| Summary: | Abstract Background The leaf concentrate of Carica papaya is a traditionally acclaimed immunomodulatory remedy against numerous diseases; nonetheless comprehensive scientific validation of this claim is limited. The present study thus investigated the immunomodulatory potential of Carica papaya mature leaf concentrate (MLCC) of the Sri Lankan wild type cultivar using nonfunctional and functional immunological assays. Methods Wistar rats (N = 6/ group) were orally gavaged with 3 doses (0.18, 0.36 and 0.72 ml/100g body weight) of the MLCC once daily for 3 consecutive days. Selected nonfunctional (enumeration of immune cells and cytokine levels) and functional (cell proliferation and phagocytic activity) immunological parameters, and acute toxic effects were determined using standard methods. Effect of the MLCC (31.25, 62.5, 125, 250, 500 and 1000 μg/ml) on ex vivo proliferation of bone marrow cells (BMC) and splenocytes (SC), and in vitro phagocytic activity of peritoneal macrophages (PMs), and their corresponding cytokine responses were evaluated. The phytochemical profile of the MLCC was established using liquid chromatography-mass spectrometry (LS-MS) and Gas chromatography-mass spectrometry (GC-MS). Results Counts of rat platelets, total leukocytes, lymphocyte and monocyte sub populations, and BMCs were significantly augmented by oral gavage of the MLCC (p < 0.05). The highest MLCC dose tested herein significantly reduced pro inflammatory cytokines, Interleukin 6 (IL-6) and Tumor Necrosis Factor α (TNF α) levels of rats (p < 0.05). The in vivo phagocytic index of rat PMs significantly increased by oral gavage of all three doses of the MLCC (p < 0.05). In vitro phagocytic activity of rat PMs were enhanced by the MLCC and triggered a Th1 biased cytokine response. The MLCC at low concentrations elicited ex vivo proliferation of BMC (31.25 μg/ml) and SC (31.25 and 62.5 μg/ml) respectively. Conversely, high concentrations (500 and 1000 μg/ml) exhibited cytotoxicity of both BMC and SC with significant modulation of cytokines. Chemical profile of the MLCC revealed the presence of several immunomodulatory compounds. The oral gavage of the MLCC was found to be safe in terms of both hepatic and renal toxicities. Conclusion The present study established that the mature leaf concentrate (MLCC) of Carica papaya Sri Lankan wild type cultivar is orally active, safe and effectively modulates nonfunctional and functional immunological parameters of rats that unequivocally corroborate the traditional medical claims.
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