CD4 lymphocytes (T helper cells) have been termed “the leader of the immunological orchestra” because of their central role in the immune response, and their destruction accounts at least in part for the immunosuppressive effect of the virus. When these cells are stimulated by contact with an antigen they respond by cell division and the production of lymphokines, such as interferons, interleukins, tumour necrosis factor and the chemoattractant chemokines. Lymphokines act as local hormones controlling the growth, maturation and behaviour of other lymphocytes, particularly the cytotoxic/suppressor (CD8) T-cells and antibody-producing B lymphocytes. Lymphokines also affect the maturation and function of monocytes, tissue macrophages and dendritic cells.
Macrophages and particularly dendritic cells are important antigen-presenting cells for initiating immune responses of lymphocytes. Not only do they act as a reservoir for the virus but their antigen-presenting function is impaired, with secondary effects on lymphocytes. Monocytes are the precursors to some glial cells and abnormal lymphokine production after HIV infection may have harmful effects on neural tissue and
result in HIV encephalopathy.
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