Pathogenic bacteria secrete:

Correct answer: (a) Antigens

Explanation

Pathogenic bacteria carry and release antigens: substances, such as their surface proteins and toxins, that the body recognises as foreign. These antigens make the immune system produce antibodies.

• Antibodies are made by the host's B cells (plasma cells), not by bacteria.
• Antibiotics are made by some fungi and bacteria to kill other microbes; disease-causing bacteria do not secrete them against the host.
• Interferons are proteins that the host's cells release against viruses.