Analysis of treatment in childhood leukaemia. III. Independence of lymphopenia induced by irradiation and by chemotherapy.

Lymphopenia induced by treatment for acute lymphoblastic leukaemia is analysed and discussed in relation to the type and incidence of infection occurring in those patients during complete remission. Blood lymphocytes can be placed into three largely independent groups: (1) those lymphocytes susceptible to long-term depletion following irradiation; (2) those lost from the blood during and for a short period after maintenance chemotherapy with methotrexate and 6-mercaptopurine; and (3) the remainder which are not depleted by irradiation or maintenance chemotherapy. The number of cells in each compartment varies from child to child and probably with age but on average is about 1.2 x 10(9)/1. for group 1, 0.7 x 10(9)/1. for group 2 and 0.4 x 10(9)/1. for group 3. Conventional lymphocyte typing crosses these barriers in that: Group 1 consists mainly of E-rosetting cells and cells which show a mitotic response to phytohaemagglutinin; Group 2 also contains E-rosetting cells but contains a major proportion of blood lymphocytes with surface immunoglobulin and essentially all antibody dependent cytotoxic lymphocyte (K-cell) activity; Group 3 comprises E-rosetting cells and a few immunoglobulin-staining cells.