الفهرس 
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Abstract
Immunity is the body ability to identify and resist harmful pathogen. The immune system has a multilayered construction, with several stages of defenses. The skin is the first barrier of immunity. Then, physiological barriers take place. If a pathogen escaped these barriers, it deals with innate immunity as well as adaptive immunity. Both systems consist of number of molecules and cells that interact in a complex way to detect and eliminate any threat. In recent years, there is an upsurge in the clinical use of natural products or their derivatives due to being free from serious toxic effects and better efficacy. Additionally, steady increase in the resistant microorganism strains to antibiotics and serious averse manifestations brought about by the synthetic drugs has incited researchers to search for natural immunomodulators to fight different infections (Shukla et al., 2014). Natural drugs are reckoned to enhance the resistance of the human body towards various infections and numerous plants have been reported to have immunomodulatory activities (Čolić et al., 2002). Many natural anti-infective medications are believed to exert their effects not just by affecting the pathogen directly, alternately, at least a part of their impaction is underhanded, by stimulating innate and adaptive defensive mechanisms of the body (Shukla et al., 2014). Mechanisms of action of an immunomodulator goes mainly through stimulation of phagocytosis, activation of macrophages, stimulation of lymphoid cells, enhancement of nonspecific cellular immune function, increasing natural killer cell numbers and nonspecific mediators of immune system, increasing the production of antigen-specific antibodies, counter the effect on leukopenia induced by chemotherapy, and increasing total counts of circulating white blood cells and induction of variety of cytokine levels. Several in vivo and in vitro models are available for screening of an immunomodulatory activity of an agent. Although the golden way to discover and evaluate a drug is in vivo “whole animal” model but it has high cost and low efficacy, so the in vitro models may produce alternative way to screen and assay wide range of compounds without taking the risk of animal study. Lymphocyte transformation assay (LTA) measures the extent of clonal proliferation of lymphocytes that cultured in short-term tissue culture under specific conditions when in vitro stimulated by a molecule, antigen or mitogen. This can assess the ability of some compounds to induce non-specific immunity which correlates with immunomodulation. In this study, fifty plant alcoholic extracts were screened for their potential immunomodulatory activity using in vitro human lymphocyte transformation assay. Among the screened extracts, Aralia victoria, Boswellia carteri, Cyperus rotundus, Ginkgo biloba, Glycyrrhiza glabra, Olea europaea and Rosmarinus officinalis were capable to induce 96.7%, 32.2%, 11.1%, 5.6%, 25.6%, 13.3% and 2.2% of lymphocyte transformation respectively in ranking with standard mitogen, Concanavalin-A which induced 20.5% of transformation. Subsequently, each extract was further subjected to bio-guided fractionation using Petroleum-ether, Dichloromethane, Ethyl acetate, Methanol and Distilled water. The bio-guided fractionation revealed that the Dichloromethane fraction of Glycyrrhiza glabra and the Petroleum-ether fraction of Boswellia carteri containing mainly triterpenes, showed activity of 86.0% and 28.0% respectively. This finding promoted us to pursue a comprehensive study on the possible contribution of the commonly known triterpenes of Glycyrrhiza glabra “Glycyrrhizin glycoside” as well as its semisynthetic derivatives as potential immunomodulators using human lymphocyte transformation assay. Following glycoside isolation, semisynthetic reactions yielded fourteen derivatives, of which, five derivatives are recorded as new derivatives (J9-J12 & J14). In addition to nine known derivatives (J1-J8 & J13) screened for the first time for their immunomodulatory action using LTA. Among the fifteen screened compounds, J2 & J9 produced the highest activity (77% & 94.6% respectively), this may be explained by presence of H-bond donor groups (free 3-OH in J2 & N-H in J9). It is worth noted that (Shahlaei et al., 2013) reported the importance of OH group of pentacyclic triterpenes at C3 for the activity. However, the presence of phenyl substitution on N-H may explain the superior activity of J9 over J2.
Compounds J3, J7, J10 & J12 produced about 50.0% transformation and compounds J4, J5, J6, J8 & J11 showed less than 50.0% transformation, while compounds J1, J13 & J14 produced the lowest activity (less than 20.0%).
Other mechanistic biological assays as ABTS●+ antioxidant assay and cytotoxicity assay were pursued in an attempt to disambiguate other mechanisms of action. The compounds showed non-significant antioxidant power that excluded this pathway, low cytotoxic activity which may indicate their immune-selectivity. It could be concluded that the semisynthesized derivatives as well as some natural products can produce immunomodulation “either stimulation or suppression” which may provide support to achieve the healthy state in normal or diseased patients. Further investigation on other experimental models of immunomodulation and clinical studies are recommended before clinical application.