Studies on thymus products. V. Influence of genetic selection based on antibody production on thymus hormone production.

Outbred Swiss mice show a stable level of circulating thymic factor (TF) (measured by its action on theta-positive rosette-forming cells (RFC) until the 6th month of life. Afterwards, this level progressively declines. Swiss mice genetically selected as high' and low' responders for anti-sheep red blood cell haemagglutinin production show no difference with ordinary Swiss mice with regard to serum TF level. This observation is compatible with previous results showing that the selection mainly induces changes in B-cell reactivity without T-cell modification. Conversely, genetic selection of Swiss mice based on spontaneous antinuclear autoantibody production (tested by immunofluorescence) induces a decrease in TF level, which has already become significant by 2 months of life. The mice thus selected (Swan mice) which present autoimmune manifestations and immune complex disease, like NZB and B/W mice, show the same premature cessation of TF as these other autoimmune mice. Such abnormality is compatible with the T-cell deficiency of NZB, B/W and Swan mice.