Final answer:
Macrophage antigen presentation is increased during the processing of the antigen by the macrophages stage of immunity.
Step-by-step explanation:
The stage of immunity during which macrophage antigen presentation is increased is the processing of the antigen by the macrophages. After engulfing and digesting a foreign antigen, macrophages display a part of the antigen on their cell surface in conjunction with an MHC class II molecule, known as the antigen-embedded MHC class II complex.
This allows lymphocytes of the adaptive immune response, such as helper T cells, to interact with the antigen-embedded MHC class II molecules on macrophages, leading to T-cell activation and the initiation of an immune response.