Immunomodulatory effects of Abelmoschus esculentus L. flower polysaccharide on spleen lymphocytes via TLR4-MAPK-NF-κB signaling pathways

Abstract

Abelmoschus esculentus L., (okra) which is originated in Africa and planted extensively cultivated plant in tropical and subtropical regions. Okra fruits are ideal vegetable and functional food. However, its flowers wither automatically before the fruit is harvested and most of them are discarded as waste, which causes serious waste of resources. The current investigation elucidated the immunomodulatory effects of a new polysaccharide from okra flowers (AEFP22) on spleen lymphocytes as well as the underlying molecular mechanisms. CCK-8 and flow cytometry analyses demonstrated that AEFP22 increased the viability of spleen lymphocytes and affected their cell cycle progression, thereby facilitating the mitosis of T and B lymphocytes. AEFP22 treatment also enhanced the relative CD4⁺/CD8⁺ lymphocyte ratio and increased CD19⁺ lymphocyte proportion. Additionally, the production of cytokines, immunoglobulins, and nitric oxide and the inducible nitric oxide synthase mRNA level also increased notably following AEFP22 treatment. Furthermore, the relative expression levels of MyD88, TRAF6, and TLR4 mRNAs and proteins were considerably elevated by AEFP22. AEFP22 also activated the phosphorylation of downstream MAPK molecules and facilitated NF-κB nuclear translocation. Thus, AEFP22 can induce stimulation of spleen lymphocyte proliferation and differentiation and activate immunoreaction through the TLR4-MAPK-NF-κB signaling pathways.