Caveolae in the uptake and targeting of infectious agents and secreted toxins

A variety of microbial pathogens, including viruses, intracellular bacteria, and prions, as well as certain secreted bacterial toxins, can now be added to the list of ligands that enter cells via caveolae or caveolae-like membrane domains. In general, the caveolae-mediated entry pathway results in transport of these microbes and toxins to intracellular destinations that are different from that of cargo entering by other means. As a result, the caveolae-mediated entry pathway can profoundly affect the host cell-pathogen interaction long after entry has occurred. Furthermore, some microbes such as SV40 that enter via cavolae will be valuable as probes to analyze certain poorly understood intracellular trafficking pathways, such as retrograde transport to the ER. Also, viruses that enter via caveolae may have unique potential as gene and drug delivery vectors. In addition, some extracellular microbial pathogens, such as Pneumocystis carinii, may also interact with host cells via caveolae. Finally, caveolae may play a role in host immune defense mechanisms.

Association of caveolin with Chlamydia trachomatis inclusions at early and late stages of infection

The mechanism by which the intracellular bacterial pathogen Chlamydia trachomatis enters eukaryotic cells is poorly understood. There are conflicting reports of entry occurring by clathrin-dependent and clathrin-independent processes. We report here that C. trachomatis serovar K enters HEp-2 and HeLa 229 epithelial cells and J-774A.1 mouse macrophage/monocyte cells via caveolin-containing sphingolipid and cholesterol-enriched raft microdomains in the host cell plasma membranes. First, filipin and nystatin, drugs that specifically disrupt raft function by cholesterol chelation, each impaired entry of C. trachomatis serovar K. In control experiments, filipin did not impair entry of the same organism by an antibody-mediated opsonic process, nor did it impair entry of BSA-coated microspheres. Second, the chlamydia-containing endocytic vesicles specifically reacted with antisera against the caveolae marker protein caveolin. These vesicles are known to become the inclusions in which parasite replication occurs. They avoid fusion with lysosomes and instead traffic to the Golgi region, where they intercept Golgi-derived vesicles that recycle sphingolipids and cholesterol to the plasma membrane. We also report that late-stage C. trachomatis inclusions continue to display high levels of caveolin, which they likely acquire from the exocytic Golgi vesicles. We suggest that the atypical raft-mediated entry process may have important consequences for the host-pathogen interaction well after entry has occurred. These consequences include enabling the chlamydial vesicle to avoid acidification and fusion with lysosomes, to traffic to the Golgi region, and to intercept sphingolipid-containing vesicles from the Golgi.

Simian virus 40 infection via MHC class I molecules and caveolae

MHC class I molecules are a necessary component of the cell surface receptor for simian virus 40 (SV40). After binding to class I molecules, SV40 enters cells via a unique endocytic pathway that involves caveolae, rather than clathrin-coated pits. This pathway is dependent on a transmembrane signal that SV40 transmits from the cell surface. Furthermore, it delivers SV40 to the endoplasmic reticulum, rather than to the endosomal/lysosomal compartment, which is the usual target for endocytic traffic. The glycosphingolipid and cholesterol-enriched plasma membrane domains that contain caveolae are also enriched for class I molecules, relative to whole plasma membrane. Nevertheless, although class I molecules bind SV40, they do not enter with SV40, nor do they enter spontaneously into uninfected SV40 host cells. Instead, they are shed from the cell surface by the activity of a metalloprotease. These results imply the existence of a putative secondary receptor for SV40 that might mediate SV40 entry. It is not yet clear whether class I molecules are active in transmitting the SV40 signal. Monoclonal antibodies against class I molecules also induce a signal in the SV40 host cells. However, the antibody-induced signal is mediated by mitogen-activated protein kinase (MAP kinase), whereas the SV40 signal is independent of MAP kinase.

