 This study investigated the effects of cylindrospermopsin, CYN, on two human cell lines, THP1, monocytes, and jerkyt, lymphocytes. The results showed that CYN caused significant reduction in cell viability, with mean EC50 values of 6.00 muM and 5.20 muM for THP1 and jerkyt cells, respectively. Additionally, CYN induced cell death primarily through apoptosis in both cell lines. Furthermore, CYN down-regulated the differentiation of THP1 cells into macrophages, while it increased the expression of pro-inflammatory cytokines, including IL2, IL8, TNF-alpha, and IFN-gamma. These findings suggest that CYN may have immunosuppressive properties in vitro. This article was authored by Antonio Cosas Rodriguez, Oscar Sebadero Dominguez, Maria Porta, and others.