ABSTRACT

The immuno-modulating effects of leaf extracts of Telfairia occidentalis (Hook F) and Tectona grandis (Linn) on both humoral and cell mediated immune responses were evaluated in vivo. The responding cells were defined by flow cytometry and secretion of various cytokines by ELISA. Structural elucidation of the bioactive molecules responsible for the observed effect was equally attempted. Results of the quantitative phytochemical analyses of the extracts revealed abundance of bioactive compounds such as soluble carbohydrates (1.624 ¤ 0.002; 0.910 ¤ 0.003 mg/100g), tannin (6.593 ¤ 0.228; 5.325 ¤ 0.526 mg/1 00g), flavonoids (3.780 ¤ 0.228; 3.285 ¤ 0.526 mg/100g), saponins (3.285 ¤ 0.526; 0.744 ¤ 0. 004 mg/g), reducing sugars (293.364 ¤ 0.002; nil mg/100g), glycosides (8.683 ¤ 0.003; nil mg/g), terpenoids (2.436 ¤ 0.002; 2.546 ¤ 0.003 mg/100g), alkaloids (3.363 ¤ 2.247; nil mg/100g), phenol (8.574 ¤ 0.002; 8.096 ¤ 4.494 mg/100g) and hydrogen cyanide (0.395 ¤ 0.004; 0.344 ¤ 0.004 mg/g) for Telfairia and Tectona respectively. Acute toxicity studies carried out on the extracts showed no mortality or adverse reaction to the test mice up to a dose of 5000 mg/kg body weight which indicates that they are safe for consumption. The first stage of this study investigated the immune-modulating effect of aqueous and ethanol leaf extracts of Telfairia occidentalis and Tectona grandis on immune-compromised and non-immune-compromised rats. The results of packed cell volume (PCV), total white blood cell (tWBC) count, red blood cell (RBC) count, haemoglobin (Hb) concentration and humoral antibody titre showed a dose-dependent significant (p<0.05) increase in the groups given oral administration of aqueous and ethanol extracts compared to the untreated control groups. Result of the delayed type hypersensitivity (DTH) reaction showed a significant (p<0.05) decrease in mean paw oedema of rats in the test groups compared to the untreated immune-compromised group suggesting an anti-inflammatory effect of the extracts. In the second stage which investigated the immune-stimulating effect of different fractions on immune-compromised rats, the results showed a significant (p<0.05) increase in PCV, tWBC and CD4+ counts of different groups given varying doses of different fractions of the extracts compared to the untreated control. The increased production of CD4+ lymphocytes by the extracts confirmed their relevance in this study. The third stage studied the immune-modulating and antioxidant effect of both methanol fraction and hot water extracts of Telfairia and Tectona. Myelo-suppression by pyrogallol resulted in increased lipid peroxidation. Treatment with the extracts resulted in a significant (p<0.05) decrease in the concentration of malondialdehyde (MDA) in the test groups compared to the untreated control. Results of antioxidants assay showed a significant (p<0.05) increase in serum activities of catalase, glutathione peroxidase and to a less extent superoxide dismutase in the test groups compared to the untreated control group. The concentration of reduced glutathione was significantly (p<0.05) increased in the test groups compared to the untreated control. Similarly the serum concentration of iron, calcium, selenium and vitamin E increased significantly (p<0.05) when compared to the untreated control. There was no significant difference observed in the level of zinc compared to the untreated control. Result of the cytokine assay revealed a significantly (p<0.05) increased stimulation in the serum expression of interleukin-10 and tumour necrosis factor-alpha in both normal and immune-compromised rats given methanol fraction and hot water extracts compared to the untreated control. There was significant (P<0.05) reduction in the level of interleukin-2 and interferon-gamma in most test groups compared to the untreated control. GC-MS and NMR studies on the extracts showed (2E)-3-(3-hydroxy-4-methoxyphenyl) prop-2-enoic acid as the major compound in Tectona grandis while 3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-chromen-4-one and linoleic acid were found to be the bio-molecules responsible the observed effects in Telfairia occidentalis. The study has provided compelling evidence for an immune-modulatory effect of the extracts investigated. It also confirmed that this effect is mediated via action on cytokine expression and synergistic anti-oxidant activity and that moderate boiling does not affect this effect adversely. The two plant extracts performed similarly in most of the parameters determined.