Effects of hormones on development and function of lymphoid tissues. Synergistic action of thyroxin and somatotropic hormone in pituitary dwarf mice.

Hereditary pituitary recessive dwarf mice of the Snell—Bagg strain were used in the present experiment to study the effects of thyroxin and somatotropic hormone alone or in combination, on morphology and immunological function of lymphoid tissues and bone marrow. These animals are characterized by early involution of the thymus, cellular depletion in the peripheral lymphoid tissues particularly evident in the medullary cords and by marked signs of hypocellularity in the bone marrow. They also show an evident depression of the primary immune response to sheep erythrocytes (SRBC). Treatment with the hormones, mainly in combination, prevents the thymus involution, the cellular depletion in lymph nodes and induces signs of cellular repopulation in the bone marrow. Only the combination of both hormones completely normalizes the humoral response to SRBC. It is suggested that the primary site of action of the tested hormones is in the bone marrow. As a result, both antigen-sensitive and antibody-producing cells may be affected through their cellular precursors in the marrow.