Biomedical Engineering Reference
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Figure 13.13
Simplifi ed schematic representation of a cross-section of HIV. The central core contains the
viral RNA, consisting of two identical single-strand subunits (approximately 9.2 kb long). Associated with the
RNA are two (RNA-binding) proteins, P7 and P9, as well as the viral reverse transcriptase complex (not shown
above). Surrounding this is the protein P24, which forms the shell of the nuclear caspid. Covering this, in turn,
is a lipid bilayer derived from the host cell, still carrying some host cell antigens. The viral protein, P18, is
associated with the inner membrane leafl et. Viral gp41 represents a transmembrane protein, and viral gp120,
residing on the outside of the lipid bilayer, is attached to gp41 via disulfi de bonds
cells that could initiate an immediate immunological response upon re-entry of the virus into the
host. Studies involving repeat administration of vaccinia virus have, to some extent, confi rmed
this possibility. However, the degree to which such an effect limits the applicability of this ap-
proach in a clinical setting remains to be elucidated.
13.4.5 Development of an AIDS vaccine
AIDS was initially described in the U.S. in 1981, although sporadic cases probably occurred for
at least two decades prior to this. By 1983, the causative agent, now termed HIV, was identifi ed.
HIV is a member of the lentivirus subfamily of retroviruses. It is a spherical, enveloped particle,
100-150 nm in diameter, and contains RNA as its genetic material (Figure 13.13).
The viral surface protein, gp 120, is capable of binding to a specifi c site on the CD4 molecule,
found on the surface of susceptible cells (Table 13.10). Some CD4 negative cells may (rarely) also
become infected, indicating the existence of an entry mechanism independent of CD4.
Table 13.10
Some cell types whose susceptibility to infection by
HIV is believed to be due to the presence of the CD4 antigen on their
surface
T-helper lymphocy tes
Blood monocytes
Tissue macrophages
Dendritic cells of skin and lymph nodes
Brain microglia
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