Changes in antigen expression on B lymphocytes during HIV infection

Involvement of the B cell compartment during HIV infection plays an important role in the development of immune deficiency. The aim of this study was the identification of specific antigen expression changes on B lymphocytes in HIV infection as surrogate markers in this cell population of certain functional aspects that could be easily measured. We investigated the level of expression of a series of constitutive surface markers in B lymphocytes (HLA-DR, CD19, CD20, CD21, CD22) from 30 HIV-seropositive adult patients and 20 normal controls. By means of quantitative flow cytometry, we assessed the number of antigen molecules per cell using standard beads to convert fluorescence intensity into antibody-binding capacity (ABC). We correlated these results with disease stage and cellular markers of immune activation. The expression of CD20 was significantly increased when B cells from HIV-infected individuals were compared with those from uninfected subjects. No differences were found in the density expression of HLA-DR on activated CD3+ T cells between HIV+ and HIV- subjects. In contrast, B cells from HIV+ patients showed a significantly lower number of HLA-DR molecules per cell compared to normal controls. A significantly lower number of CD21 molecules per cell was also found on B lymphocytes from HIV+ patients compared to normal controls. No differences in CD19 and CD22 expression levels on B cells between HIV-infected patients and controls were detected. No differences between HIV disease stages were detected for CD19, HLA-DR, CD21 and CD22. In contrast, differences between stages were found for CD20 expression, which showed significant changes in individuals with less than 200 CD4 T cells/microl. The data presented here demonstrate that B lymphocytes of HIV-infected individuals exhibit specific changes in receptor density expression during HIV infection and that these changes are often correlated with progression of disease, as measured by CD4 counts. No correlations were found between the percentages of HLA-DR+ T cells and the ABC values of the B cell markers studied. These antigen expression modulations may contribute to the humoral abnormalities during HIV infection and to the development of severe, recurrent or multiple bacterial infections. Therefore, quantitative flow cytometry may be of value in HIV infection both for clinical and biological studies. The study of antigen density changes on B cells in HIV infection may allow a better understanding of the humoral immune defects observed in these patients and provide insights into the functional defects of B cell compartment in HIV-infected individuals.