In infected person, HIV enters into macrophages where virus is replicated and gets incorporated with host cell's DNA with the help of enzyme RNA transcriptase. Infected host cells produce virus particles so that host's macrophages act as HIV factors. At the same time, HIV enters into helper T-lymphocytes and replicates to form progeny virus. They again attack blood and helper T-lymphocytes . This disease in T-helper leads to deficient immunity in infected persons.