To investigate the association between extracts of ginkgo and the immune system by determining changes in natural killer (NK) cell activity and surface markers in human NK cells and by analyzing for surface markers.

Natural killer cell activity was determined in peripheral blood samples of three subjects who received ginkgo daily (250 ml/day; (ginkgo concentration 40 mg/ml) for 14 days by the non-radioisotopic Europium (non-RI Eu) release assay. Peripheral blood samples were taken three times during the study period: before ginkgo sample ingestion, on day 7 after ginkgo ingestion, and on day 14 after ginkgo ingestion). The peripheral blood samples were also analyzed for surface markers (CD56, CD3, CD19, CD20, CD4, CD8) using a fluorescence-activated cell sorter (FACScalibur).

The non-RI Eu release assay revealed that the ingestion of ginkgo extracts elevated NK cell activity in the subjects, with the highest activity recorded following treatment with an extract at a concentration of 400–800 μg/ml. The analysis for surface markers using the FACScalibur showed that the expression of CD56 ( NK cell surface marker) was elevated and the expression of CD19 had dropped in our subjects by day 14 of ginkgo ingestion. There was no significant difference in surface markers after 7 days of ginkgo ingestion.

Ginkgo extracts were found to affect immunological activities and surface markers (CD56) in human NK cells. Our results also reveal an optimal range of ginkgo concentration—from 400 to 800 μg/ml—within which its immunopotentiating activity is highest. It took at least 2 weeks to affect surface markers in human NK cells after ginkgo ingestion, and surface markers were not affected after 7 days of ginkgo ingestion.