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Plants have been extensively studied since ancient times and numerous important chemical constituents with tremendous therapeutic potential are identified. Attacks of microorganisms including viruses and bacteria can be counteracted with an efficient immune system and therefore, stimulation of body’s defense mechanism against infections has been proven to be an effective approach. Polysaccharides, terpenoids, flavonoids, alkaloids, glycosides, and lactones are the important phytochemicals, reported to be primarily responsible for immunomodulation activity of the plants. These phytochemicals may act as lead molecules for the development of safe and effective immunomodulators as potential remedies for the prevention and cure of viral diseases. Natural products are known to primarily modulate the immune system in nonspecific ways. A number of plant-based principles have been identified and isolated with potential immunomodulation activity which justify their use in traditional folklore medicine and can form the basis of further specified research. The aim of the current review is to describe and highlight the immunomodulation potential of certain plants along with their bioactive chemical constituents. Relevant literatures of recent years were searched from commonly employed scientific databases on the basis of their ethnopharmacological use. Most of the plants displaying considerable immunomodulation activity are summarized along with their possible mechanisms. These discussions shall hopefully elicit the attention of researchers and encourage further studies on these plant-based immunomodulation products as potential therapy for the management of infectious diseases, including viral ones such as COVID-19.

The aim of this investigation was to see if the crude extract of Sarcococca saligna (Ss.Cr) contains chemicals with gut function inhibitory activity by using in vitro and in vivo assays. Ss.Cr caused a dose-dependent (0.03 - 3 mg/mL) inhibitory effect on K+-induced contractions in rat stomach fundus, guinea-pig ileum and rabbit jejunum preparations. The calcium channel blocking(CCB) activity was confirmed when Ss.Cr caused a rightward shift in the Ca++ dose-response curves. It also potentiated, at lower do-ses (0.001 - 0.03 mg/mL), the contractile effect of a fixed dose of acetylcholine (ACh), similar to physostigmine, and suppressed the effect of ACh at higher doses (0.3 - 1.0 mg/mL). Both Ss.Cr and physostigmine inhibited acetylcholinesterase (AChE), in the in vitro assay, confirming the AChE inhibitory activity. In the in vivo studies, Ss.Cr exhibited antidiarrheal and antisecretory activities against castor oil-induced diarrhea and intestinal fluid accumulation in mice. Characteristic steroidal compounds of the plant (saracocine, saracodine, saracorine and alkaloid-C), exhibited a similar combination of AChE inhibitory and CCB activities. Thus this study provides a sound mechanistic base for some of the traditional uses of the plant in hyperactive gut states, in addition to providing the first evidence for verapamil to possess additional AChE inhibitory activity. Furthermore, these characteristic compounds with dual activity may be good candidates for further studies on their usefulness in Alzheimer's disease.

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