Extracellular simian virus 40 transmits a signal that promotes virus enclosure within caveolae

It was reported earlier that entry of simian virus 40 (SV40) into cells is promoted by a signal transmitted by the virus from the cell surface and that SV40 enters cells through caveolae. It is shown here that bound SV40 begins to partition into a caveolae-enriched Triton X-100-insoluble membrane fraction at 30 min postadsorption. Maximal levels of SV40 were seen in that fraction at 1 h. The sterol-binding agent nystatin, which selectively disrupts the cholesterol-enriched caveolae-containing membrane microdomain, selectively blocked the SV40-induced signal. This implies that the SV40 signal is transmitted from that membrane microdomain. The tyrosine kinase inhibitor genistein, which was earlier shown to block the SV40-induced signal and infectious entry, did not block the partitioning of SV40 into the detergent-insoluble membrane fraction. This shows that the signal is not required for the translocation of SV40 to the detergent-insoluble membrane and is consistent with the finding that the signal is likely transmitted from that membrane microdomain. However, electron microscopy of the Triton X-100-insoluble membrane fraction showed that genistein caused SV40 particles to accumulate at the annuli or mouths of the caveolae. In contrast, most SV40 particles were found enclosed within caveolae in parallel samples from untreated control cells. Together, these results imply that SV40 initially binds to flat detergent-soluble membrane. The virus then translocates to a caveolae-containing detergent-insoluble membrane microdomain. From the flat portion of that membrane microdomain the virus induces a signal which promotes its entry into caveolae.

MHC class I molecules are enriched in caveolae but do not enter with simian virus 40

Simian virus 40 (SV40) binds to MHC class I molecules anywhere on the cell surface and then enters through caveolae. The fate of class I molecules after SV40 binding is not known. Sensitivity of 125I-surface-labelled class I molecules to papain cleavage was used to distinguish internalized class I molecules from class I molecules remaining at the cell surface. Whereas the caveolae-enriched membrane microdomain was found to also be enriched for class I molecules, no internalized papain-resistant 125I-surface-labelled class I molecules could be detected at any time in either control cells or in cells preadsorbed with saturating amounts of SV40. Instead, 125I-surface-labelled class I molecules, as well as preadsorbed 125I-labelled anti-class I antibodies, accumulated in the medium, coincident with the turnover of class I molecules at the cell surface. The class I heavy chains that accumulated in the medium were truncated and their release was specifically prevented by the metalloprotease inhibitor 1,10-phenanthroline. Thus, whereas class I molecules mediate SV40 binding, they do not appear to mediate SV40 entry.

Bound simian virus 40 translocates to caveolin-enriched membrane domains, and its entry is inhibited by drugs that selectively disrupt caveolae

Simian virus 40 (SV40) entry leading to infection occurred only after the virus was at the cell surface for 1.5 to 2 h. SV40 infectious entry was not sensitive to cytosol acidification, a treatment that blocks endocytosis via clathrin-coated vesicles. Instead, SV40 infectious entry was blocked by treating cells with the phorbol ester PMA or nystatin, which selectively disrupts caveolae. In control experiments, transferrin internalization was sensitive to cytosol acidification but was not sensitive to PMA or nystatin. Also, absorbed transferrin entered cells within minutes. Finally, bound SV40 translocated to caveolin-enriched membrane complexes isolated by a Triton X-100 insolubility protocol. Treatment with nystatin did not impair SV40 binding but did block the partitioning of virus into the caveolin-enriched complexes.

