Age influence on the thymic capacity to promote differentiation of T cells: induction of different composition of T cell subsets by aging thymus.
Three kinds of experiments were performed to see the differential effect of aging thymus on T cell differentiation in nude mice and thymectomized mice. In the experiment of thymus grafting into nude mice, the thymic capacity to promote T cell differentiation was the highest at newborn stage, and declined to 80% of the peak level at as early as 1 week of age. The level at 4 weeks of age was 50-60% of the peak level and did not greatly change thereafter with advancing age of thymus donors, up to 24 months of age. However, composition of T cell subsets differed with age of thymus graft; i.e. L3T4(CD4)+ T cells were more easily induced than Lyt-2(CD8)+ T cells by aging thymus, resulting in an increase of the ratio of L3T4+/Lyt-2+ T cells with advancing age of thymus donors. The decreased number of T cells and their subsets in the mice thymectomized at 4 weeks of age could be almost totally recovered by the grafting of newborn thymus, but less efficiently by the grafting of 24-month-old thymus. In the latter case again, L3T4+ T cells were more easily induced than Lyt-2+ T cells, resulting in an increase of the ratio of L3T4+/Lyt-2+ T cells by the grafting of the old thymus. In neonatal mice thymectomized 3 days after the birth, Lyt-2+ T cells were more severely affected than L3T4+ cells, resulting in high ratio of L3T4+/Lyt-2+ T cells. It was suggested that the capacity of the thymus to induce T cells started to decline as early as 1 week of age and did not greatly change between 4 weeks and 24 months of age. However, the composition of T cell subsets induced by the thymus changed with age, with preference for L3T4+ T cells over Lyt-2+ T cells.
Utsuyama
M
M
Department of Immunopathology, Tokyo Metropolitan Institute of Gerontology, Japan.
Kasai
M
M
Kurashima
C
C
Hirokawa
K
K
D000375:Aging / Q000276:immunology*; D000818:Animals; D000917:Antibody Formation; D002454:Cell Differentiation; D005260:Female; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008819:Mice, Nude; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology*; D013934:Thymectomy; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology / Q000637:transplantation