Total dietary restriction and thymus, spleen, and phenotype and function of splenocytes in growing mice.

To study the immunological effect of total dietary restriction, BALB/c mice were limited to reduced body growth or maintained at practically constant body weight between 21 and 61 days of age by giving them 70% (R70%) or 55% (R55%) of the average daily food intake of the control group fed ad libitum. Thymus and spleen weight were decreased, but thymus size was maintained in proportion to body weight in R70% mice, whereas the ratio of thymus weight to body weight was significantly decreased in R55% mice. In restricted mice, splenocytes showed a lower percentage of B lymphocytes and a higher percentage of T lymphocytes. Results of stimulation showed that proliferation capacity was increased for B lymphocytes and decreased for T lymphocytes in restricted mice. Our data show the importance of studying the thymus over a period, because normal thymus growth was first greatly impaired by dietary restriction, and subsequent thymus involution was delayed, showing that an isolated comparison between the thymus of growing mice is not enough. Our data show the interest of determining the percentage of lymphocyte populations parallel to their response to mitogen stimulation.