A potent 7-lymphocyte antigen is

The correct answer is Phytohemagglutinin

Explanation:

• Phytohemagglutinin (PHA) is a plant-derived lectin primarily extracted from beans, especially red kidney beans (Phaseolus vulgaris). It is known to stimulate lymphocytes, particularly T-lymphocytes, in laboratory settings, making it a potent mitogen for studying immune responses.
• PHA binds to carbohydrates on the surface of lymphocytes, triggering cell division (mitosis) and immune activation. This property is used extensively in immunological research and diagnostic applications.

Other Options:

• Complement: Complement refers to a group of proteins in the immune system that enhances (or "complements") the ability of antibodies and phagocytic cells to clear pathogens from the body. While the complement system is crucial for immune defense, it does not act as a potent antigen or mitogen for lymphocytes.
• Interleukin-1: Interleukin-1 (IL-1) is a cytokine produced by activated macrophages and is involved in the regulation of immune and inflammatory responses. Although IL-1 plays an essential role in modulating immune reactions, it does not directly act as a mitogen for lymphocytes.
• Endotoxin: Endotoxins are lipopolysaccharides derived from the outer membrane of Gram-negative bacteria. They trigger an immune response and can lead to inflammation, but they are not specific stimulators of lymphocyte mitosis or activation. Endotoxins act more broadly and are associated with systemic effects like fever and septic shock rather than direct lymphocyte activation.