Final answer:
Plasma cells, a type of lymphocyte, secrete antibodies as part of the immune response.
Step-by-step explanation:
Plasma cells are a type of lymphocyte that secrete antibodies. These cells differentiate from B cells in response to antigen binding, and they contain a large amount of cytoplasm packed with protein-synthesizing machinery known as rough endoplasmic reticulum. Once activated, plasma cells secrete soluble antibodies, which play a crucial role in the immune response.