<P> The integrated viral DNA may then lie dormant, in the latent stage of HIV infection . To actively produce the virus, certain cellular transcription factors need to be present, the most important of which is NF - κB (nuclear factor kappa B), which is upregulated when T cells become activated . This means that those cells most likely to be targeted, entered and subsequently killed by HIV are those currently fighting infection . </P> <P> During viral replication, the integrated DNA provirus is transcribed into RNA, some of which then undergo RNA splicing to produce mature mRNAs . These mRNAs are exported from the nucleus into the cytoplasm, where they are translated into the regulatory proteins Tat (which encourages new virus production) and Rev. As the newly produced Rev protein is produced it moves to the nucleus, where it binds to full - length, unspliced copies of virus RNAs and allows them to leave the nucleus . Some of these full - length RNAs function as new copies of the virus genome, while others function as mRNAs that are translated to produce the structural proteins Gag and Env . Gag proteins bind to copies of the virus RNA genome to package them into new virus particles . </P> <P> HIV - 1 and HIV - 2 appear to package their RNA differently . HIV - 1 will bind to any appropriate RNA . HIV - 2 will preferentially bind to the mRNA that was used to create the Gag protein itself . </P> <P> Two RNA genomes are encapsidated in each HIV - 1 particle (see Structure and genome of HIV). Upon infection and replication catalyzed by reverse transcriptase, recombination between the two genomes can occur . Recombination occurs as the single - strand (+) RNA genomes are reverse transcribed to form DNA . During reverse transcription, the nascent DNA can switch multiple times between the two copies of the viral RNA . This form of recombination is known as copy - choice . Recombination events may occur throughout the genome . Anywhere from two to 20 recombination events per genome may occur at each replication cycle, and these events can rapidly shuffle the genetic information that is transmitted from parental to progeny genomes . </P>

Macrophage is likely to be a target of hiv because