Abstract
Summary
Addition of CT to suspensions of thymus, lymph node, spleen, or bone marrow cells in vitro resulted in a marked accumulation of cAMP with peak levels occurring 4-5 hr after incubation of cells with CT. Thymus cells showed the largest increase in cAMP, approximately 40-fold at 10 ng/ml CT. Bone marrow cells accumulated the least cAMP (1.5x), while intermediate levels were observed for spleen and lymph node cells (10-12x). Antiserum to CT prevented stimulation of increased cAMP levels.
Repopulation studies using X-irradiated mice also showed that thymus-derived spleen cells accumulated more cAMP/107 cells than spleen cells from recipients given spleen or marrow cells. Spleen cells from athymic (nu/nu) mice also responded much less than did spleen cells from normal mice.
Thymocytes appeared to bind CT to a greater degree than bone marrow cells. Spleen and lymph node cell suspensions also contained CT-binding cells and the number of CT-binding cells in these peripheral lym-phoid tissues appeared approximately equal to the summation of the numbers observed in thymocyte and bone marrow cell suspensions.
Stimulation of cAMP in lymphoid cells, especially thymocytes, by CT provides a pharmacological tool to investigate the mechanism and role of this nucleotide in the early events of antibody formation.
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