8 You have used fluorescenceactivated cell sorting to separa

8. You have used fluorescence-activated cell sorting to separate blood T lymphocytes from a healthy person and a patient infected with a virus. To sort the cells, you used antibodies against two cell-surface receptors, CD4 and CD8, each conjugated to a different fluorescent dye. Based on the results below, which cell type do you think is depleted by the viral infection: CD4+ helper T cells (H) or CD8+ cytotoxic T cells (C)? Explain your answer in detail? In these dot plots, each cell is represented by a dot whose coordinates are the intensities of CD4 and CD8 signals. Choose H or C as your answer.

Solution

The viral infected cells in patient result in depletion of CD8+ cytotoxic T cells. This is because the virus might have surface antigens that bind to CD8 surface receptors. The antigen bound CD8+ cytotoxic T cells are processed by MHC class II molecules and are presented to macrophages which eliminate them by phagocytosis or neutralization. Therefore, the CD8 cells have depleted in number.