Normal lymphocytes are grouped into several different types with different functions. The two main groups are T and B cells. Very early lymphocytes have not yet committed themselves to become either T or B cells. One type of committed lymphocyte is called the B cell and is an antibody producing cell. The antibodies which B-cells produce help to fight off infections. The other type of committed lymphocyte is the T cell which kills viruses, other infectious organisms and cells which are "foreign" to the body. 

It is important to know which type of lymphocytes the leukaemia cells resemble because the different types respond differently to treatment. 

The word acute describes the comparatively rapid progress of the disease if it is left untreated. It has no bearing on the seriousness of the condition or the potential ability to cure the disease.