All antigens:

Options

A. Are microorganisms
B. Are not microorganisms
C. React against transplant
D. Do not react against transplant

Answer

### Step-by-Step Text Solution:

1. **Definition of Antigens**: Antigens are substances that can induce an immune response in the body. They are recognized by the immune system as foreign and can trigger the production of antibodies.

2. **Types of Antigens**: Antigens can be found on the surface of pathogens (such as bacteria and viruses) and can also be present in non-living substances (like pollen, certain proteins, and chemicals). This means not all antigens are associated with living microorganisms.

3. **Immune Response**: When antigens are detected, the immune system responds by producing antibodies that specifically target these antigens to neutralize or eliminate them.

4. **Allergens**: Some antigens can cause allergic reactions, which are hypersensitive immune responses. For example, pollen grains can act as allergens for some individuals, leading to allergic reactions.

5. **Transplantation**: In organ transplantation, it is crucial to match the antigens between the donor organ and the recipient. However, not all antigens react in the context of transplantation. Only specific antigens that are mismatched can lead to rejection of the transplanted organ.

6. **Conclusion**: Therefore, the statement "All antigens react against transplant" is incorrect, as not all antigens will necessarily provoke a reaction in a transplant scenario.