The immune system doesn't detect a specific functional class of membrane proteins. Instead, it detects specific structures on these proteins, known as antigens.

Here's a breakdown:

* Membrane proteins: These proteins are embedded in the cell membrane and play various roles like transporting molecules, receiving signals, and acting as receptors.

* Antigens: These are specific molecules (often proteins, but also carbohydrates, lipids, or nucleic acids) on the surface of cells that the immune system recognizes.

* Immune system recognition: Immune cells have receptors that can bind to specific antigens. When an immune cell encounters an antigen it recognizes as foreign, it triggers an immune response.

So, the immune system doesn't care about the functional class of the membrane protein. It's all about the specific antigen structure. This is why the immune system can target a wide range of cells, pathogens, and even our own cells if they display abnormal or foreign antigens.

Examples:

* Viral proteins: Viruses have proteins on their surface that are recognized by the immune system as foreign.

* Bacterial surface molecules: Bacteria have unique cell wall components like peptidoglycans that trigger an immune response.

* Tumor antigens: Cancer cells can express altered proteins that are recognized as foreign by the immune system.

In summary: The immune system detects a vast array of different antigens, regardless of the functional class of the membrane protein they are part of.