What are antibodies primarily responsible for in the immune system?

Antibodies play a crucial role in the immune system primarily by neutralizing foreign objects such as bacteria and viruses. These proteins are produced by B cells in response to specific antigens, which are substances recognized as foreign by the immune system. Once antibodies bind to these antigens, they can mark the invaders for destruction by other immune cells, prevent pathogens from entering or damaging cells, and neutralize toxins produced by bacteria. This specific action is essential for the body's defense mechanisms, allowing it to effectively combat infections and protect overall health.

The other options relate to different functions within the body. Transporting oxygen in the blood is primarily the role of hemoglobin in red blood cells, while regulating blood sugar levels is managed by hormones such as insulin and glucagon. Producing hormones for metabolic processes involves various organs, including the pancreas and thyroid, rather than antibodies. Therefore, understanding the specific role of antibodies emphasizes their importance in immune defense, distinguishing them from functions related to other biological processes.