Lymphocytes are a category of white blood cell, or leukocyte. The main categories of lymphocytes are B cells and T cells. B cells are responsible for manufacturing antibodies, whereas T cells have more complex roles. Depending on the category of the T cell, it may be responsible for destroying invading cells, for secreting cytokines in response to an antigen, or for activating macrophages and NK-cells. These processes shall be discussed at a later date.
Flow cytometry was previously mentioned, and one application of this technique is in counting specific lymphocyte population. The ELISPOT method was mentioned as well; this technique is used for counting the number of B cells that secrete a specific antibody, or the number of T cells that produce a given cytokine or granzyme.