CB2 Receptor

A peripheral, immune receptor in vitro

Munro, Thomas and Abu-Shaar cloned CB2 in 1993 from HL-60 promyelocytic leukaemia cells and found a receptor with clear homology to CB1 but a different distribution: abundant in spleen and in cells of the immune system, absent or minimal in brain by the methods then available. The IUPHAR classification in 2002 fixed the pairing. Expression is highest in B lymphocytes and natural killer cells, with monocytes, macrophages and T cells also carrying it, and the functional consequences run through cytokine release, chemotaxis and antigen presentation rather than through synaptic transmission. Non-immune peripheral expression has since been documented in bone, liver, gut and skin, though the mapping of those roles is less complete than the immune picture and should be treated as less settled.

Sources: Munro S 1993 · Howlett AC 2002

Microglia, and CB2 in the brain after all animal

The original "peripheral receptor" label needed qualifying. Cabral and colleagues reviewed the evidence that CB2 is present in the central nervous system on microglia, the resident immune cells of the brain, and that expression is strongly dependent on activation state — low in resting microglia, markedly upregulated in the primed and responsive states seen in injury, infection and neuroinflammation. That makes CB2 a conditional central target: it is not meaningfully there in a quiet brain and is there in an inflamed one. It also explains how a non-psychoactive CB2 agonist can have central anti-inflammatory effects without touching neuronal signalling, and why CB2 appears repeatedly in neuroinflammation and neurodegeneration work.

Sources: Cabral GA 2008

Why CB2 agonism is anti-inflammatory without psychoactivity animal

The psychoactive effects of cannabinoids are a consequence of CB1 on neurons in cortex, hippocampus, basal ganglia and cerebellum. CB2 is not on those neurons in any quantity. An agonist selective for CB2 therefore engages immune and glial signalling and leaves the neuronal circuits that produce intoxication alone. Gertsch and colleagues demonstrated the point directly with β-caryophyllene: it activated CB2, attenuated inflammatory responses in mice, and the anti-inflammatory effect was abolished in CB2-knockout animals, while the compound produced no CB1-type behavioural effects. That is the cleanest available separation of the two arms of cannabinoid pharmacology, and it is the reason CB2 is the target of choice for anti-inflammatory development, and for product work that needs cannabinoid-system engagement without an intoxicant.

Sources: Gertsch J 2008 · Munro S 1993 · Cabral GA 2008

β-caryophyllene: a dietary cannabinoid contested animal

β-caryophyllene is a bicyclic sesquiterpene present in the essential oils of black pepper, cloves, hops, rosemary, oregano, copaiba and cannabis. Gertsch and colleagues reported in 2008 that it binds and activates CB2 selectively, with no appreciable CB1 activity, and titled the paper accordingly: a dietary cannabinoid. Three properties make it unusual among terpenes. It is a functional selective agonist at a cannabinoid receptor rather than a modulator of one, which is more than can be said for the terpenes in the entourage debate. It is orally bioavailable, where many monoterpenes are not. And it holds FDA generally-recognised-as-safe status as a flavouring, which makes it usable in food and cosmetic formats without a novel-ingredient problem. In black pepper essential oil it is a major constituent; reported ranges vary widely with origin, cultivar and distillation, and the operator corpus records a 7 to 35 percent band for Piper nigrum essential oil, which is consistent with the spread in the published composition literature.

• Selective CB2 agonist, negligible CB1 activity — no intoxication.
• Orally bioavailable sesquiterpene, unlike much of the monoterpene fraction.
• GRAS as a flavouring, which is a regulatory advantage as much as a pharmacological one.
• Occurs across many culinary botanicals, so it is a shared mechanism between preparations that otherwise have nothing in common.

Contested — caveat. Essential-oil composition percentages are highly variable by cultivar, geography, plant part and distillation method; a single reported range should not be treated as a specification. The 7 to 35 percent figure for black pepper essential oil is carried from the operator corpus and is consistent with, but not a quotation from, the published composition literature.

Sources: Gertsch J 2008 · Milenković A 2024 · Van Kush Family Research Institute 2026*

CB2 outside the immune system: bone, liver, gut contested animal

Ofek and colleagues reported in 2006 that CB2 is expressed in osteoblasts, osteocytes and osteoclasts, that CB2-deficient mice develop an age-related osteoporosis-like phenotype with high bone turnover, and that a CB2 agonist attenuated ovariectomy-induced bone loss — establishing CB2 as a regulator of bone mass and a candidate osteoporosis target. Hepatic and gastrointestinal CB2 expression is also documented, with roles reported in liver fibrogenesis and in intestinal inflammation and motility. The honest summary is that the immune and bone stories are well developed, and that the liver and gut roles are documented but less completely mapped, with much of the evidence from rodent models rather than human studies.

Contested — caveat. The bone finding is well characterised in mice; the liver and gut roles are supported mainly by rodent models and cell work, and this page does not claim a demonstrated human clinical role for CB2 at either site.

Sources: Ofek O 2006 · Howlett AC 2002 · Munro S 1993