What alkylamides do at the cannabinoid receptor
The lipophilic alkylamides in Echinacea purpurea and E. angustifolia are the fraction most often credited with immune activity. In cell studies they bind the CB2 cannabinoid receptor expressed on monocytes and other immune cells, and this binding is associated with shifts in the cytokine signal those cells release rather than with broad immune stimulation. Alkylamides are also unusually well absorbed for a plant constituent, crossing the gut wall and appearing in plasma within minutes.
The cytokine effect is described in the literature as modulation, meaning the response can be dampened or tuned rather than simply switched on. This is why the older shorthand of echinacea as an immune booster is an oversimplification.
Prevention versus treatment in the trial record
Clinical trials have been mixed and species and preparation differ widely between products, which makes comparison hard. The pattern that recurs is a modest reduction in the chance or duration of a common cold when taken before or at the very onset of symptoms, with weaker support for shortening an infection already underway. Echinacea is not a treatment or cure for any infection.
This is general educational information, not medical advice. Anyone with an autoimmune condition or taking immune-affecting medication should speak with a qualified clinician before using echinacea.