Tyrosine phosphorylation of a novel 100-kDa protein coupled to CD28 in resting human T cells is enhanced by a signal through TCR/CD3 complex.

For T cell activation, two signals are required, i.e., a T cell receptor (TCR)/CD3-mediated main signal and a CD28-mediated costimulatory signal. CD28 binds to its ligand (CD80 or CD86) and transduces the most important costimulatory signal. The cytoplasmic domain of the CD28 molecule, composed of 41 amino acids, does not contain any intrinsic enzyme activity. The cytoplasmic domain of CD28 is remarkably conserved among species and is associated with a number of signaling molecules that affect the main signal. We report here that a tyrosine phosphorylated 100-kDa protein (ppl00) was coupled to the CD28 cytoplasmic domain in Jurkat and human peripheral T cells. The pp100 was distinguished from other CD28 associated molecules such as Vav, STAT5, PI 3-kinase, Valosin-containing protein (VCP), Nucleolin, Gab2 (Grb2-associated binding protein 2), and STAT6. The tyrosine phosphorylation of pp100 coprecipitated with CD28 was enhanced by CD3 stimulation by the specific antibody, tyrosine phosphatase inhibitor and PKC activator. Tyrosine phosphorylation of pp100 was attenuated by the prior addition of PKC inhibitor. These findings indicate that pp100 is a novel tyrosine phosphorylated protein coupled to CD28 under continuous control of tyrosine phosphatases and might play a role in T cell activation augmented by a TCR/CD3-mediated main signal.

Decreased resistance to Listeria monocytogenes in mice following vanadate exposure: effects upon the function of macrophages.

We have previously demonstrated that ammonium metavanadate has a broad immunomodulating effect in mice after subchronic exposure. Because host resistance to pathogenic Listeria monocytogenes and in vitro phagocytic activity of harvested peritoneal macrophages (PEM) were strongly affected by vanadate treatment, we investigated the effect of vanadate on the functional role of resident PEM in active listeriosis in the mouse. Vanadium treatment results in altered patterns of clearance of the organism from the peritoneal cavity, liver and spleen. The total in vitro phagocytic uptake of Listeria by PEM was consistently decreased as a function of infection period. Similarly, intracellular killing of Listeria was decreased although the PEM from the vanadate-treated and control mice were more bacteriostatic than bactericidal. Population distributions of Listeria within infected PEM were not affected by host pretreatment with vanadate. Vanadate exposure interferes with both the uptake and ultimate intraphagolysosomal killing of Listeria. These results were expected in light of our previous studies of the effects of vanadate on PEM superoxide production, and hexose monophosphate shunt and glutathione redox cycle activity. The results provide additional information for the development of a mechanism to explain why workers exposed to vanadium-containing dusts have increased susceptibility to bacterial respiratory diseases.