Step 1: Antibody Function. Antibodies (immunoglobulins) are immune system proteins that identify and neutralize foreign invaders like bacteria and viruses.
Step 2: Antibody-Producing Cells. Antibodies are produced by a type of white blood cell.
(1) B-lymphocytes: Activated B-lymphocytes differentiate into plasma cells, which are antibody producers. Therefore, B-lymphocytes directly produce antibodies.
(2) & (4) Helper T cells & T-lymphocytes: T-cells are essential for immune response, but do not produce antibodies. Helper T-cells activate B-cells and other immune cells.
(3) Nerve cells: Nerve cells are part of the nervous system and do not produce antibodies.
Conclusion: B-lymphocytes (specifically, plasma cells) directly produce antibodies.