Regional accumulation of Pgp-1+ memory cells in senescent mucosal immune system

The proportion of memory cells expressing the Pgp-1 surface marker, and subsets of T cells expressing L3T4 (CD4+ helper cells), Lyt-2 (CD8+ suppressor/cytotoxic cells), LFA-1 (lymphocyte function-associated antigen-1), and interleukin-2 receptors (IL-2R) on the cell surface in the spleen, regional lymph nodes (PLN), mesenteric LN (MLN), bronchial or mediastinal LN (BLN), Peyer's patches (PP), thymus, and bone marrow (BM) was studied in C57BL/6J mice of varying ages. Monoclonal antibodies (Mabs) IM7.8.1, FD4, GK1.5, 3.155, and FD441.8 were used to measure Pgp-1, IL-2R, L3T4 Lyt-2, and LFA-1 expressions, respectively. Optimal dose and kinetic studies were determined. The percentages of positive cells were determined by monoclonal antibody staining and flow cytometry or immunofluorescence microscopy. Using flow cytometric analysis, we found significant age-associated increases in the percentages of Pgp-1+ cells in the MLN as compared with a slight, but not significant, increase in the spleen. There were significant age-related increases in the percentages of Lyt-2+ cells in the spleen with no change in the MLN. The percentages of cells with the other phenotypic markers, L3T4, LFA-1, and IL-2R did not change with age in the spleen or MLN. Using immunofluorescence microscopy, the percentages of Thy-1.2+, Lyt-1+, and Lyt-2+ cells in different anatomical immune tissues did not change with age, except in the BLN and PP where there were significant age-related declines of the percentages of Thy-1.2+ and Lyt-2+ cells in the BLN, and of Lyt-1+ cells in the PP. These results indicate elevated levels of Pgp-1+ memory senescent cells in the MLN and these age-related shifts or changes in T lymphocyte subsets with age could contribute to the conserved immune responsiveness of senescent mucosal T lymphocytes.