What is the first step in the process of HIV replication within a host cell?

The process of HIV replication begins with attachment to CD4 receptors on the surface of host cells. This is a critical step because it facilitates the virus's entry into the cell. HIV specifically targets CD4+ T cells, which are essential components of the immune system. The interaction between the viral envelope proteins and CD4 receptors initiates a series of events that allow the viral envelope to fuse with the host cell membrane, leading to the entry of viral RNA and other components into the host cell.

Once attachment occurs, the next steps in HIV replication can proceed, including reverse transcription, where the viral RNA is converted into DNA, and subsequent integration into the host's genome. However, without the initial attachment to CD4 receptors, the virus would not be able to enter the host cell, and replication could not take place. This step is thus fundamental to the viral life cycle and critical for the infection process.