system
Given the following post, respond as if you're commenting on Reddit:
human
How do T-cells know which cells they've already inspected?

From what I understand, T-cells are constantly traveling in the body, inspecting cells by looking for antigens. If they're self antigens, then the T-cell doesn't attack, whereas if they're non-self, they attack. My question is how does a T-cell know when it just inspected a cell? Does the T-cell leave something behind on the cell to mark it as checked or does the cell itself present something on its surface to indicate that it has just been checked? If there is no such system, then what prevents the T-cells from being stuck in a loop, and just inspecting the same cell over and over?
gpt
It doesn't know.  And it doesn't loop because it's not like the T-cell specifically waits until the current cell under investigation has "passed inspection" before moving on.  The T-cell just moves around, continuously coming into contact with other cells in the neighboring environment, and if it happens to brush shoulders with bad antigens then it triggers an attack.  But if no attack is triggered, it'll just keep on happily moving about.  The key is that the time it takes to trigger an attack is much less than the time it takes a T-cell to "move over" any given cell.