Immunocytochemical localization of phospholipase C isozymes in cord blood and adult T-lymphocytes

The response of T-cells to peptide antigen plus major histocompatibility co mplex (MHC) consists of a series of cellular events collectively called T-c ell activation. An essential component of this pathway is phospholipase C ( PLC)gamma 1, whose hydrolytic activity increases rapidly after binding of l igands to the T-cell receptor (TCR) and consequent activation of tyrosine k inases. Recent studies also suggest a GTP binding protein-dependent activat ion of PLC beta during the early steps of T-cell activation. On the basis o f these findings, we first checked the expression of PLC isoforms by Wester n 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 beta 1 was almost exclusively expressed in cord T-cells, whereas PLC beta 2 was more strongly represented in the adult. The amount of PLC gamma 1 was found to be larger in the adult than in cord cells. No significant differences were found in PLC gamma 2 and delta 2 expression. PLC delta 1 was scarcely detectable. On CD3 stimulation, adult lymphocytes gave rise, as expected, to a dramatic i ncrease in phosphoinositide breakdown, whereas in cord cells this response was scarcely detected. These results indicate that a shift in PLC expressio n occurs in the postnatal period and that this change is associated with in duction of the capability to respond to CD3 engagement with phosphoinositid e hydrolysis.