In this report, we validate that data from immunological investigations of seven Echinacea species may be analyzed phenetically to compare similarities and differences among species. Our demonstration included the acquisition of original data. We consider each of these aspects separately below, as well as possible applications. While we used Echinacea in this report, the system outlined here might be applicable to other medicinal plant taxa.
Consideration of Original Data
extracts used in this study either had no effect on or stimulated production of the cytokines surveyed (). Five species (E. angustifolia
, E. paradoxa
, E. purpurea
, E. simulata
, and E. tennesseensis
) stimulated production of IL–1β and TNF–α, but did not augment IL–2 production. Two other species, E. pallida
and E. sanguinea
, did not influence levels of any of these three cytokines. Though the extracts tested here are the same as those reported elsewhere (Senchina et al. 2005
), a direct comparison between the two studies is difficult due to numerous differences in experimental design (mode of stimulation, extract time of storage).
In contrast, IL–2 is a marker of T–cell activation associated with adaptive immunity (Smith 1984
). Our results are consistent with those from previous reports (Luettig et al. 1989
) but in contrast with other reports showing application of Echinacea
extracts to cell cultures induces production of IL–2 (Bodinet et al. 2002
; Cundell et al. 2003
). Again, these differences are likely due to differences in experimental design, such as choices of model organism, extract type, and species selected.
These results also suggest that Echinacea
may influence innate immunity to a greater extent than adaptive immunity based on the limited number of parameters that were evaluated. This observation is consistent with previous findings from our lab, as well as findings from other investigators (Goel et al. 2005
; Randolph et al. 2003
The result of the phenetic analysis is shown in . Echinacea pallida and E. sanguinea clustered tightly together and separate from all other taxa. Among the remaining five species, E. angustifolia and E. simulata were more similar to one another than to the remaining three species E. paradoxa, E. purpurea, and E. tennesseensis. Finally, the immune response profiles of E. paradoxa, E. purpurea, and E. tennesseensis were approximately equidistant from each other and from the E. angustifolia + E. simulata species-pair. One key observation is that the three species employed commercially (E. angustifolia, E. pallida, and E. purpurea) were widely separated from one another on the dendrogram.
Possible Applications for Phytomedicine
Multivariate relationships among species-specific immune responses may help inform phytomedicinal investigations. For example, it can be seen from that Echinacea pallida tends to exhibit no or suppressive immune modulation, whereas E. angustifolia tends to exhibit mostly enhancing effects on immune function. Our dendrogram suggests that E. angustifolia and E. pallida have very different immunomodulatory capabilities from one another. It also suggests that if an immunosuppressive effect is desirable, species such as E. pallida and E. sanguinea should be favored; likewise, if enhanced immune responses are desired, species such as E. angustifolia and E. simulata should be selected. It is important to stress that these data are based on the testing of only ethanol decoctions and water infusions from a representative sampling of species and accessions; the interpretation is thus limited to these extract types. Different immunomodulatory properties may be obtained by different extraction methods from different accessions.
Our results suggest that different Echinacea spp. act heterogeneously on immune function. Scientists studying Echinacea frequently report findings from only one species. The data presented here indicate that there is not one “representative” species of Echinacea, and that immune effects are highly contingent on species selection, extraction technique, and extract storage conditions. This has important ramifications for further investigations of the immunomodulatory activity. As reviewed above, studies disagree as to Echinacea’s effectiveness in the treatment of respiratory infections. Perhaps, as our results suggest, these discrepancies may arise in part due to investigators employing different species.
Possible Applications for Botanical Supplement Industries
Our findings of heterogeneous immune activity among species of Echinacea may be important to the botanical supplements industry. Currently, E. angustifolia, E. pallida, and E. purpurea are used in most Echinacea preparations, either alone or in combination. Species selection may be a potentially critical factor in the manufacture of Echinacea supplements and should be determined based on desired immune outcome. Further, this analysis suggests that many species of the genus (in particular, E. sanguinea and E. simulata) might by worthy of cultivation for phytomedicinal preparations, again based on desired immune outcome.
Immune responses and Evolutionary History of the Genus
While our phenetic analysis do not make any statements regarding evolutionary relationships between the seven taxa studied here, it is instructive to compare our results against two currently competing taxonomic interpretations of the genus. The traditional treatment constructed by McGregor (1968)
, and the treatment employed in this study, identifies nine species in the genus. However, one investigator (Binns et al. 2002a
) more recently has proposed the genus be considered as only four species. Both treatments are based on morphological characters.
Binns’ treatment groups E. angustifolia, E. pallida, E. sanguinea, E. simulata, and E. tennesseensis sensu McGregor as five varieties within the species E. pallida. However, if these five taxa are compared on our dendrogram, we see that they do not cluster as a monophyletic group on the tree; rather, they are interspersed throughout the dendrogram. Additionally, in our phenetic analysis, E. purpurea, which Binns separated distinct from all other taxa, E. purpurea is distant from all other taxa with respect to overall levels of dissimilarity on the dendrogram. Taken together, this phenetic analysis appears more congruent with the taxonomic treatment proposed by McGregor.