Infectious bursal disease virus (IBDV) capsids are formed by a single protein layer containing three polypeptides, pVP2, VP2, and VP3. Here, we show that the VP3 protein synthesized in insect cells, either after expression of the complete polyprotein or from a VP3 gene construct, is proteolytically degraded, leading to the accumulation of product lacking the 13 C-terminal residues. This finding led to identification of the VP3 oligomerization domain within a 24-amino-acid stretch near the C-terminal end of the polypeptide, partially overlapping the VP1 binding domain. Inactivation of the VP3 oligomerization domain, by either proteolysis or deletion of the polyprotein gene, abolishes viruslike particle formation. Formation of VP3-VP1 complexes in cells infected with a dual recombinant baculovirus simultaneously expressing the polyprotein and VP1 prevented VP3 proteolysis and led to efficient virus-like particle formation in insect cells.

Purpose: The histologic distinction between low-grade typical and intermediate-grade atypical bronchopulmonary carcinoids basically lies on cellular differentiation, mitotic activity, and presence of ''neoplastic'' necrosis; at single patient level, however, none of these features enables a reliable prediction of the clinicopathologic outcome. Experimental Design: The long-term postsurgical outcome of a single-institution series of 67 radically treated bronchopulmonary carcinoids was correlated with the tumor phenotype assessed by combining conventional histology with a panel of immunohistochemical markers exploring cell differentiation (chromogranin, NSE, TTF1), cell turnover (Mib1), and apoptosis (Bcl2, Bax). Results: Fifty-eight (86.6%) carcinoids were assessed as low-grade typical and nine (13.4%) were assessed as intermediate-grade atypical. The mean follow-up was of 85.13 months (range, 28-168; median, 82.0). All cases expressed neuroendocrine markers, whereas TTF1 was never expressed. At univariate analysis, tumor recurrence (n = 6) correlated significantly with the carcinoid histotype (P = 0.002) and with each of the following variables: tumor location (P = 0.01), mitotic index (P = 0.003), necrosis (P = 0.002), tumor vascular invasion (P = 0.0001), Mib1 expression (P = 0.005), Bcl2 expression (P = 0.024), and synchronous node metastasis (P = 0.028).The best cutoffs for Mib1and Bcl2 expression (calculated by receiver operating characteristic curves) discriminating recurrent versus nonrecurrent tumors were 5.4% for Mib1 and 2.0% for Bcl2 (Mib1: sensitivity, 83%; specificity, 97%; area under curve, 0.844 F 0.14; Bcl2: sensitivity, 83%; specificity, 65%; area under curve, 0.769 F 0.12). By stratifying the patients according to the obtained cutoffs, significant differences emerged in the patients' disease-free survival (log-rank test: Mib1, P = 0.0001; Bcl2, P = 0.01). Conclusions: Mib1 and Bcl2 significantly discriminate between recurrent versus nonrecurrent tumors, producing a biologically plausible, diagnostically suitable immunohistochemical pattern.

Infectious bursal disease virus (IBDV), a member of the

Borna disease virus (BDV) is an enveloped virus with a nonsegmented negative-strand RNA genome whose organization is characteristic of Mononegavirales. BDV cell entry follows a receptor-mediated endocytosis pathway, which is initiated by the recognition of an as-yet-unidentified receptor at the cell surface by the virus glycoprotein G. BDV G is synthesized as a precursor (GPC) that is cleaved by the cellular protease furin to produce the mature glycoproteins GP1 and GP2, which have been implicated in receptor recognition and pH-dependent fusion events, respectively. BDV is highly neurotropic and its spread in cultured cells proceeds in the absence of detectable extracellular virus or syncytium formation. BDV spread has been proposed to be strictly dependent on the expression and correct processing of BDV G. Here we present evidence that cell-to-cell spread of BDV required neither the expression of cellular receptors involved in virus primary infection, nor the furin-mediated processing of BDV G. We also show that in furin-deficient cells, the release of BDV particles induced by the treatment of BDV-infected cells with hypertonic buffer was not significantly affected, while virion infectivity was dramatically impaired, correlating with the decreased incorporation of BDV G species into viral particles. These findings support the view that the propagation of BDV within the central nervous systems of infected hosts involves both a primary infection that follows a receptor-mediated endocytosis pathway and a subsequent cell-to-cell spread that is independent of the expression of the primary receptor and does not require the processing of BDV G into GP1 and GP2.