Genetics of natural resistance to thermal injury.

The possible influence of genetic factors in conditioning the host's natural resistance to the lethal effects of severe thermal injury has been studied in 908 rats of comparable age and weight, originating from two outbred, eight inbred, and two congenic strains of animals of defined genetic background. Each animal was exposed to a standard, full-thickness, 40% body surface area skin burn by controlled contact with a heated metal plate. The 21-day postburn mortality was 100% in 217 Fisher (F-344) and 97 ACI male and female rats. The mortality was reduced to 49-63% in an intermediate group of 84 Lewis, 98 Wistar, 48 Sprague-Dawley, 96 Wistar-Furth (WF), and 48 Osborne-Mendel (OM) male rats; 48 female OM rats had a mortality of 86% at 21 days after injury. The same injury produced a mortality in 4% in 90 Buffalo (BUF) and 22% in 41 Brown-Norwegian (BN) males, while females of the same strains exhibited a 21-day mortality of 23% and 54%, respectively. Further studies of the effects of similar injury in two congenic strains of rats derived from some of the inbred lines of animals listed above yielded a 21-day mortality of 50% in 18 BN.1B(BUF) and 20% in 15 BN.1U(WF) male rats, and 65% and 36%, respectively, in females of the same lines. These data point to the importance of genetic factors as a key determinant of host resistance or susceptibility to the effects of severe thermal injury. The segregation of responses to thermal injury in inbred rats into susceptible, intermediate, and resistant groups on the basis of strain origin indicates that such natural resistance may be a quantitative trait. One of the genetic components affecting host resistance is sex-linked. The existence of genetically controlled variations in natural resistance to trauma may be an important determinant of survival and may be a source of guidelines for the triage and clinical care of injured patients. It may also be an important selective factor in evolution.