Age-related changes of naive and memory CD4 rat lymphocyte subsets in mucosal and systemic lymphoid organs

The purpose of this study was to investigate in rats, by double-label immunofluorescence and flow cytometric analysis, the age related changes in the CD4 subset of gut-associated lymphoid tissues and spleen. We found that the percentage of CD4+ T cells in Peyer's patches (PP) and spleen (SP) increased during the first 6 weeks after weaning. An age-related decrease of the CD4 subset was observed in SP of aged rats, but not in their PP. In all lymphoid tissues studied, an age-related decrease of the Thy-1+ subset was observed from weaning to 2 years of age. Analysis of the naive CD4 subset (CD45RC+) showed that in SP this subset increased during the first 9 weeks of age, and declined in aged rats. However, in PP this subset presented a slow decrease from weaning until 2 years of age. Together with the decrease of the naive subset, a sharp increase of the memory/activated CD4+ cells (CD45RC- Thy-1-) was observed in PP, and to a lesser extent in SP. When the maturation of the CD4 T cells in PP was followed during the first week after weaning, we found that an important proportion of this subset changes its phenotype at this time, from recent thymic emigrant (CD45RC- Thy-1+) to naive T cell (CD45RC+ Thy-1-) and then to activated/memory cell (CD45RC- Thy-1-). Therefore it appeared that CD4 T cells from PP mature faster than SP CD4 T cells, and they are not subject to the deleterious effect of aging. One surprising point was the different kinetics of the CD4 T cells observed in mesenteric lymph nodes (MLN). No age-related changes were observed in the CD4 subset at this site. Furthermore, the percentage of the CD45RC+ cells did not decrease in aged rats, and in the first 9 weeks of life an increase of this subset was observed.