ERVW-1 and infection: Due to the nature of the high-dose challenge employed, and the high levels of anti-envelope reactivity found in serum of this animal, one could speculate about a potential low-level infection not detected by regular viral load measurements, which could lead to development of endogenous anti-Env responses, resulting in an overestimation of the concentration of 5L7 antibody in the anti-SIVmac239 gp140 ELISA employed (see Materials and Methods).