Effect of Total-Body X-Irradiation on the Susceptibility of Mice to Escherichia coli Endotoxin

Infection may be an important contributing factor to mortality occurring during certain phases of the syndrome which follows total-body X-irradiation. After such irradiation, a number of animal species have shown an increased susceptibility to infection after challenge with a variety of pathogenic and relatively nonpathogenic bacteria, viruses, fungi, rickettsiae, and protozoa (1). Susceptibility of an irradiated animal to certain bacterial toxins is also increased (1, 2). Spontaneous overwhelming fatal bacteremia, usually caused by Gram-negative bacteria indigenous to the lower alimentary tract, is common in mice during the second week after X-irradiation (3). Endotoxin (somatic antigen, pyrogen, or lipopolysaccharide), which can be liberated by breaking down Gram-negative bacteria, is toxic and may be the important factor in death resulting from bacteremia caused by Gram-negative bacteria (4). The present studies were undertaken to ascertain whether an increase in susceptibility to endotoxin occurred after sublethal X-irradiation and whether changes in susceptibility to endotoxin were correlated with the appearance and disappearance of the leukopenia. If an early increase in susceptibility to endotoxin occurs, the prompt control of Gram-negative infections in individuals with traumatic wounds and concomitant X-irradiation assumes increased importance.