Extracellular simian virus 40 induces an ERK/MAP kinase-independent signalling pathway that activates primary response genes and promotes virus entry

Simian virus 40 (SV40) binding to growth-arrested cells activated an intracellular signalling pathway that induced the up-regulation of the primary response genes c-myc, c-jun and c-sis within 30 min and of JE within 90 min. The up-regulation of the primary response genes occurred in the presence of cycloheximide and when UV-inactivated SV40 was adsorbed to cells. SV40 binding did not activate Raf or mitogen-activated protein kinase (MAP/ERK1), or mobilize intracellular Ca2+. The SV40-induced up-regulation of c-myc and c-jun was blocked by the tyrosine kinase inhibitor, genistein, and by the protein kinase C (PKC) inhibitor, calphostin C, but not by expression of the MAP kinase-specific phosphatase, MKP-1. These results suggest that the SV40-induced signalling pathway includes the activities of a tyrosine kinase and a Ca(2+)-independent isoform of PKC, but not of Raf or MAP kinase. Finally, SV40 infectious entry into cells was specifically and reversibly blocked by genistein.

Relationship between expression of epidermal growth factor and simian virus 40 T antigen in a line of transgenic mice

The pattern of expression of the simian virus 40 (SV40) T antigen gene and resultant dysplasia were re-examined in a line of transgenic mice in which the T antigen gene was under the control of the SV40 early promoter. We found that T antigen expression in the kidney, and resulting dysplastic lesions, occurred exclusively in the distal convoluted tubules and the ascending limbs of Henle. Epidermal growth factor (EGF) expression in the kidney of normal mice was similarly immunolocalized. The correlation between high EGF immunoreactivity in normal mouse tissues and T antigen expression in the transgenic counterpart was also seen in the choroid plexus epithelium and in the submandibular glands of male mice. T antigen was not found in the submandibular gland of transgenic females. Similarly, EGF was only rarely detected in the normal female submandibular gland. In contrast to the correlation between T antigen expression in the transgenic mice and EGF expression in the corresponding tissues of the normal mice, within the dysplastic lesions of the transgenic mice EGF expression was severely diminished. Adenocarcinomas of the male submandibular gland from another line of transgenic mice that expresses the Int-1 transgene, showed similarly reduced levels of immunostaining for EGF. Thus, reduced expression of EGF might be a general feature of dysplasia and tumorigenesis in those tissues that normally express EGF.

Virus receptors: implications for pathogenesis and the design of antiviral agents

A virus initiates infection by attaching to its specific receptor on the surface of a susceptible host cell. This prepares the way for the virus to enter the cell. Consequently, the expression of the receptor on specific cells and tissues of the host is a major determinant of the route of entry of the virus into the host and of the patterns of virus spread and pathogenesis in the host. This review emphasizes the virus-receptor interactions of human immunodeficiency virus, the rhinoviruses, the herpesviruses, and the coronaviruses. These interactions are often found to be complex and dynamic, involving multiple sites or factors on both the virus and the host cell. Also, the receptor may play an important role in virus entry per se in addition to its role in virus binding. In the cases of human immunodeficiency virus and the rhinoviruses, ingenious approaches to therapeutic strategies based on inhibiting virus attachment and entry are under development and in clinical trials.

Class I major histocompatibility proteins are an essential component of the simian virus 40 receptor

The class I molecules encoded by the major histocompatibility complex (MHC) present endogenously synthesized antigenic peptide fragments to cytotoxic T lymphocytes. We show here that these proteins are an essential component of the cell surface receptor for simian virus 40 (SV40). First, SV40 binding to cells can be blocked by two monoclonal antibodies against class I human lymphocyte antigen (HLA) proteins but not by monoclonal antibodies specific for other cell surface proteins. Second, SV40 does not bind to cells of two different human lymphoblastoid cell lines which do not express surface class I MHC proteins because of genetic defects in the beta 2-microglobulin gene in one line and in the HLA complex in the other. Transfection of these cell lines with cloned genes for beta 2-microglobulin and HLA-B8, respectively, restored expression of their surface class I MHC proteins and resulted in concomitant SV40 binding. Finally, SV40 binds to purified HLA proteins in vitro and selectively binds to class I MHC proteins in a cell surface extract.

