How HIV Evades the Immune System: Antigenic Variation & MHC-I Downregulation

1. Antigenic variation: HIV constantly changes the structure of its outer coat protein, called the envelope, which is the target of most antibodies. This allows the virus to evade detection and attack by the immune system.

2. Downregulation of MHC-I molecules: HIV can reduce the expression of MHC-I molecules on the surface of infected cells. MHC-I molecules are necessary for presenting antigens to cytotoxic T cells, which are important for killing virus-infected cells.