Cytotoxic factor-autoantibodies: possible role in the pathogenesis of dengue haemorrhagic fever

During dengue virus infection a unique cytokine, cytotoxic factor (hCF), is produced that is pathogenesis-related and plays a key role in the development of dengue haemorrhagic fever (DHF). However, what regulates the adverse effects of hCF is not known. We have previously shown that anti-hCF antibodies raised in mice, neutralise the pathogenic effects of hCF. In this study we have investigated the presence and levels of hCF-autoantibodies in sera of patients with various severity of dengue illness (n = 136) and normal healthy controls (n = 50), The highest levels of hCF-autoantibodies (mean +/- S.D. = 36 +/- 20 U ml(-1)) were seen in patients: with mild illness. the dengue fever (DF), and 48 out of 50 (96%) of the sera were positive. On the other hand the hCF-autoantibody levels declined sharply with the development of DHF and the levels were lowest in patients with DHF grade IV (mean +/- S.D. = 5 +/- 2 U ml(-1); P = < 0.001 as compared to DF). Only one of the 13 DHF grade IV patients had an antibody level above the 'cut-off' value (mean plus 3 S.D. of the control sera). The analysis of data with respect to different days of illness further showed that the highest levels of hCF-autoantibodies were present in DF patients at > 9 days of illness. Moreover, the DF patients at all time points. i.e. 1-4. 5-8 and > 9 days of illness had significantly higher levels of hCF-autoantibodies (P<0.001) than patients with DHF grade I, II, III and IV. In addition DHF grade I and grade II patients had significantly more positive specimens than DHF grade III and grade IV patients at all time points. These results suggest that elevated levels of hCF-autoantibodies protect the patients against the development of severe forms of DHF and, therefore, it may be useful as a prognostic indicator. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.