Studies of T, B, and "null" blood lymphocytes in normal persons of different age groups.

The numbers of T, B, and "null" blood lymphocytes were determined in 216 normal healthy persons, whose ages ranged from 20 to 94 years. No change was found in the numbers of T or B lymphocytes with increasing age of the subjects, whereas both the total lymphocytes and the number of "null" lymphocytes decreased just significantly with age (p less than 0.05). The response of blood lymphocytes to phytohaemagglutinin in vitro was measured in 25 subjects aged 20-30 years and compared with the response in 23 subjects aged over 60 years. There was no significant difference in the response of the two groups.