Effect of neonatal thymectomy on the immunological responsiveness of the mouse

Abstract

The effect of thymectomy on the lymphocyte population and immune response of C3H, (Ak $\times $ T6) F$_{1}$ and C 57 BL mice has been investigated. Thymectomy performed in the immediate neonatal period was associated with severe depletion in the lymphocyte population and serious impairment of the immune response of the mature animal to Salmonella typhi H antigen and to allogeneic and heterospecific skin grafts. Clinically, the mice appeared healthy until about 2 to 4 months of age when two-thirds of the animals died from a syndrome characterized by progressive wasting and diarrhoea. Thymectomy in infancy was still associated with some impairment of the immune response to skin homografts particularly when donor and hosts were closely related immunogenetically. Thymectomy after 3 weeks of age was not associated with any significant impairment of homograft immunity. Neonatally thymectomized mice subsequently grafted with thymus tissue were capable of rejecting allogeneic skin grafts and showed evidence of immunity to such grafts. The lymphoid tissue of the thymus-grafted mice appeared normal and was shown to contain cells that had been derived from the thymus graft. It is concluded that, during very early life, the thymus produces the progenitors of immunologically competent cells which mature and migrate to other sites. Present evidence does not, however, exclude the production by the young thymus of a humoral factor necessary to the maturation or proliferation of lymphocytes elsewhere in the body.