Role of CB2 in the Immune System Explained
Discover the critical role of CB2 receptors in the immune system, their interaction with cannabis compounds, and how they contribute to overall health.
Cannabinoid receptors are membrane proteins that bind THC, CBD, and the body's own endocannabinoids. The confirmed list holds two entries: CB1 and CB2. Researchers also track a wider group of cannabinoid-related targets, including GPR55, GPR18, GPR119, PPARalpha, PPARgamma, TRPV1, and 5-HT1A. Only CB1 and CB2 carry official cannabinoid receptor status under international nomenclature.
The Two Canonical Receptors
CB1 (gene CNR1)
CB1 sits on presynaptic terminals and couples to Gi/o proteins, which lowers cAMP and dampens neurotransmitter release. Density is highest in the cortex, hippocampus, basal ganglia, and cerebellum, with lower expression in liver, fat tissue, gut, and peripheral nerves. THC binds CB1 as a partial agonist. CBD shows weak affinity at this site and acts as a negative allosteric modulator at lower concentrations.
CB2 (gene CNR2)
CB2 was cloned in 1993 and shows about 44 percent sequence identity with CB1. It dominates on immune cells: microglia, macrophages, B cells, spleen, and tonsils. THC binds CB2 with roughly similar affinity to CB1, while many synthetic cannabinoids favor one receptor over the other. Small CB2 populations appear in brainstem and some neurons.
The Wider List of Cannabinoid-Related Receptors
- GPR55: an orphan GPCR sometimes called CB3. It responds to lysophosphatidylinositol and to THC and CBD at higher concentrations.
- GPR18: proposed target for N-arachidonoylglycine (NAGly) and a candidate for THC and CBD activity.
- GPR119: binds oleoylethanolamide and other lipid messengers, with links to insulin release and appetite.
- PPARalpha and PPARgamma: nuclear receptors that change gene transcription when activated by CBD, THC, and endocannabinoids.
- TRPV1: the capsaicin ion channel, opened by anandamide and by CBD.
- 5-HT1A: a serotonin receptor that CBD activates directly.
- Glycine and GABA-A receptors: ion channels modulated by endocannabinoids and CBD, without direct cannabinoid binding sites.
How Researchers Confirm a New Cannabinoid Receptor
- Identify an orphan receptor that responds to a cannabinoid ligand in a screening assay.
- Test binding with a radiolabeled agonist such as CP-55,940 across a range of concentrations.
- Measure downstream signaling, such as GTPgammaS binding or cAMP inhibition, to confirm G protein coupling.
- Block the response with a selective antagonist or a receptor knockout to rule out off-target effects.
- Compare potency values against CB1 and CB2 and submit the data to the IUPHAR nomenclature committee.
What the List Means for Product Labels
Marketing copy that claims a product "targets all cannabinoid receptors" oversells the science. THC and CBD reach CB1 and CB2, and they touch several of the related targets above, but affinity varies by compound, dose, and tissue. GPR55, GPR18, and GPR119 remain unconfirmed as true cannabinoid receptors. When you read a strain description or a lab report, treat CB1 and CB2 as the established sites and everything else as an active research area.