Complement and dengue haemorrhagic fever/shock syndrome.

The complement system is activated in DHF/DSS. The peak of activation and the presence of C3a and C5a anaphylatoxins coincided with the onset of shock and leakage. The levels of C3a correlated well with disease severity. This indicated an important role of the complement system in the pathogenesis of shock. Circulating immune complexes as assayed by two standard techniques were not detected in the majority of patients, and if detected were found in small amount. The role of circulating immune complexes in the activation of complement in DHF/DSS needs to be reinvestigated, and other possible mechanisms leading to complement activation should be sought.