Localization and distribution by age and species of an avian thymus-specific antigen

The chicken thymus-specific antigen (T1) was localized within certain cell types of the thymus using an indirect immunofluorescent (FA) test. One of the cell types was similar to small mononuclear cells, whereas the other was much larger and irregular in shape and probably of the recticuloepithelial type. The small cells occurred in clumps mostly at the cortico-medullary junction, although single cells were found scattered in both the medulla and cortex. The large cell was restricted to the medulla and often was surrounded by the smaller cells. The antigen was not detected in frozen tissue sections from bursa, spleen or liver which suggests that the cells expressing the antigen are restricted to the thymus. Using the same antiserum, T1 was localized in thymus sections of other avian species. Soluble extracts prepared from the thymus of various avian and mammalian species were tested for T1 by immunoelectrophoresis (IE) and passive hemagglutination inhibition (HI) using anti-T1 serum. T1 was found in all avian species tested, but was not found in mammalian thymuses. The amount of T1 was quantitated in chickens of various ages by radial immunodiffusion (RID). The concentration of T1 increased linearly with age, and ranged from 32 micrograms/mg protein at 1 day of age to 45.6 micrograms/mg protein at 20 weeks of age. The total amount of T1 present reached maximal levels at 12 weeks of age and then declined during the period of thymus involution.