Simian virus 40 DNA replication correlates with expression of a particular subclass of T antigen in a human glial cell line

Immunocytochemistry and in situ hybridization were used to identify simian virus 40 (SV40) large T-antigen expression and viral DNA replication in individual cells of infected semipermissive human cell lines. SV40 infection aborts before T-antigen expression in many cells of each of the human cell lines examined. In all but one of the human cell lines, most of the T-antigen-producing cells replicated viral DNA. However, in the A172 line of human glial cells only a small percentage of the T-antigen-expressing cells replicated viral DNA. Since different structural and functional classes of T antigen can be recognized with anti-T monoclonal antibodies, we examined infected A172 cells with a panel of 10 anti-T monoclonal antibodies to determine whether viral DNA replication might correlate with the expression of a particular epitope of T antigen. One anti-T monoclonal antibody, PAb 100, did specifically recognize that subset of A172 cells which replicated SV40 DNA. The percentage of PAb 100-reactive A172 cells was dramatically increased by the DNA synthesis inhibitors hydroxyurea and aphidicolin. Removal of the hydroxyurea was followed by an increase in the percentage of cells replicating viral DNA corresponding to the increased percentage reactive with PAb 100. The pattern of SV40 infection in A172 cells was not altered by infection with viable viral mutants containing lesions in the small t protein, the agnoprotein, or the enhancer region. Finally, in situ hybridization was used to show that the percentage of human cells expressing T antigen was similar to the percentage transcribing early SV40 mRNA. Thus, the block to T-antigen expression in human cells is at a stage prior to transcription of early SV40 mRNA.

Class I major histocompatibility proteins as cell surface receptors for simian virus 40

Class I major histocompatibility complex proteins appear to be the major cell surface receptors for simian virus 40 (SV40), as implied by the following observations. Adsorption of SV40 to LLC-MK2 rhesus monkey kidney cells specifically inhibited binding of a monoclonal antibody (MAb) against class I human lymphocyte antigen (HLA) proteins. Conversely, pretreatment of LLC-MK2 cells with anti-HLA MAbs inhibited infection by SV40. The ability of anti-HLA to inhibit infection was greatly reduced when the order of addition of the anti-HLA and the virus was reversed. Infection was also inhibited by preincubating SV40 with purified soluble class I protein. Finally, human lymphoblastoid cells of the Daudi line, which do not express class I major histocompatibility complex proteins, were infected at relatively low levels with SV40 virions. In a control experiment, we found that pretreatment of cells with a MAb specific for the leukocytic-function-associated antigen LFA-3 actually enhanced infection. This finding may also support the premise that class I major histocompatibility complex proteins are receptors for SV40.

SV40 DNA in a carrier system of human glioblastoma cells

The state of the SV40 DNA in a stable carrier system of A172 human glioblastoma cells was examined by Southern blot hybridization analysis. At a sensitivity of 0.1 viral genome equivalents per cell, we detected only free, apparently nondefective, viral genomes. However, when we overexposed our autoradiograms or examined cloned cell populations, integrated viral sequences were observed. Furthermore, aberrant forms of free viral DNA were seen as well. Four clones, isolated at 15 weeks, produced T antigen and displayed enhanced saturation density and plating efficiency characteristic of SV40 transformation. None of these clones produced capsid proteins or infectious virus, even upon fusion with CV-1 cells, Viral DNA in the clones ranged from 0.5 to 50 equivalents per cell, on the average. Two of the Week-15 clones contained a similar (but not identical) predominant truncated SV40 sequence which was present both in a free state and integrated at a single major site in a reiterated head-to-tail array. These clones also contained other minor integrated sequences. Another Week-15 clone contained viral sequences integrated at two major sites as well as heterogeneous free DNA. Only free aberrant DNA was detected in the fourth Week-15 clone. Seven of eight clones isolated at 23 weeks produced no infectious virus or T antigen. No viral DNA was detected in those clones. The eighth clone did produce infectious virus and contained a predominance of free viral DNA. All of the clones were susceptible to superinfection with wild-type SV40, although less so than uninfected A172 cultures.

