Immunomodulatory activity of Asparagus racemosus on systemic Th1/Th2 immunity: Implications for immunoadjuvant potential
Introduction
Asparagus racemosus (AR) Willd. (Asparagaceae) is an important medicinal plant indigenous to South Asian countries. Its medicinal properties are reported in traditional systems of medicine such as Ayurveda, Siddha and Unani (Charak Samhita, 1970). Ayurveda, describes AR as rasayana and galactogogue, which is used to treat various diseases such as ulcer, dyspepsia and debility. Chemically, AR roots contain steroidal saponins known as shatavarins I–IV, iso-flavones and alkaloids including asparagamine and racemosol as major compounds (Saxena and Chourasia, 2001). In last decade, a few pharmacological and immunomodulatory activities of AR have been studied. For instance, AR root extract was shown to restore lymphocyte and neutrophils counts in myelosuppressed animals, which was comparable to lithium and glucan (Thatte and Dahanukar, 1988). In addition, AR roots were also reported to modulate macrophage functions resulting in significant reduction in severity of peritoneal adhesions (Rege et al., 1989). Further, AR hydro-alcoholic extract was found to induce lag in tumor development in experimental animals (Seena et al., 1993). The modulatory effect of AR crude and hydro-alcoholic extracts on TNF-alpha secretion, phagocytosis and neuro-endocrinal secretions is also reported (Bhatnagar et al., 2005, Parihar and Hemnani, 2004, Dalvi et al., 1990, Dhuley, 1997). Previously, we reported immunoadjuvant activity of AR aqueous root extract (ARE) in two different experimental models. In the first model, co-administration with lower immunogenic doses of DPT vaccine resulted in higher anti-pertussis antibody titres and immuno-protection against lethal pertussis challenge (Gautam et al., 2004). While in second, it resulted in myeloprotection and recovery of humoral and cellular immunity in tumor bearing myelosuppressed mice (Diwanay et al., 2004). Overall, these studies project immunostimulant activity of AR, however, its immunological basis still remains unclear.
Modulation of Th1/Th2 immunity is emerging as one of biological targets for such immunostimulants (Romagnani, 2000). Helper T cells (Th) may be subdivided into two cell subsets, termed as Th1 and Th2, according to differences in their corresponding cytokines. Th1 cytokines contribute cell-mediated immunity while Th2 cytokines are responsible for humoral immunity (Warren et al., 1986, Abbas et al., 1996). We have studied possible immunoregulatory effects of ARE on murine Th1/Th2 immunity using SRBC as antigenic stimulus. Flow cytometry was used to monitor immune cell populations. Levamisole is one of the clinically established orally active Th1/Th2 immunomodulators, thus was used as positive control in the entire study (Bozic et al., 2003, Szeto et al., 2000, Argani and Akhtari, 2006). Our study suggests that ARE has cytoprotective, immunorestorative activities with mixed Th1/Th2 response and can be used as vaccine or immuno adjuvant.
Section snippets
Preparation of extract (ARE)
Asparagus racemosus roots were obtained from Green Pharmacy, Pune, India and were correctly identified and authenticated as Asparagus racemosus Willd. (Asparagaceae) by National Institute of Science Communication and Information Resources (NISCAIR), New Delhi, India (vide NISCAIR/RHMD/Consult/06/734/51). A voucher sample is retained and deposited at Agharkar Research Institute Herbarium, Pune, Maharashtra, India. Powdered roots were extracted as aqueous decoction as per Ayurvedic Pharmacopoeia
Standardization of ARE
HPTLC analysis was done on basis of identification and quantification of two steroidal saponins, Shatavarin IV and immunoside that are reported to be present in ARE. The result suggests assay percentages of Shatvarin IV and immunoside in ARE at 8.53 ± 0.38 and 0.038 ± 0.003, respectively.
Effect of sensitization protocol on selected immune markers
As a first step to study effect of ARE on Th immunity, effect of sensitization protocol on selected immune markers was established. Animals were injected pyrogen free saline i.p. with and without SRBC on days 0 and
Discussion and conclusions
Modulation of Th1/Th2 immunity is an important parameter to assess therapeutic efficacy of immunomodulators. Based on affinity towards Th1/Th2 subsets, immunomodulators are generally classified as Th1, Th2 or mixed Th1/Th2 agents. A. racemosus root aqueous extract is known to exhibit immunopharmacological activities under different biological stimuli. However, its efficacy towards Th1/Th2 immunity has not been investigated. The present study demonstrates that ARE has mixed Th1 and Th2 adjuvant
Acknowledgements
Authors are thankful to Regional Research Laboratory (IIIM), Jammu, Council of Scientific and Industrial Research, Government of India for extending the necessary facilities and infrastructure. MG, DP, SM, SG, KS, SSJ and BP are also grateful to Department of Science and Technology, Government of India and Serum Institute of India Ltd for project grant on development of botanical immunomodulators as adjuvants under Drugs and Pharmaceutical Research Program. Thanks to Drs Madhuri Thakar, Kalpana
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