Prospects for HIV vaccines.

This article initially discusses the types of responses elicited by infectious agents, such as viruses and the role of each response in preventing, limiting, and clearing the infection. An important response is the generation of immunological memory, in both the B and T cell compartments. Generally, attenuated viral vaccines have been highly successful at inducing long-lived immunity but our understanding of the reasons for this comes from the study of model systems, such as murine influenza virus infections. Specific antibody may largely prevent infection and specific cytotoxic T cells and antibody-dependent cell cytotoxic reactions are the main mechanisms for clearing viral infections. Recent evidence shows that for some months after infection by HIV, a strong cytotoxic T (Tc) cell response occurs in infected, asymptomatic individuals; these cells are continuously generated by HIV-infected stimulator cells that most likely also serve as target cells in vivo. A low level of specific antibody is also formed and a number of reasons are listed to explain why HIV escapes antibody-mediated neutralization and infects cells expressing CD4 receptors. Cells of the macrophage/monocyte lineage are also infected and these express Fc and complement receptors; there is the strong possibility that infection of these cells occurred following the formation of complexes of infectious HIV with antibody to the surface antigen and attachment of complement components. The continuous presence of activated Tc cells that, in contrast to many other viral diseases, does not clear the infection strongly suggests that foci of infected cells sequestered from or resistant to immune control become established. These secrete virus that infects other (stimulator) cells.(ABSTRACT TRUNCATED AT 250 WORDS)