The correct answer is B: Surface Receptor Proteins
The details:
Antigens are proteins found on the surface of cells that can trigger an immune response. When antigens are part of the body's own cells, they are not recognized as foreign. But when antigens come from outside invaders like bacteria or viruses, the immune system recognizes them as non-self and mounts an immune response.
These surface antigens are examples of surface receptor proteins, which are proteins embedded in the cell membrane that allow the cell to receive signals from other cells. The immune system recognizes foreign surface antigens via antibody proteins that bind specifically to them.
The other answer choices are incorrect:
A. Neurotransmitters transmit signals between neurons, not between immune cells and antigens.
C. Axons are long nerve fibers that transmit electrical signals away from the cell body of a neuron.
D. Dendrites are branch-like extensions of a neuron that receive signals from other neurons.
So in summary, antigens are surface receptor proteins that the immune system recognizes, making B the correct answer. The antigens themselves are not neurotransmitters, axons or dendrites.
Hope this explanation helps! Let me know if you have any other questions.