PERIPHERAL-BLOOD CD4(-LINEAGE()CD8(+) LYMPHOCYTES IN CYNOMOLGUS MONKEYS ARE OF RESTING MEMORY T)

In this study, we analyzed peripheral blood CD4(+)CD8(+) double-positi ve (DP) lymphocytes in adult cynomolgus monkeys (Macaca fascicularis). Forty of 55 monkeys had >5% of the peripheral blood DP subpopulation (9.3 +/- 5.9%; mean +/- SD) in peripheral blood lymphocytes (PBL) in c ontrast to a low percentage of peripheral blood DP cells in humans and mice. In a cross-sectional study, the peripheral blood DP cells were found to increase in proportion with age. To clarify whether periphera l blood DP lymphocytes were immature precursors released from thymus w ithout prior differentiation, the expressions of CD8 chains and CD1b o n peripheral blood DP lymphocytes were compared with those on thymocyt es. The peripheral blood DP lymphocytes were CD8 alpha(+)beta(-) and C D1b(-), while thymic DP lymphocytes were CD8 alpha(+)beta(+) and CD1b( +), suggesting that the peripheral blood DP cells are extrathymic T ly mphocytes. Furthermore, the peripheral blood DP lymphocytes exhibited a resting memory T cell phenotype with (hi)CD3(+)CD28(-)CD29(hi)CD49d( hi)CD69(-)CD80(lo). Taken together, adult cynomolgus monkeys possess a unique peripheral blood DP T cell subpopulation which expresses a res ting memory T cell phenotype. In addition, similar phenotypic properti es of DP lymphocytes were distributed in the spleen and lymph nodes, a lthough the proportion was less in the spleen and much less in lymph n odes than in PBL.