Tetrahydrocannabinol may enhance natural killer cell cytotoxicity in rats
It is well known that Δ9 - tetrahydrocannabinol (THC), the main active component of marijuana, exerts mainly suppressive infl uence on the immune system. Here we present data indicating that THC induce immune enhancing effects. In this study we examined the effects of small doses of THC on the natural killer cell cytotoxicity (NKCC) (51Cr – release assay) and also on the number of NK cells (identifi ed as large granular lymphocytes, LGL) (Timonen method) in the peripheral blood in rats. Animals received acute or chronic (10 days) i.p. injections of THC at the doses of 0.2 and 0.5 mg/kg. It was found that acute injection of THC signifi cantly increased NKCC after the dose of 0.2 mg/kg (+ 131 Δ%; P<0.001 vs. control and + 52 Δ%; P<0.05 vs. 0.5 mg/kg dose). After chronic exposure to THC, a signifi cant NKCC increase was observed after the dose of 0.5 mg/kg (+ 209 Δ%; P<0.001 vs. control and + 97 Δ%; P<0.01 vs. 0.2 mg/kg dose). The number of LGL remained unchanged after both acute and chronic treatment with THC. It has been reported repeatedly that the doses of over a dozen milligrams of THC suppress NKCC. These results negate the common opinion about unidirectional suppressive effects of cannabinoids on the immune system. It seems that the pharmacodynamics rule of hormesis may also concern the infl uence of THC on the immune system.