The key cell types involved in the acquired immunity include all EXCEPT:
The main physiological role of red blood cells (RBCs), or erythrocytes is to transport gases (O2, CO2) from the lung to the tissues and to maintain systemic acid/base equilibria. 
In addition, RBCs are well equipped with antioxidant systems, which essentially contribute to their function and integrity.
They are not involved in acquired immunity.
B lymphocytes
Erythrocytes
T lymphocytes
Antigen presenting cells (APC)