Radiation Effects on Lymphocytes 141 



X-rays, however, had a relatively slow destructive action on the human 

 lymphocytes. The in vitro and the in vivo findings are in accord. 



SUMMARY AND CONCLUSIONS 



Moderate doses of irradiation accelerate the aging of normal lympho- 

 cytes with death by intranuclear vacuolization and pyknosis. Large doses 

 of irradiation result in death by delayed fixation. These two degenerative 

 chano.es occur both in vitro and in vivo in man and in lower animals. 

 Irradiation also causes early inhibition of mitoses. These radiation effects 

 result in the initial acute destructive stage. In the lymphoid tissue this stage 

 is characterized by (1) rapid destruction of lymphocytes, (2) phagocytosis of 

 the necrotic debris, and (3) no perceptible reaction of the reticular cell to the 

 irradiation. In the blood there is a slight or a severe lymphopenia and the 

 temporary appearance of degenerating and dead lymphocytes. 



Another effect of irradiation is a transient increase in abnormal mitoses 

 which results in the stage of abortive recovery. This stage is characterized 

 by a temporary alleviation of the lymphopenia, by a transient increase of 

 normal and abnormal mitoses, and by the appearance of abnormal cells in 

 lymphoid tissue. The stage of chronic lymphocytic depression is the result 

 of a low level of production of lymphocytes but no increased destruction. 

 Finally, the recovery stage is associated with more or less normal lympho- 

 poiesis, although there is probably some persistent abnormal production 

 giving rise to a small number of abnormal lymphocytes. 



I have reported in this chapter that the in vitro and in vivo findings are in 

 accord on the following points: (1) Irradiation causes death of lymphocytes 

 by intranuclear vacuolization after low dosages and by delayed fixation after 

 high dosages. (2) The lymphocytes of man and lower animals have ap- 

 proximately the same radiosensitivity. (3) Human lymphocytes react more 

 slowly to x-rays than do rat lymphocytes. (4) In general, human leukemic 

 and normal lymphocytes have the same degree of radiosensitivity. (5) The 

 irradiated cell undergoes abnormal mitoses with the production of atypical 

 cells. 



An enormous amount of work has been done in the field of the biologic 

 effects of irradiation. The subject is, however, still in an active state of 

 growth, but there are still many obvious gaps in our knowledge. This 

 study has led me to the belief that there is a need for additional quantita- 

 tive data both in vivo and in vitro. When such data are available, they 

 will provide a means for a better understanding of the fundamental reac- 

 tions of the lymphocyte to x-rays and for a better understanding of the 

 lymphocyte itself. 



