On the basis of an immunologic assay method developed with the Boivin endotoxin of E. coli O:113, the behavior of this endotoxin and its antigenic component was studied in animals with septic arthritis produced by the parent organism. A single inoculation of this strain of E. coli into the knee of rabbits established a severe septic arthritis that was accompanied by high spiking fever lasting 2 weeks. Somatic antigen was found in the blood of febrile animals in the absence of bacteremia; this observation indicated that endotoxin was released into the knee by living and dead bacteria in quantities exceeding those that appeared to be bound locally by the articular tissues. In addition to fever, circulating somatic antigen was accompanied by the hematologic changes and immunologic response characteristic of animals given purified endotoxin intravenously and intraarticularly.
E. coli was cultured from the knee for 2 weeks. The infectious arthritis was then replaced by a prolonged sterile progressive suppurative arthritis. Because E. coli somatic antigen was demonstrated in the sterile joint fluid and because a similar sterile arthritis with fever was produced by knee injections of endotoxin, it is possible that the endotoxin elaborated by living and dead bacteria was responsible for both the local tissue damage and the systemic effects that occurred during infection.
Specific antibody against circulating endotoxin reached its peak at 7 days, whereupon the fever began to decline and further antibody production was checked. Since antisera were found to neutralize both the pyrogenic and antigenic actions of endotoxin, the specific immune response may be partially responsible for interrupting these processes during the infectious arthritis due to E. coli.