Age-associated increase in the expression of T-cell antigen receptor γ-chain gene in conventional and germfree mice

To determine whether environmental antigens such as intestinal microflora contribute to expansion of the T-cell repertoire, age-related changes in the expression level of T-cell antigen receptor genes encoding γ, β, and α chains were compared in the lymphoid tissues of conventional versus germfree mice. Irrespective of the conditions of maintenance, an age-associated increase in the expression of the γ-chain gene was evident in the thymus and spleen. Both conventional and germfree old mice (age, 40 weeks) had a relatively high proportion of Thy1⁺ L3T4^- Lyt2^- cells but a reduced level of Thy1⁺ L3T4^- Lyt2⁺ cells in the thymus compared with their counterparts (age 8 weeks). The thymic dysfunction but not the stimulation by intestinal microflora may contribute to this age-related increase in γ-gene transcripts in these tissues. On the other hand, an age-associated increase in the expression of γ RNA was not evident in the mesenteric lymph nodes of germfree mice, although a remarkable increase in the γ-chain gene messages was detected in the lymph nodes of the aged conventional mice. These results suggest that the expression of γ RNA in cells of gut-associated lymphoid tissue is partly influenced by intestinal microflora.