Antibodies are secreted by

The correct option is plasma cells.

Step-by-step Explanation:

1. Understanding Antibodies: Antibodies, also known as immunoglobulins (Ig), are specialized protective proteins produced by the immune system to identify and neutralize foreign substances, such as bacteria and viruses.
2. Role of B Lymphocytes (B cells): When a foreign antigen enters the body, specific white blood cells called B lymphocytes recognize it. Upon activation by the antigen, these B cells undergo rapid division and differentiate into specialized effector cells.
3. Formation of Plasma Cells: The fully differentiated form of B lymphocytes is the plasma cell. Plasma cells function as antibody factories; they possess an abundant rough endoplasmic reticulum, allowing them to synthesize and secrete large volumes of soluble antibodies into the blood and lymph.
4. Analysis of other options:
- Adipose cells: Also known as fat cells, their primary function is to store energy in the form of lipids and provide insulation, not to produce antibodies.
- Reticular cells: These cells synthesize reticular fibers and provide structural support (a cellular framework) for lymphoid organs, but they do not secrete antibodies.
- Mast cells: These cells play a key role in inflammatory and allergic responses by releasing chemical mediators like histamine and heparin when triggered, but they do not produce antibodies.