Question

when the memory t cell encounters an antigen on an infected macrophage, what happens?

Explanation:

Memory T - cells recognize the antigen - MHC complex on the infected macrophage. This recognition leads to their rapid activation, proliferation, and differentiation into effector T - cells. Effector T - cells then help eliminate the infected cells.

Answer:

The memory T cell is rapidly activated, proliferates, and differentiates into effector T - cells to help eliminate the infected cells.