Isopycnic centrifugation of rhinovirus type 14 (RV14), purified from infected HeLa or KB cell cultures, into CsCl gradients resolved two bands of infectious virus particles with buoyant density values of 1.409 +/- 0.007 (H virus) and 1.386 +/- 0.004 (L virus) g/ml. Only H virus was detected by incorporation of radiolabeled uridine into viral RNA, and H virus accounted for the majority of infectivity in gradients. H and L virus could not be differentiated by plaque morphology, extent of neutralization by RV14-specific antiserum, or particle size. Electron microscope studies showed that most L-virus particles were associated with an amorphous material. Treatment of L virus with proteolytic enzymes or rebanding L virus in CsCl gradients resulted in recovery of the majority of infectivity as H virus. Virus purified from cell-free fluids from infected HeLa or KB cell cultures banded only as H virus. HeLa cell cultures challenged with purified H virus and harvested at 3 h postinoculation for virus purification yielded only infectious H virus. Both H and L viruses were detected in cell cultures that had been challenged with purified H virus and harvested at 12 h postinoculation. The data suggest that H virus represents progeny virus, whereas L virus represents sequestered infectious virus particles which become associated with an amorphous material and do not enter into viral replicative processes.

The rhinoviruses, a subgroup within the pieornaviruses, currently consist of 89 different serotypes (8). A number of differences in biological properties have been reported for the few rhinovirus serotypes studied (see review, 10), however, additional data are needed to warrant continued classification of this large a group of viruses within one subgroup. In this study, we describe some biological characteristics of the growth of rhinovirus type 14 (RV 14) in IteL~ and KB cell cultures.Methods for the propagation and assay of RV14 and for the culture and preparation of KB and HeLa cells for experiments were previously described (9). Zero time in all studies was regarded as the instant of addition of virus to cell cultures.l~ates of adsorption of RV14 to KB and HeLa monolayer cell cultures at 34.5~ C were measured by determining the amount of virus remMning in an inoeulum after challenge of cells with 10 plaque-forming units (PFU)/cell in 0.2 ml. Virus adsorption to KB cell cultures was greater (55 per cent) than to HeLa cell cultures (36 per cent) within the initial 30 minute period. Thereafter, similar rates of adsorption occurred to either cell culture and adsorption was approximately linear for the next 90 minutes, resulting in adsorption of 95 and 79 per cent of virus to KB and HeLa cell cultures, respectively. In published studies, only 30 to 35 per cent of t~V 14 adsorbed to tteLa cells in suspension culture and adsorption was essentially complete by 30 minutes post inoculation (p.i.) (6, 11). Under comparable conditions, rhinovirus type 2 (RV2) attached at a-rate which was 20 to 40 times greater than that of RV 14 (6).The time course of production of infectious RV 14 in KB and HeLa cell cultures following challenge with 20 to 25 PFU/eell is shown in Fig. 1. The growth cycle of I~V 14 in KB cells required only two-thirds as much time as a complete growth cycle in HeLa cells. Eclipse and rise periods in KB cells were 1 and 2 to 3 hours shorter, respectively, than similar periods in infected HeLa cells: Approximately 1 per cent and between 5 and 8 per cent of infectious virus were released as free