Tween-20 increases the immunoreactivity of apolipoprotein A-I in plasma

Tween-20 (polyoxyethylene 20), a trademark for a sorbitan polyoxyalkalene derivative is used as an emulsifier and detergent. In present studies, we report that Tween-20 is able to reduce the nonspecific binding of radiolabeled apolipoprotein A-I to test tubes. It also enhances the specific binding of 125I-labeled apolipoprotein A-I to anti-apolipoprotein A-I antibodies. Maximal enhancement was achieved at a Tween-20 concentration greater than 0.08%. The results were confirmed by using two different antisera raised in rabbits and goats. Since the immunoreactivity of apolipoprotein A-I in plasma cannot be fully detected by a conventional radioimmunoassay procedure, we have, therefore, studied the effect of Tween-20 on the immunoreactivity of apolipoprotein A-I in plasma. As determined by inhibition radioimmunoassay, we found that Tween-20 drastically increased the immunoreactivity of apolipoprotein A-I using both rabbit and goat antisera. The maximal reactivity was achieved at a Tween-20 concentration of 0.32%. However, Tween-20 did not enhance the immunoreactivity of delipidated plasma. Thus, the results indicate that the plasma lipids may hamper apolipoprotein A-I immunoreactivity and suggest that the nonionic detergent, Tween-20, somehow interacted with HDL lipids or the apolipoproteins and then facilitated the reaction of antigenic reactive site(s) of apolipoprotein A-I with their antibodies.