Opsonizing Antibodies, Host Factors, and the Limulus Assay for Endotoxin

The role of endotoxin in the pathophysiology of human gram-negative rod bacteremia is controversial. Gelation of lysates prepared from the amebocytes of Limulus polyphemus is a highly sensitive means for quantifying endotoxin-like activity in vitro, but variable results have been reported in several clinical studies. We performed limulus tests on plasmas obtained simultaneously with culture-positive blood from 68 patients with gram-negative bacteremia and related results to heat-stable opsonizing activity against the autologous infection strain. Overall, limulus positivity was 52% in this series. Positive tests were observed with 78% of plasmas with opsonic titers is less than or greater to 1:20 but with only 27% of plasmas whose titers were is greater than or equal to 1:80 (P less than 0.005). There was a strong association of positive tests with leukopenia. thrombocytopenia, and more severe underlying disease. In vitro study showed a 10-fold reduction in the sensitivity of the gelation test by antibodies against the endotoxin used and an additional 10-fold reduction when the test system included phagocytic cells.