Ontogenetic analysis of immune amplification by thymus-derived cells in chickens

The transfer of thymocytes from antigen-primed donors resulted in immune enhancement in recipients. When thymocytes from chicken donors primed with mouse erythrocytes were tested in hosts varying in age from 13 days of incubation to four days post-hatching, the immune enhancement effect was clearly host age dependent being negligible with 13-day embryo hosts and highest with four day chick hosts. When blood leucocytes or spleen cells from unprimed donors were tested in hosts of different ages a similar host age-dependent enhancement effect, but of lesser magnitude was observed. The amplification effect was even greater when the host embryos grafted with cells from unprimed donors were subjected to two MRBC injections at least three days apart, which indicated that these cells were sensitive to antigen priming. The enhancement capacity was minimal with cells from unprimed donors two weeks of age but increased as a function of age in older donors. These results are compatible with the hypothesis that a thymus-derived helper cell for antibody formation is being transferred and is responsible for the observed immune enhancement.