What is the function of surface marker proteins like the major histocompatibility complex?

 

1 Surface marker proteins are enzymes that break down food molecules that are then absorbed.

2 Surface marker proteins are receptors for hormones that then send messages out of the cell.

3 Surface marker proteins are ion channels that allow ions to enter the cell.

4 Surface marker proteins are identifiers that allow the immune system to recognize “self” cells.

5 Surface marker proteins are anchoring proteins that attach neighboring cells to each other.