The use of radioactive isotopes in immunological investigations. 12. The binding of a hapten by antibodies in vivo.

It is well known that haptens combine with antibodies in vitro (Marrack & Smith, 1932; Haurowitz & Breinl, 1933), although the forces which bind them together are comparatively weak. The in vivo neutralization of the physiological or pharmacological effects of haptens by antisera to antigens containing the corresponding determinant groups was demonstrated by Clutton, Harington & Yuill (1938) and by Butler, Harington & Yuill (1940). The former workers injected antisera to thyroxylproteins into rats and showed that in these rats thyroxine caused a smaller rise in the basal metabolic rate than in untreated rats. Butler et al. (1940) partially neutralized the antipyretic action of aspirin in rats by the prior injection of antisera to proteins that had been coupled with the azide of aspirin. In the present study the binding of a hapten by antibodies in vivo has been inferred from experiments of a different type, in which the phenomenon has been investigated more directly. A radioactive hapten (3:5-di-iodotyrosine) has been injected into rabbits immunized against highly iodinated proteins [containing the 3:5-di-iodotyrosyl group as the main determinant group (Wormall, 1930)]. This injected hapten has been shown to persist longer in the plasma of these immunized rabbits than in the plasma of normal rabbits. Previous experiments along these lines by Mulligan (1950) were probably unsuccessful because large doses of di-iodotyrosine