Human glioblastoma cells persistently infected with simian virus 40 carry nondefective episomal viral DNA and acquire the transformed phenotype and numerous chromosomal abnormalities

A stable, persistent infection of A172 human glioblastoma cells with simian virus 40 (SV40) was readily established after infection at an input of 450 PFU per cell. Only 11% of the cells were initially susceptible to SV40, as shown by indirect immunofluorescent staining for the SV40 T antigen at 48 h. However, all cells produced T antigen by week 11. In contrast, viral capsid proteins were made in only about 1% of the cells in the established carrier system. Weekly viral yields ranged between 10(4) and 10(6) PFU/ml. Most of the capsid protein-producing cells contained enormous aberrant (lobulated or multiple) nuclei. Persistent viral DNA appeared in an episomal or "free" state exclusively in Southern blots and was indistinguishable from standard SV40 DNA by restriction analysis. Viral autointerference activity was not detected, and yield reduction assays did not indicate defective interfering particle activity, further implying that variant viruses were not a factor in this carrier system. Interferon was also not a factor in the system, as shown by direct challenge with vesicular stomatitis virus. Persistent infection resulted in cellular growth changes (enhanced saturation density and plating efficiency) characteristic of SV40 transformation. Persistent infection also led to an increased frequency of cytogenetic effects. These included sister chromatid exchanges, a variety of chromosomal abnormalities (ring chromosomes, acentric fragments, breaks, and gaps), and an increase in the chromosome number. Nevertheless, the persistently infected cells continued to display a bipolar glial cell-like morphology with extensive process extension and intercellular contacts.

Sequences locating the 5' ends of the major simian virus 40 late mRNA forms

The 5' sequences of late mRNA specified by several constructed or naturally occurring deletion or duplication mutants of simian virus 40 were examined. The mutants included viruses with various small deletions centered about 25 nucleotides upstream from the major transcription initiation site, as well as viruses containing tandem duplications of a sequence of 50 nucleotides or less embedding the major transcription initiation site. The results show that the sequences 25 to 30 nucleotides upstream from the major initiation site in the position of the TATA box of other polymerase II promoters are not essential for the precise localization of the initiation site of late mRNA. Rather, we deduce that the major late mRNA start site is determined primarily by sequences located very close to the initiation site, and that the relative abundance of the 5' ends with this initiation site is modulated by nearby downstream sequences. Modification of six nucleotides adjacent upstream to the initiation site almost completely prevents the utilization of this site. Various deletions and substitutions of sequences 21 nucleotides or more downstream from the major initiation site causes upstream shifts in the localization of the most abundantly utilized 5' ends. The sequences immediately downstream from the major simian virus 40 initiation sites contain inverted symmetries that could give rise to secondary structures in either single-stranded DNA or RNA; the possibility that these inverted symmetries function in transcription initiation at the level of DNA structure rather than in RNA stabilization is discussed. Finally, we present additional evidence that precursor species with certain 5' termini are selectively spliced to form 19S RNA, whereas other 5' termini are preferred for forming the 16S RNA splice. We discuss the possibility that this is a consequence of the influence of leader structure on downstream splicing events.

Recombinational joints in a simian virus 40 variant generated in a persistent infection

SP1, a viable simian virus 40 (SV40) variant isolated from a persistent infection of rhesus monkey kidney cells, contains sequence rearrangements in the untranslated region of the SV40 genome which are transcribed into late mRNA leader sequences and in the region which encodes the large T antigen. Nucleotide sequences about the recombinational junctions in SP1 were determined. The sequence data show that in most instances there was not extensive homology between recombining sequences. The recombinant sequences are discussed with respect to the mechanisms by which they might have been generated.

