Immunocytochemical Localization of Phospholipase C Isozymes in Cord Blood and Adult T-lymphocytes

SUMMARY The response of T-cells to peptide antigen plus major histocompatibility complex (MHC) consists of a series of cellular events collectively called T-cell activation. An essential component of this pathway is phospholipase C (PLC) g 1, whose hydrolytic activity increases rapidly after binding of ligands to the T-cell receptor (TCR) and consequent activation of tyrosine kinases. Recent studies also suggest a GTP binding protein-dependent activation of PLC b during the early steps of T-cell activation. On the basis of these findings, we first checked the expression of PLC isoforms by Western blotting and by confocal and electron microscopy techniques, and then we looked for the phosphoinositide breakdown induced by CD3 engagement in cord and adult T-lymphocytes. Our results indicated that PLC b 1 was almost exclusively expressed in cord T-cells, whereas PLC b 2 was more strongly represented in the adult. The amount of PLC g 1 was found to be larger in the adult than in cord cells. No significant differences were found in PLC g 2 and d 2 expression. PLC d 1 was scarcely detectable. On CD3 stimulation, adult lymphocytes gave rise, as expected, to a dramatic increase in phosphoinositide breakdown, whereas in cord cells this response was scarcely detected. These results indicate that a shift in PLC expression occurs in the postnatal period and that this change is associated with induction of the capability to respond to CD3 engagement with phosphoinositide hydrolysis. (J Histochem Cytochem 47:929‐935, 1999)