Resistance to the Action of the Endotoxins of Enteric Bacilli in Man.

The somatic or "O" antigens of the gram-negative, enteric bacilli represent the principal toxic and antigenic constituents of these organisms (1, 2). Injected intravenously in man in minute amounts, these antigens produce marked physiological reactions consisting of headache, malaise, chills, fever and granulocytopenia (1). Following repeated injections, the severity of the successive reactions declines until the patient may show no reaction to the injections. In rabbits injection of these toxic somatic antigens produces similar effects. The decreasing severity of the reactions in the rabbits was shown to be independent of circulating antibody for the antigen injected (2). This "resistance" was also active against certain other somatic antigens which are chemically similar but immunologically distinct (3). Because this resistance is independent of the presence of homologous circulating antibody, the term "tolerance" was suggested (1). The results of further observations on the nature of this tolerance in man are presented here.