Effect of red blood cell stroma on the reticuloendothelial system clearance and killing of Streptococcus pneumoniae

Previous studies from this laboratory have shown that thermal injury can cause sufficient intravascular hemolysis to depress reticuloendothelial system (RES) phagocytic function and that the injection of red blood cell (RBC) stroma depresses RES function and increases susceptibility to experimental shock. The present study evaluated the effect of thermal injury and RBC stroma on susceptibility to infection with Streptococcus pneumoniae as well as the effect of RBC stroma on the RES clearance and killing of the bacteria. The mortality rate following pneumococcal infection was increased after thermal injury from 0% to 100% (P less than .01), and with the injection of RBC stroma (0.5 ml/100 g) mortality increased from 20% to 80% (P less than .01). Hepatic uptake of heat-killed S. pneumoniae was depressed from 64% to 44% of the injected dose following the injection of RBC stroma. RBC stroma depressed complement CH50 levels by 31%. The reduction in the number of viable S. pneumoniae present in the liver between 30 min and 4 hr following bacterial challenge was decreased in animals receiving RBC stroma. This was interpreted as an indication of impaired hepatic bactericidal function and was associated with an increase in the number of circulating viable S. pneumoniae. It is concluded that the increased susceptibility to pneumococcal infection induced by RBC stroma was probably due to an impairment in hepatic clearance and killing of the bacteria. The depressed bacterial clearance could have been contributed to by the stroma-induced decrease in complement levels. This study further supports the hypothesis that the intravascular hemolysis caused by thermal injury contributes to the increased susceptibility to infection following this form of injury.