I was wondering if there was a way you could show how cells are able to determine themselves and foreign invaders in an experiment?

Certainly! One way to demonstrate how cells recognize self from foreign invaders is through a simple lab experiment called a mixed lymphocyte reaction (MLR). This experiment reveals how immune cells, specifically lymphocytes, distinguish between cells that belong to the same individual (self) and those that come from a different individual (non-self).

Here's how you can perform the MLR experiment:

1. Obtain samples: Collect lymphocytes from two different individuals, commonly referred to as donor A and donor B. These can be obtained from peripheral blood or lymphoid tissues.

2. Isolate lymphocytes: Separate the lymphocytes from the collected samples using appropriate techniques like density gradient centrifugation. This will yield a population of purified lymphocytes from each donor.

3. Label the cells: Using different fluorescent dyes, label the lymphocytes from donor A with one color (e.g., green) and the lymphocytes from donor B with another color (e.g., red).

4. Mix the cells: Combine equal numbers of the labeled lymphocytes from donor A and donor B in a culture plate or tube. This allows the cells to interact with each other.

5. Incubate: Place the mixed lymphocyte culture in a suitable incubator to provide optimal conditions for cell growth.

6. Analyze after incubation: After a defined period (e.g., 24 hours), remove a small sample from the mixed lymphocyte culture and prepare it for analysis.

7. Observe under a microscope: Use a fluorescence microscope to examine the cells. Look for interactions between the green-labeled cells (donor A) and the red-labeled cells (donor B).

8. Interpret the results: In a healthy immune system, lymphocytes will recognize cells that express different surface markers (antigens) and initiate an immune response. This can include direct cell-to-cell interactions or the release of signaling molecules. If lymphocytes from donor A and donor B interact, it indicates that the cells are recognizing each other as foreign (non-self).

By observing the interaction or lack thereof between lymphocytes from different individuals, the MLR experiment demonstrates how cells can distinguish self from non-self. This ability is crucial for the immune system to mount an appropriate immune response against foreign invaders while avoiding attacking the body's own cells.