Cyclo(Gly-L-Pro), a cyclic dipeptide, demonstrates significant immunomodulatory activity by stimulating beneficial immune responses while simultaneously suppressing the release of the pro-inflammatory cytokine TNF-α, reducing mRNA expression of IL-1β and IL-6, and inhibiting nitric oxide (NO) production. it has also been shown to enhance memory and improve functional recovery in animal models, indicating substantial potential for neuroscience research due to its neuroprotective and immunostimulatory properties.

Methods: CIK cells were stimulated with Cyclo(Gly-L-Pro) (1, 10, 100 μg/ml), and the expression of MyD88, IL-1β, TNF-α, I-IFN, and IL-8 genes at different time points (2, 8, and 24 h) after stimulation was quantified by real-time fluorescence. Lipopolysaccharide (LPS), a known immunostimulant, was used as a positive control. To analyze whether these compounds were toxic to the cells, changes in cell viability were measured using a methyltetrazole assay. Results: Cyclo(Gly-L-Pro) and LPS significantly increased the transcription level of MyD88 as early as 2 h after exposure; Cyclo(Gly-L-Pro) also induced the gene expression of cytokines such as IL-1β, TNF-α, and I-IFN. Under the experimental conditions, Cyclo(Gly-L-Pro) was not toxic to CIK cells. [1]