It is entirely possible that an individual not infected with HIV has antibodies which may give a positive result in the HIV ELISA. This is called a false positive. One reason for this is that people (especially women who have had multiple pregnancies) may possess antibodies directed against human leukocyte antigens (HLA) which are present on the host cells used to propagate HIV. As HIV buds from the surface of the host cell, it incorporates some of the host cell HLA into its envelope. False negatives can occur during the window between infection and an antibody response to the virus (seroconversion).