The Immunomodulatory Activity of Some Maltese Medicinal Plants: Tradition, Science and Future Prospects

Aims: To review previous studies conducted on some Maltese medicinal plants for their
immunomodulatory effects on lymphocytes.
Methodology: Human peripheral lymphocytes were obtained from the whole blood of human healthy
volunteers. Several extracts were obtained from Olea europea L., Ephedra fragilis Desf., Aster
squamatus (Sprengel) Hieron., Glebionis coronaria (L.) Tzvelev, Calendula arvensis L., Carlina
involucrata Poir., Dittrichia viscosa (L.) Greuter, Galactites tomentosa Moench, Inula crithmoides L.,
Leontodon tuberosus L., Reichardia picroides (L.) Roth, Sonchus oleraceus L. and Ecballium
elaterium (L.) A. Rich. These extracts, pure metabolites and phytohaemagglutinin were tested on both
resting and stimulated lymphocytes. The blastogenic transformation was monitored by morphological
observations and biochemical tests using the WST-1 tetrazolium reagent and the LDH cytotoxicity
assay.
Results: This current study collates all previous studies. Most of the extracts tested exhibited
lymphocyte activation, with the blastogenic transformation. Some extracts exhibited comparable
activity to that of PHA. Metabolites showing such effects include oleuropein, ephedrine, cucurbitacin E
and flavonoids. Extensive research on cucurbitacin E reveals that, in lymphocyte-cancer cell cocultures,
this metabolite induces lymphocyte activation, which in turn provokes cytotoxic effect on
cancer cells.
Conclusion: The effects of extracts on the lymphocytes was exhibited by several extracts. In the
case of oleuropein, ephedrine and cucurbitacin E, the relationship between structure and function can
be deduced. However, the extracts from the Asteraceae family contained flavonoids, but no further
chemical characterization was carried out. This review recommends further chemical characterization
of the extracts and in depth analysis of the mechanisms for lymphocyte activation by plant
metabolites. On the other hand, this study shows the potential use of these extracts to boost the
immune system, alongside chemotherapeutic agents.