Objective: SARS-CoV-2 is an illness that attacks the respiratory tract's alveoli lining cells. One approach to tackling it is to strengthen the immune system of the body, which has an organ specifically dedicated to defending against diseases. Among the key components of the body's immune system that defend against the SARS-CoV-2 virus are Natural Killer (NK) cells. Sungkai (Peronema canescens Jack) is a plant commonly used by communities to boost their immunity. The aim of this study was to examine the activity and characterization results of Sungkai leaves on Natural Killer cells.
 Method: Sungkai powder was extracted using a 70% ethanol solvent and evaporated using a rotary evaporator. It was then fractionated using n-Hexane and evaporated using a rotary evaporator to obtain a thick fraction. The thick fraction was then chromatographed, resulting in two isolated compounds that were tested in vivo for their immunostimulatory activity using mice as test animals with ethical approval (405/UN.16.2/KEP-FK/2021).
 Results: The study consisted of five groups, including a normal group and four other groups of white mice that had been exposed to the SARS-CoV-2 virus antigen Moderna vaccine 0.0013 ml.
 Conclusion: The results showed that stigmasterol was more effective than Bis(2-ethylhexyl) phthalate in increasing Natural Killer cells' immunostimulant activity.
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