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Absence of Dengue 2 Infection Enhancement in Human Sera Containing Japanese Encephalitis Antibodies

Ravithat Putvatana^*, Sutee Yoksan, Thavaj Chayayodhin, Natth Bhamarapravati AND Scott B. Halstead^*

^* Department of Tropical Medicine and Medical Microbiology, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96816
Department of Pathology, Ramathibodi Hospital, Bangkok, Thailand
Division of Epidemiology, Ministry of Public Health, Bangkok, Thailand

Sera from 52 young adults resident in a rural area in North Thailand were studied for plaque-reducing neutralizing antibodies against dengue (DEN) viruses types 1–4 and Japanese encephalitis (JE), and for DEN-2 infection-enhancing antibodies using a newly described microtest in the human monocyte cell line, U-937. Infection-enhancing antibody titers in U-937 cells using a simplified micromethod were similar to results obtained by published methods using human peripheral blood leukocytes and a macrotest using U-937 cells. In the sample, there were 23 with antibodies to one or more DEN viruses with or without accompanying JE antibodies; 16 sera demonstrated antibodies only to JE and 13 had no detectable antibodies to any flavivirus. All but two DEN antibody-containing sera enhanced DEN-2 infections in U-937 cells, often to titers of 1:10,000 or greater. By contrast, only one of 16 JE-immune sera enhanced DEN-2 infection in monocytes, and that at a dilution of 1:100. None of the flavivirus-negative sera had DEN-2 enhancing activity. The failure of human anti-JE contrasts with the ability of rabbit anti-JE to enhance DEN-2 infections, but correlates with the absence of recorded instances of dengue shock syndrome in human beings sequentially infected with JE and then a DEN virus. This report seemingly reconciles in vitro and in vivo phenomena, and may provide an opportunity to study mechanisms involved.

Accepted for publication August 18, 1983.

^* Address reprint requests to: Department of Tropical Medicine and Medical Microbiology, John A. Burns School of Medicine, University of Hawaii, 3675 Kilauea Avenue, Honolulu, Hawaii 96816.