A viable simian virus 40 variant with a deletion in the overlapping genes for virion proteins VP1, VP2 and VP3

Nucleotide sequence analysis was used to determine the exact location of a deletion in the late region of the SP2 mutant of simian virus 40 (SV40), a viable small-plaque variant isolated from a persistent infection of rhesus monkey kidney cells. The results indicate that six base pairs are deleted from that part of the SV40 genome in which the coding regions for the three virion proteins, VP1, VP2 and VP3, overlap. This implies that all three virion proteins are affected by the deletion. This finding is discussed with respect to the viability of SP2.

Emergence of simian virus 40 variants during serial passage of plaque isolates

Three serial passage series of simian virus 40 (SV40) in CV-1 cells were initiated by infection directly from the same wild-type plaque isolate, three series were initiated by infection with another plaque isolate, and two series were initiated with each of two other plaque isolates. Aberrant SV40 genomes were not detected in any of the passage series until after the fifty undiluted passage, and each series generated a different array of variant genomes. The results show that the variants were not present in the original plaque isolates but, instead, were randomly generated during subsequent high-input multiplicity passages. Although many of the aberrant viral genomes in each passage series contained reiterations of the SV40 origin of replication and some also contained host cell sequences, there was no indication that SV40 is predisposed toward generating any particular variant.

Lysosome stability during lytic infection by simian virus 40

By 48 h postinfection, 40--80% of SV40-infected CV-1 cells have undergone irreversible injury as indicated by trypan blue staining. Nevertheless, at this time the lysosomes of these cells appear as discrete structures after vital staining with either acridine orange or neutral red. Lysosomes, vitally stained with neutral red at 24 h postinfection, were still intact in cells stained with trypan blue at 48 h. Acid phosphatase activity is localized in discrete cytoplasmic particles at 48 h, as indicated by histochemical staining of both fixed and unfixed cells.

Cell killing by Simian virus 40: protective effect of chloroquine

Treatment of CV-1 cells with chloroquine before infection by simian virus 40 resulted in the accumulation of fewer nonviable, trypan blue-stainable cells at 72 h. The drug did not affect the fraction of infected T-antigen-producing cells or the viral yields. It did diminish the apparent redistribution of lysosomal N-acetyl-beta-glucosaminidase from a particulate to a soluble cell fraction, and it caused an increase in the size and number of lysosomes.

Ribosomal proteins in normal simian cells, SV40-transformed simian cells, and simian cells infected with SV40, adenovirus 5, and vesicular stomatitis virus

The protein patterns of monosomes and polysomes isolated from the T-22 line of SV40-transformed GMK cells and from uninfected CV-1 cells and CV-1 cells infected with SV40, adenovirus 5, or vesicular stomatitis virus were analyzed by two-dimensional PAGE. All gel patterns were similar except for the presence of one additional protein associated with T-22 monosomes.

Effect of input multiplicity on the establishment of simian virus 40 persistent infections in rhesus monkey kidney cells

Monolayer cultures of LLC-MK2 rhesus monkey kidney cells become persistently infected with simian virus 40 after infection at input multiplicities of 100, 10, or 1 plaque-forming unit per cell. After 3 weeks, all cells of the cultures infected at a multiplicity of 1 plaque-forming unit per cell produced the simian virus 40 T antigen. In contrast, 8 to 11 weeks elapsed before all the cells in the cultures infected at a multiplicity of 100 plaque-forming units per cell produced T antigen. Defective interfering particles and interferon production were not evident during this time.

