Reduced CD4 cell counts in blood do not reflect CD4 cell depletion in tonsillar tissue in asymptomatic HIV-1...

To investigate whether the loss of CD4 cells seen in peripheral circulation of HIV-1-positive individuals reflects a similar depletion of CD4 cells from lymphoid tissue.

CD4 and CD8 cells in tonsillar mononuclear cell suspensions were quantified relative to tonsillar B cells, as these were thought to remain numerically unchanged in the course of HIV infection. Results were related to the CD4 cell counts in blood and to the clinical status of the patients.

Blood samples and tonsillar tissue were obtained from 13 HIV-1-seropositive individuals and six seronegative controls. B cells and T-cell subsets in mononuclear cells were quantified using a three-colour flow cytometry protocol. Histological sections were morphologically classified and B-cell areas were quantified by morphometry.

The B-cell fraction was confirmed to be relatively unchanged in asymptomatic HIV-1-seropositive individuals compared with controls. The tonsillar CD4 : B-cell ratios in asymptomatic individuals was similar to those seen in controls, whereas the CD4 : B-cell ratios in symptomatic HIV-1-infected individuals were greatly reduced. The tonsillar CD4 : CD8 cell ratios in HIV-1-infected individuals were much lower than those seen in controls, in the asymptomatic group due to a considerable expansion of the tonsillar CD8 cell subset, and in the symptomatic group also due to a loss of CD4 cells.

We found no evidence of CD4 cell depletion in tonsillar tissue in asymptomatic HIV-1-infected individuals despite low CD4 cell counts in blood. Loss of CD4 cells from this lymphoid tissue seems to occur as a late-stage phenomenon correlated with the onset of clinical symptoms.