Entry of simian virus 40 is restricted to apical surfaces of polarized epithelial cells.

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Abstract
The uptake of simian virus 40 (SV40) by polarized epithelial cells was investigated by growth of cells on permeable supports and inoculation on either the apical or the basolateral surface. Binding of radiolabeled SV40 occurred on the apical but not the basolateral surfaces of permissive polarized Vero C1008 cells and nonpermissive polarized MDCK cells. When similar experiments were performed on nonpolarized Vero or CV-1 cells, virus binding occurred regardless of the direction of virus input. Electron micrographs of Vero C1008 cells infected at high multiplicities revealed virions lining the surfaces of apically infected cells, while the surfaces of basolaterally infected cells were devoid of virus particles. Analysis of the binding data revealed a single class of virus receptors (9 x 10(4) per cell) with a high affinity for SV40 (Kd = 3.76 pM) on the apical surfaces of Vero C 1008 cells. Indirect immunofluorescence studies revealed that synthesis of viral capsid proteins in Vero C1008 cells occurred only when input virions had access to the apical surface. Virus yields from apically infected Vero C1008 cells were 10(5) PFU per cell, while yields obtained from basolaterally infected cells were less than one PFU per cell. These results indicate that a specific receptor for SV40 is expressed exclusively on the apical surfaces of polarized Vero C1008 cells.