Cell killing by simian virus 40: impairment of membrane formation and function

Simian virus 40 infection of the CV-1 line of green monkey kidney cells results in the release of mitochondrial malic dehydrogenase as early as 24 h. Released malic dehydrogenase is detected in the cytoplasm prior to its appearance in the overlay medium. Infected cells lose the ability to consume oxygen between 48 and 56 h, and damage to the elctron transport system is indicated. Nevertheless, cellular ATP levels remain high as late as 72 h. Infection leads to a stimulation of membrane phospholipid synthesis, which reaches a peak at about 32 h. This is followed by a severe decline in new membrane synthesis, which correlates in time with the release of cytoplasmic lactic dehydrogenase into the overlay media. Lactic dehydrogenase release precedes the accumulation of trypan blue-stainable cells by about 6 h. Infection had no effect on the turnover of prelabeled membrane phospholipids. An early simian virus 40 mutant, tsA58, and a late mutant, tsB11, are both less effective than wild-type virus at causing reduced levels of phospholipid synthesis, enzyme release, and the accumulation of trypan blue-stainable cells. Another late mutant, tsB8, is similar to wild-type virus in these respects. At 64 h, there is no detectable cell-associated lactic dehydrogenase and nearly all the cells are trypan blue stainable. Nevertheless, at concentrations of deoxyglucose in the medium below the transport Km, deoxyglucose uptake was similar in infected and control cultures. With higher concentrations of deoxyglucose in the medium, uptake by the infected cultures exceeded that by the control cultures.

Rhesus monkeys kidney cells persistently infected with Simian Virus 40: production of defective interfering virus and acquisition of the transformed phenotype

Monolayer cultures of LLC-MK2 rhesus monkey kidney cells became persistently infected with simian virus 40 (SV40) when infected at a multiplicity of infection of 100 plaque-forming units/cell. A stable carrier state developed characterized by extensive viral proliferation without obvious cytopathic effect other than the slow growth of these cultures. By 11 weeks all cells produced the SV40 T antigen. In contrast, less than 5% of the cells produced V antigen. Virus-free clonal isolates were obtained by cloning in SV40 antiserum. Continuous cultivation in antiserum resulted in a temporary cure of unclone cultures. When virus did eventually reappear in the "cured" cultures the titers remained low. The virus produced by the carrier culture was defective at both 31 and 37% c, and it interfered with the growth of standard s40 during mixed infection of CV-1 green monkey kidney cells. All of the interfering activity in carrier culture homogenates could be sedimented by centrifugation at 109,000 x g for 3 h. These cultures were completely susceptible to vesicular stomatitis virus. Extensive viral deoxyribonucleic acid synthesis occurred in CV-1 cells infected with carrier culture virus. Carrier culture homogenates are only slightly less cytopathic to CV-1 cells than standard SV40. The carrier culture express several properties of SV40 transformation.

Cell killing by simian virus 40: variation in the pattern of lysosomal enzyme release, cellular enzyme release, and cell death during productive infection of normal and simian virus 40-transformed simian cell lines

Simian virus 40 (SV40) growth on rhesus kidney cells and on the T-22 line of SV40-transformed green monkey kidney (GMK) cells is largely limited by the low plating efficiency of SV40 on these cells. In addition, a fraction of the rhesus kidney and T-22 cells are resistant to infection by SV40. Nevertheless, 72-h viral yields per infected rhesus kidney and T-22 cell are nearly equivalent to that obtained on normal GMK cells and are independent of the multiplicity of infection. Despite the production of high viral yields, infected rhesus kidney and T-22 cells are killed slowly by SV40. Monolayers of these cells are also refractory to plaque formation by SV40. SV40 induces the release of lysosomal N-acetyl-beta-glucosaminidase into the cytoplasmic fractions of rhesus kidney and T-22 cells to an extent equal to that observed during infection of rapidly killed normal GMK cells. In contrast, damage to the plasma membrane, as indicated by the release of the cellular enzymes lactic dehydrogenase and glutamic oxaloacetic transaminase into the overlay media, occurred to a much greater extent in the normal GMK cells than in the rhesus kidney or T-22 cells. Neither a lysosomal hydrolase mechanism nor viral release appear to be responsible for this phenomenon. The different rates and extents of the SV40 cytocidal process on these cells do not result from the differences in the viral plating efficiency on them.