Staphylococcal pyrogenic
exotoxin (PE) ty pe C enhanced the susceptibility of rabbits to lethal
shock by
endotoxin by as much as 50,000-fold. A graph of log
PE type C dose used for pretreatment versus log 50% lethal dose of
endotoxin gave a straight line with a slope of approximately -1. Rabbits that received
PE type C alone showed
fevers only, but those given both PE ty pe C and
endotoxin showed initial
fever followed by
hypothermia, labored breathing,
diarrhea, evidence of vascular collapse, and finally death. When a
PE type C dose of 3 micrograms/kg was used, pretreatment of the animals with PE for 2 h before giving the
endotoxin was required to obtain maximal susceptibility. However, when 15 micrograms of
PE type C per kg was utilized, the
endotoxin could be given before, concurrently, or after
PE type C. The capacity of
PE type C to prepare rabbits for enhanced susceptibility to
endotoxin was lost after 24 to 48 h. Animals could be protected from enhanced susceptibility to
endotoxin by prior immunization with either
PE type C or
endotoxin. However, 30% of the rabbits which were immunized with
PE type C failed to develop immunity, and after three
injections of
PE type C, these animals developed gram-negative
bacteremia and succumbed. In addition, rabbits with
diarrhea initially, possibly caused by
Pasteurella infection, died less than 24 h after a single injection of
PE type C.