Selective deficiency in protein kinase C isoenzyme expression and inadequacy in mitogen-activated protein kinase activation in cord blood T cells.

The biochemical basis for the reduced lymphokine production by neonatal T cells compared with adult T cells remains poorly defined. Previous studies have raised the possibility that neonatal T cells could be deficient in their ability to transmit signals via protein kinase (PK) C. We now report that while PKC-dependent activation of the mitogen-activated protein (MAP) kinases, c-Jun N-terminal protein kinase and the extracellular signal-regulated protein kinase (ERK)1/ERK2, was deficient in cord blood T cells compared with adult blood T cells, marked activation of the MAP kinases in cord blood T cells was achieved via PKC-independent means. Consistent with a deficiency in the signalling capability of PKC, cord blood T cells were selectively deficient in the expression of PKC beta I, epsilon, theta and zeta. Stimulation of cord blood T cells resulted in a time-dependent increase in PKC expression, with increases detectable by 4 h. This was accompanied by an enhancement in MAP kinase activation via PKC-dependent means. These novel data suggest that an inadequacy in PKC-MAP kinase signalling may be responsible, at least in part, for the phenotype of cord blood T cells.