Cell culture and virus infections C6/36 (Aedes albopictus) cells (ATCC) were maintained in Minimal Essential Medium (MEM) supplemented with glutamine (2 mM), non-essential amino acids, 25 mM Hepes and 10% heat inactivated fetal calf serum. Dengue virus 2, strain 16681 (obtained from Richard Kinney, CDC. Ft. Collins) stocks were amplified in C6/36 cells in MEM (supplemented as above) and 2% heat inactivated fetal calf serum. UV-inactivated DENV was obtained by exposing the same virus stock (used for infection) to UV-light for 3 hr and then conformation of inactivation by two blind passages of the virus on cells for 60 hr per passage. Lack of infectivity was confirmed by plaque assay and immunofluorescence assay.