The answer is not parasites, or pathogens. These are tested for before the donor and recipient are even matched
The antibody screen will test for antigens. So I believe the answer is Antibodies.
Answer:
Reduce, reuse, and recycle. Cut down on what you throw away.
Volunteer. Volunteer for cleanups in your community.
Educate.
Conserve water.
Choose sustainable.
Shop wisely.
Use long-lasting light bulbs.
Plant a tree.
