Function of gp 120 of HIV envelop-

Ans. is 'c' i.e., Attachment of CD4 receptor o Target cells for HIV infection are CD4 Help T-cells (major target), monocyte-macrophages, dendritic cells, Langerhans cells, few B lymphocytes and glial cells/microglia in CNS.o The receptor for the virus is CD4 antigen, and therefore the virus may infect any cell bearing the CD4 antigen on the surface this is primarily the CD4 + (Helper) T Lymphocyte. Specific binding of virus to CD4 receptor is by the envelopc glycoprotein gp-120. However, for infection to take place, cell fusion is essential, which is brought about by the transmembrane gp41. Entry of virus into the cells also requires coreceptor moleculei) Tcells (Helper Tcells) have coreceptor CXCR4 and are infected by T-tropic isolates or syncitia-inducing (SI) strains of HIV (X4 virus).ii) Macrophages have coreceptor CCR5 and are infected by M-tropic isolates or non-syncitia-inducing (NSI) strains of HIV (R5 virus).o Virus using both coreceptors (CXCR4 and CCR5) are called R5X4 viruses.o Follicular dendritic cells from tonsil can be infected by HIV without the involvement of CD4.o When HIV infects a cell, the viral RNA is transcribed by reverse transcriptase, first into single stranded DNA and then to double stranded DNA (Provirus). Provirus is integrated into host cell chromosome. This provirus initiates viral replication by directing synthesis of viral RNA, in response to viral promoters. Thus, the sequence in replicationis RNA - DNA - RNA & proteins.HIV infection of a cell | Viral RNA inside the cell |Reverse transcriptaseSingle stranded DNA |Reverse transcriptaseDouble stranded DNA (Provirus) | Integrated into host chromosomes |- Viral promotorsSynthesis of viral RNA and other components