotropic proinflammatory chemokine that plays a key role in the recruitment of neutrophils and other immune cells to the site of infection. As such, many studies use levels of IL-8 as an early-phase biomarker. In addition to being released by macrophages, IL-8 is also released by epithelial cells, airway smooth muscle cells, and endothelial cells. Levels of IL-8 have also been found to be elevated in the cerebrospinal fluid of patients with traumatic brain injury. This analyte is eligible for multiplexing.

Leptin is a hormone produced primarily by adipocytes (or fat cells) in the body that plays a role in bodily energy homeostasis. While leptin shows some ability to acutely reduce hunger following a meal, it primarily acts to alter food intake and control energy expenditure over the long term. Leptin has its most profound effect when weight is lost and levels of the hormone fall, which increases hunger and appetite. Diminished tissue sensitivity to leptin (i.e., leptin resistance) is involved in the etiology of obesity and other metabolic disorders.

Luteinizing hormone (LH) is a hormone released from the pituitary gland that plays a key role in coordinating both women's and men's reproductive function. In women, an acute elevation in LH ("LH surge") initiates ovulation. In men, LH stimulates testosterone production in the testes. LH is typically measured in studies to determine women's ovulatory status. In clinical settings, LH is measured alongside sex hormones (e.g., testosterone, estradiol) in the diagnosis of reproductive disorders.

Progesterone is a female sex hormone that is released in large quantitates after ovulation, in the luteal phase of the menstrual cycle. It plays a critical role in pregnancy and is known to have anxiolytic effects. Progesterone also modulates immune function both within and outside the context of pregnancy.

Secretory Immunoglobin A (SIgA) is the most common antibody found in mucosal membranes where it acts as a first line of defense against pathogens that invade bodily secretions. Like other antibodies, SIgA is produced and released by B cells. Levels of SIgA are often used as measure of mucosal immune activation in response to psychosocial stress.

Sex Hormone Binding Globulin (SHBG) is a protein primarily produced in the liver that binds to the sex hormones testosterone (an androgen), dihydrotestosterone (DHT) (an androgen), and estradiol (an estrogen) in the blood, rendering them biologically inactive. Changes in SHBG levels can affect the amount of these hormones that is available to activate hormone receptors in tissues throughout the body.

Testosterone is the primary male sex hormone. It also plays an important role in motivating competitive and sexual behaviors in both men and women, and it increases in response to sexual stimuli and competitive victories. Total T measures total levels of testosterone, whereas free T captures only unbound, biologically active levels of T. Either total T or free T can be measured in serum and plasma, but only free T can be measured in saliva. While testosterone is generally considered immunosuppressive, research finds that it has complex effects on different types of immune function.

Testosterone is the primary male sex hormone. It also plays an important role in motivating competitive and sexual behaviors in both men and women, and it increases in response to sexual stimuli and competitive victories. Total T measures total levels of testosterone, whereas free T captures only unbound, biologically active levels of T. Either total T or free T can be measured in serum and plasma, but only free T can be measured in saliva. While testosterone is generally considered immunosuppressive, research finds that it has complex effects on different types of immune function.

Tumor necrosis factor α (TNF-α) is a pleiotropic, proinflammatory mediator that is involved in a wide range of inflammatory, infectious, autoimmune and malignant conditions. This cytokine has been implicated in a variety of diseases, including autoimmune diseases, insulin resistance, and cancer. TNF-α has been shown to impact nervous system activity and may play a mechanistic role in the relationship between inflammation and behavior. In addition to increasing in response to infection, levels of this cytokine also increase in response to psychosocial stress. This analyte is eligible for multiplexing.

Interleukin 12p70 (IL-12p70) is pleiotropic proinflammatory cytokine that plays an important role in regulating immunological function. Produced predominantly by dendritic cells, monocytes, macrophages, and T lymphocytes, IL-12p70 activates and links the activities of the innate and adaptive immune responses. IL-12p70 is an important regulator of Th1 responses, promotes the expansion and survival of activated T-cells and NK cells, and modulates the cytotoxic activity of cytotoxic T lymphocytes and NK cells. Because levels of this cytokine are typically low in the blood of healthy people, measuring this cytokine in serum or plasma may require an ultra-sensitive assay. Ultra-sensitive versions of assays CANNOT be multiplexed.

Interleukin 13 (IL-13) is a pleiotropic protein that exerts effects similar to that of the cytokine IL-4. IL-13 is released by Th2 cells, T cells, NK cells, basophils and eosinophils. While IL-13 has anti-inflammatory properties, it is also a central mediator of allergic inflammation and regulates the production of IgE (an antibody type involved in allergy). Levels of IL-13 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay. Ultra-sensitive versions of assays CANNOT be multiplexed.

Interleukin 17A (IL-17A) is also known as cytotoxic T-lymphocyte-associated antigen 8. IL-17A is a proinflammatory cytokine that is primarily produced by activated T cells, including TH17 cells. This cytokine regulates the activities of NF-kappaB (a protein complex that regulates cytokine production) and MAPK (a protein kinase that regulates cellular immune responses). IL-17A has been implicated in a number of chronic inflammatory conditions, such as rheumatoid arthritis and asthma. Because levels of 17A are typically low in the blood of healthy people, measuring this cytokine in serum or plasma may require an ultra-sensitive assay. Ultra-sensitive versions of assays CANNOT be multiplexed.

Interleukin 2 (IL-2) is also known as T-cell growth factor. IL-2 is a pleiotropic cytokine produced and released by activated T cells that plays a key role in regulating T-cell proliferation. This cytokine is also involved in the prevention of autoimmune conditions by promoting immature T cells to differentiate into T regulatory cells. IL-2 is used as a pharmaceutical drug in the treatment of certain cancers. Because levels of this cytokine are typically low in the blood of healthy people, an ultra-sensitive assay may be required to measure this cytokine in serum or plasma. Ultra-sensitive versions of assays CANNOT be multiplexed.

Interleukin 4 (IL-4) is also known as B-cell stimulatory factor 1. IL-4 is a pleiotropic anti-inflammatory cytokine that is secreted primarily by mast cells, Th2 cells, eosinophils and basophils. Recent studies also indicate that IL-4 enhances Th2 immunity by inhibiting Th1 responses through suppression of IL-12 signaling. In addition to playing an important role in modulating the activities of the immune system, research indicates that it also plays a critical role in higher functions of the normal brain, such as memory and learning (although the precise mechanisms are not well-understood). Levels of IL-4 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay. Ultra-sensitive versions of assays CANNOT be multiplexed.

Interleukin 5 (IL-5) is also known as B-cell growth factor II. IL-5 is pleiotropic cytokine that is primarily produced by TH2 cells and eosinophils. It plays important roles in promoting the differentiation of B-cells into immunoglobulin-secreting cells, stimulating IgA secretion, and activating eosinophils. IL-5 is involved in the pathology of allergic diseases and is a key target for drugs developed to treat severe asthma. Levels of IL-5 are typically low in the blood of healthy people, so measuring this cytokine in serum or plasma may require an ultra-sensitive assay. Ultra-sensitive versions of assays CANNOT be multiplexed.