Background and Methods: Peripheral blood lymphocytes (PBL) were separated from 2 individuals for flow cytometric analysis. One individual has already been diagnosed with AIDS and the other is not HIV infected. During centrifugation to separate the lymphocytes from the red cells the labels came off the tubes. Now you have no idea which sample is which, so you label them patient 1 and patient 2. Although flow cytometry should never be used to determine if someone has AIDS or is HIV infected, you decide to perform flow cytometry to match the samples with the patients because from your Med-micro lectures you have learned all about HIV, flow cytometry and T cells and you don't have access to an HIV ELISA test kit. The cells were stained with an anti-CD4 antibody coupled to fluorescein isothiocyanate (FITC), a green-yellow fluorochrome and an anti-CD8 antibody coupled to phycoerythrin (PE), a red-orange fluorochrome. Non-specific antibodies labeled with the same fluorochromes are used as controls. Each dot you see in the diagrams is representative of one cell and how it stained. The data will follow.

Please answer the following questions to help you determine which blood sample is from the AIDS patient and which one is from the individual who is not HIV infected.

A clue on how to interpret the flow cytometry data in this module: In an HIV+ individual, HIV infects CD4+ T helper cells and lyses them. The net result is that CD4 cells are depleted from peripheral circulation. This means that there will be very few CD4+ cells available for staining by flow cytometry.