What aspect of cells does the forward scatter (FSC) indicate in flow cytometry?

Forward scatter (FSC) in flow cytometry primarily measures cell size. When cells pass through a laser in the cytometer, the light that is scattered in the forward direction is directly related to the dimensions of the cell. Larger cells tend to scatter more light than smaller cells, allowing the instrument to generate a profile based on size.

This measurement provides critical information for differentiating between different cell populations based on their size, which can be essential in various applications, such as identifying and characterizing different immune cell types or analyzing tumor cells. The FSC value helps to create a preliminary gating strategy, guiding further analysis based on additional parameters that might include cell granularity or specific surface markers.

In contrast, other aspects such as cell density, surface markers, and viability are assessed through different parameters or techniques. Cell density pertains to the concentration of cells in a sample but isn't determined directly through FSC. Cell surface markers are analyzed using fluorescence emitted by specific antibodies bound to cell surface antigens, and cell viability typically involves other techniques such as using viability dyes that can indicate the functional state of the cell.