Here's a breakdown:

* B cells are a type of white blood cell that are responsible for humoral immunity. They produce antibodies that specifically target and neutralize pathogens.

* Plasma cells are the fully differentiated form of B cells. They are antibody factories, churning out vast quantities of a single type of antibody.

* T cells are another type of white blood cell, responsible for cell-mediated immunity. They directly attack infected cells or cancer cells.

Key point: While B cells and T cells are both crucial for immune responses, plasma cells are only derived from B cells, not T cells.