A cytokine-inducing hemagglutinin from small taros

A 22.4-kDa dimeric hemagglutinin was isolated from tubers of Colocasia esculenta cv. 'Small Taro' by employing a purification protocol that involved ion exchange chromatography on Q-Sepharose, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono Q, and FPLC-gel filtration on Superdex 75. The hemagglutinin was isolated from the fraction of the taro extract adsorbed on Q-Sepharose and subsequently adsorbed on Mono Q. The major absorbance peak from the Superdex 75 column constituted purified hemagglutinin. Its hemagglutinating activity could not be inhibited by simple sugars, and was stable after exposure for 30 minutes to temperatures up to 40 degrees C and to ambient pH in the range of pH 2 to pH 13. The activity decreased progressively when the ambient temperature was raised from 40 degrees C to 100 degrees C. Negligible activity was detected at 100 degrees C. The activity plummeted, with about 40% and 10% remaining, 4 minutes and 20 minutes after exposure to 100 degrees C, respectively. About half of the activity remained at pH 0 and pH 1 whereas the activity was completely abolished at pH 14. The hemagglutinin exhibited slight anti-tumor activity toward hepatoma HepG2 cells, and weak mitogenic activity toward murine splenocytes. It induced expression of the cytokines interleukin-1 beta, interleukin-2, interferon-gamma and tumor necrosis factor-alpha. However, it was devoid of anti-fungal activity toward a number of fungal species.