Lymphocyte Transformation in Megaloblastic Anaemia: Morphology and DNA Synthesis

S ummary . Lymphocytes from six patients with untreated pernicious anaemia and from one patient with folate deficient megaloblastic anaemia were cultured with phytohaemagglutinin (PHA). The mean percentage of cells undergoing transformation (78) was similar to normal. The morphology of the PHA‐stimulated transformed ‘megaloblastic’lymphocytes was distinct from that of PHA‐stimulated normal lymphocytes. Transformed ‘megaloblastic’lymphocytes tended to be larger and to show a more finely reticulated open chromatin pattern than normal transformed lymphocytes. The incorporation of [ 3 H]thymidine into DNA of PHA‐stimulated ‘megaloblastic’lymphocytes was significantly greater than normal. The inhibitory action of deoxyuridine (dU) on [ 3 H]thymidine incorporation into the DNA of PHA‐stimulated lymphocytes was significantly less in ‘megaloblastic’lymphocyte cultures than in normal cultures. Both these observations suggest that there is a block in synthesis of thymine‐DNA from dU in PHA‐stimulated ‘megaloblastic’lymphocytes. The metabolic block in vitamin B 12 deficiency could be partly corrected by vitamin B 12 and completely corrected by folic acid or folinic acid suggesting that the defect was due to lack of folate coenzyme. The abnormality of thymine‐DNA synthesis in ‘megaloblastic’lymphocytes shown here was similar to that shown by other workers in megaloblastic bone marrow cells. The present study provides cytological and biochemical evidence that deficiency of vitamin B 12 or folate causes a derangement of DNA synthesis in the lymphocyte.