At any one time we have around 1,000,000,000,000 lymphocytes either circulating or deposited in our lymphoid organs. There is a high turnover rate of production with 1,000,000,000 new lymphocyte cells being produced every day. However, given the vast bulk of mature lymphocytes this should suggest that most lymphocytes are robust and capable of long life. Human lymphocytes have been confirmed to have the ability to live up to 10 years. I'm going to have a big problem explaining all the subdivisions of lymphocytes we know about.
Lymphocytes are a very heterogeneous population of cells in size shape and function.
Many of the groupings described below are loose collectives. One crossover that does not occur, T lymphocytes will not become B cells or vice versa, but within these two groups pretty much anything goes. Typical non-activated T lymphocytes have very large round nuclei in cells with very little cytoplasm and the cytoplasm has no obvious granules. These cells look a bit like granulocytes of the innate immune system but they are very different cells in function. In our understanding of lymphocytes there has been much investigation into the cell surface molecules these cells express.