Early after HIV infection antibody responses are not impaired; indeed, development of antibodies to the virus envelope and core proteins is the principal evidence for HIV infection and persists until death. In adults, massive activation of B lymphocytes is manifested by a rise in serum immunoglobulin concentration, perhaps due to direct activation of B cells by HIV. This polyclonal activation explains why a variety of false positive serological tests are seen in HIV infection. In young children, the reverse pattern may be seen, with extremely low levels of immunoglobulin sometimes requiring intravenous replacement therapy. Within days or weeks after infection there may be a transient fall in CD4 lymphocyte numbers and a more sustained rise in the number of CD8 cytotoxic/suppressor cells. Among the CD8 cells, expanded oligoclonal populations are frequently seen and as in other acute virus infections, some of these represent a specific response to HIV.
Following this acute reaction, healthy seropositive individuals may have normal numbers of lymphocytes, although the numbers of CD8 cells frequently remain high. Even at this stage, however, in vitro testing may show a lowered response to previously encountered (recall) antigens (tetanus toxoid or purified protein derivative, for example). This seems to be due to poor production of the lymphokine interleukin 2. Individuals may remain healthy for long periods, but a hallmark of disease progression, often prior to the development of new clinical symptoms, is a fall in the number of CD4 lymphocytes. In AIDS the number of CD8lymphocytes also falls.
Biopsy of the lymph nodes in patients with persistant generalised lymphadenopathy shows many enlarged follicles, often infiltrated by CD8 lymphocytes, with depletion of CD4 cells. Even in clinically silent HIV infection, lymph nodes are the site of remarkably active HIV replication. Uninfected cells may also die by apoptosis, initiated by unexplained mechanisms. In the later stages lymph nodes return to normal size and
follicles become “burnt out”, with loss of normal architecture and progressive cellular depletion.
Following this acute reaction, healthy seropositive individuals may have normal numbers of lymphocytes, although the numbers of CD8 cells frequently remain high. Even at this stage, however, in vitro testing may show a lowered response to previously encountered (recall) antigens (tetanus toxoid or purified protein derivative, for example). This seems to be due to poor production of the lymphokine interleukin 2. Individuals may remain healthy for long periods, but a hallmark of disease progression, often prior to the development of new clinical symptoms, is a fall in the number of CD4 lymphocytes. In AIDS the number of CD8lymphocytes also falls.
Biopsy of the lymph nodes in patients with persistant generalised lymphadenopathy shows many enlarged follicles, often infiltrated by CD8 lymphocytes, with depletion of CD4 cells. Even in clinically silent HIV infection, lymph nodes are the site of remarkably active HIV replication. Uninfected cells may also die by apoptosis, initiated by unexplained mechanisms. In the later stages lymph nodes return to normal size and
follicles become “burnt out”, with loss of normal architecture and progressive cellular depletion.
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