Final answer:
Automated blood cell counters typically use flow cytometry, which employs fluorescently labeled antibodies to count and analyze specific cell populations within a blood sample, such as CD4 T cells for HIV infection monitoring.
Step-by-step explanation:
Classic automated blood cell counters primarily utilize flow cytometry to enumerate and analyze various cell types within a blood sample. This sophisticated technology harnesses the power of fluorescently labeled antibodies to detect specific cell populations based on their distinct markers. For example, in the context of HIV infections, flow cytometry enables clinicians to precisely measure the number of CD4 T cells in a patient's bloodstream—a critical indicator of immune system health. During the procedure, cells are labeled with a fluorescent antibody to a membrane protein and passed through a narrow capillary in single file. A laser activates the fluorescent label, and a fluorescence detector captures the emitted light at a specific angle. This process not only counts the cells but also records their relative fluorescence. Flow cytometry can be further expanded into a technique known as a fluorescence-activated cell sorter (FACS), allowing for the physical separation and collection of cell populations based on fluorescence intensity.