Answer: The plasma cells.
Plasma cells are cells responsible for production of circulating immunoglobulins.
Step-by-step explanation:
Plasma cells are white blood cells that are produced from the bone marrow and they secrete and produce antibodies like immunoglobulin.
Immunoglobulins are antibododies produced by plasma cells that act as immune response by recognizing and binding to particular antigens such as bacteria, viruses in order to destroy them.