Actin is a component of the compensation mechanism in pseudorabies virus virions lacking the major tegument protein VP22.

Despite being a major component of the pseudorabies virus tegument, VP22 is not required for PRV replication, virulence, or neuroinvasion (T. del Rio, H. C. Werner, and L. W. Enquist, J. Virol. 76:774-782, 2002). In the absence of VP22, tegument assembly compensates in a limited fashion with increased incorporation of cellular actin. Infection of epithelial cell lines expressing fluorescent actin fusion proteins resulted in the incorporation of filamentous and nonfilamentous actin into individual virions that were predominately light, noninfectious particles. We conclude that cellular actin is incorporated in the tegument of wild-type virions and is part of a compensation mechanism for VP22-null virions.

Mechanisms underlying reduced responsiveness of neonatal neutrophils to distinct chemoattractants.

Potential mechanisms underlying impaired chemotactic responsiveness of neonatal neutrophils were investigated. Two distinct chemoattractants were compared: bacterially derived N-formyl-methionyl-leucyl-phenylalanine (fMLP) and a unique chemotactic monoclonal antibody, designated DL1.2, which binds to a neutrophil antigen with an apparent molecular mass of 120 kDa. Chemotaxis of neutrophils toward fMLP, as well as DL1.2, was reduced in neonates when compared with adult cells. This did not appear to be a result of decreased fMLP receptor or DL1.2 antigen expression by neonatal neutrophils. fMLP, but not DL1.2, induced a rapid increase in intracellular calcium in adult and neonatal cells, which reached a maximum within 30 s. The calcium response of cells from neonates to fMLP was reduced when compared with adult cells, and an unresponsive subpopulation of neonatal neutrophils was identified. NF-kappaB nuclear binding activity induced by fMLP and DL1.2, as well as expression of the p65 NF-kappaB subunit and IkappaB-alpha, was also significantly reduced in neonatal cells, when compared with adult cells. In contrast, although fMLP, but not DL1.2, activated p42/44 and p38 mitogen-activated protein (MAP) kinases in neutrophils, no differences were observed between adults and neonates. Chemotaxis of adult and neonatal neutrophils toward fMLP and DL1.2 was also blocked to a similar extent by inhibitors of phosphatidylinositol 3-kinase, as well as an inhibitor of NF-kappaB. These findings indicate that reduced chemotactic responsiveness in neonatal neutrophils is a result of, at least in part, aberrations in chemoattractant-induced signaling. However, the biochemical pathways mediating this defect appear to be related to the specific chemoattractant.

Effects of cadmium on metallothionein levels in human peripheral blood leukocytes: a comparison with zinc.

Metallothioneins (MT) are low-molecular-weight, cysteine-rich proteins that are induced in response to a variety of chemical stresses and therefore can be used to assess human exposure to environmental agents. In the current study, flow cytometry was used to characterize the basal and cadmium-induced expression of MT in the three major leukocyte populations of human peripheral blood. In the analysis, monocytes were the most sensitive leukocytes to this toxic metal, with significant increases in cellular MT levels being detected at concentrations of cadmium as low as 0.1 microM (24 h). The lymphocyte population also exhibited pronounced treatment-associated elevations in cellular MT, while the granulocyte population was found to be nonresponsive. Although both CdCl2 (3 microM) and ZnCl2 (50 microM) induced MT expression in monocytes to a similar degree and did not affect the expression of this protein in granulocytes, cadmium but not zinc treatment induced dramatic increases in MT levels of lymphocytes. Our results indicate that cellular MT protein levels, as determined by this flow cytometric method, may be used to characterize the differential responsiveness of the major human leukocyte subpopulations to transitional metals. It is evident from the current work that the responsiveness of all peripheral blood leukocyte populations should be analyzed in exposure assessment studies.