What does $HIV$ cause a reduction in?

The $ELISA$ test is used for the diagnosis of

Which enzyme helps in the replication of viral $RNA$ genome into viral $DNA$ within macrophages?

The virus responsible for $AIDS$ is an example of a(an):

What is the correct sequence of events that occur after $HIV$ infection in a human body?
$(I)$ Viral $DNA$ enters the host $DNA$
$(II)$ Entry into $T_H$ lymphocytes and replication
$(III)$ Viral $RNA$ is converted into viral $DNA$ by reverse transcriptase
$(IV)$ $HIV$ enters into macrophages
$(V)$ Destruction of $T_H$ lymphocytes
$(VI)$ New virus particles are produced from the host cell

Which enzyme is responsible for integrating the viral $DNA$ (formed after reverse transcription of viral $RNA$) into the host cell $DNA$?