PATTERNS OF RESPONSIVENESS OF T-CELL LINES AND THYMOCYTES REVEAL WAVES OF SPECIFIC ACTIVITY IN THE POSTNATAL MURINE THYMUS

Antibody binding of CD3, CD4, or CD8 molecules can induce cytoplasmic calcium mobilization in T lymphocytes, usually interpreted as indicating signal transduction. Using such assays, in a CD4+CD8+ thymocyte line and its single positive progeny we have identified characteristic patterns of responsiveness that are reproducible in vivo in a subpopulation of newborn 'double positive' thymocytes but virtually absent in adult thymuses. In particular, these cells appear to be high responders to the binding of anti-CD3 F(ab)'2 fragments. We have followed the presence of such highly responsive thymocytes in the perinatal period and the first 15 days of life. Intriguingly, these cells populate the newborn thymus in three distinct waves. Such patterns of responsiveness may define early 'selectable' thymocytes.