Medicinal Rhodiola imbricata induces protective immune responses against susceptible and resistant strains of Leishmania donovani in murine model

Visceral leishmaniasis (VL) is an infectious disease caused by protozoa, Leishmania. During infection, the cell-mediated immunity of host gets impeded, so immunomodulation using natural products can be considered as an effective therapeutic strategy. The present study deals with the investigation of antileishmanial and immunostimulatory potential of hydro-ethanolic root extract of Rhodiola imbricata (HERERI) in inbred BALB/c mice. The secondary metabolites were analyzed quantitatively. To study the effect of HERERI on promastigotes, assays including inhibitory concentration (IC50) by trypan blue staining, cell cycle arrest by FACS were performed. The splenic parasite load was monitored after 14 days of treatment in BALB/c mice (500 and 1000 mg kg−1 b.wt.). The immunological responses after treatment were recorded in terms of DTH (delayed type of hypersensitivity) reactions, different T lymphocyte’s subtypes and amounts of Th1/2 cytokines. Biochemical assays to analyze the function of liver and kidney were also done along with the histological studies. HERERI contains a considerable amount of flavonoids, phenols and terpenoids. The IC50 of 24.84 ± 0.52 and 46.65 ± 1.90 µg mL−1 against sensitive and resistant strain was obtained, respectively. It also arrested the cell cycle of promastigotes at sub G0-G1 phase. HERERI significantly decreased parasite load and up-scaled the DTH responses. It also polarized the Th1 dominating immune status by upregulation of IL-12, IFN-γ, and TNF-α cytokines and CD4+, CD8+ T cells. It caused no toxicity as biochemical tests and the histological sections were normal as compared to infected animals. Overall R. imbricata rescued mice from VL infection through immunostimulation.