Patients with CLL and hypocomplementaemia have an impaired serum bactericidal activity against the Salmonella minnesota Re mutant.

The bactericidal effect of 25 serum samples from 23 patients with chronic lymphocytic leukaemia (CLL) against the Salmonella minnesota S form and Re mutant has been studied. No killing of the S form was observed in any of the sera tested, whereas a normal bactericidal effect was found against the Re mutant (group 1) in 17/25 sera of CLL patients. By contrast, in 8 serum samples from 6 CLL patients no killing or a markedly delayed killing of the Re strain was observed (group 2). Significant differences in the complement levels were found between the sera of group 1 and group 2. In group 1 mostly normal or elevated complement levels were observed, while in group 2 levels of C4 and C2 were found to be strongly decreased. A significant correlation was found between the bactericidal effect on the one hand and the C4 and C2 levels on the other.