Deficiency of serum bactericidal activity against Salmonella typhimurium in sickle cell anaemia

Systemic salmonellosis is a recognized complication of sickle cell anemia (SCA). In our initial study of SCA host defences against salmonella, we evaluated the bactericidal activity of serum against Salmonella typhimurium. When compared to controls, sera from eight out of nineteen SCA patients were deficient in bactericidal function. Levels of factor B, haemolytic complement and agglutinating antibody were similar in SCA and control sera. However, abnormalities that might theoretically account for the decreased antibacterial activity were observed in many SCA sera. These abnormal findings included: (a) defective function of the alternative complement pathway (decreased bacterial killing in the presence of Mg EGTA); (b) low serum C3 concentration; and (c) decreased total iron-binding capacity (TIBC), with a resultant increase in per cent saturation of iron-binding capacity. Of these deficiencies only the abnormal alternative pathway function was significantly associated with decreased serum bactericidal activity. A suggested function of serum bactericidal activity is prevention of bacteraemia by susceptible organisms. Thus diminished serum bactericidal capacity may increase the risk of Salmonella bacteraemia in some individuals with sickle cell disease.