Cell-mediated immune reaction against BK virus-transformed cells

Infection of vero cells by BK virus is dependent on caveolae

Polyomavirus-associated nephropathy occurs in approximately 5% of renal transplant recipients and results in loss of graft function in 50 to 70% of these patients. The disease is caused by reactivation of the common human polyomavirus BK (BKV) in the transplanted kidney. The early events in productive BKV infection are unknown. In this report, we focus on elucidating the mechanisms of BKV internalization in its target cell. Our data reveal that BKV entry into permissive Vero cells is slow, is independent of clathrin-coated-pit assembly, is dependent on an intact caveolin-1 scaffolding domain, is sensitive to tyrosine kinase inhibition, and requires cholesterol. BKV colocalizes with the caveola-mediated endocytic marker cholera toxin subunit B but not with the clathrin-dependent endocytic marker transferrin. In addition, BKV infectious entry is sensitive to elevation in intracellular pH. These findings indicate that BKV entry into Vero cells occurs by caveola-mediated endocytosis involving a pH-dependent step.

Differential distribution of the JC virus receptor-type sialic acid in normal human tissues

JC virus (JCV), a member of the polyomavirus family, causes a demyelinating disease of the central nervous system (CNS) in humans known as progressive multifocal leukoencephalopathy. Although glial cells are the principal target of JCV productive infection in progressive multifocal leukoencephalopathy patients, little is known regarding the site of JCV persistence and the mechanisms by which the virus spreads to the CNS to cause disease. Previous work has demonstrated the presence of replicating JCV DNA in B lymphocytes from peripheral blood, tonsil, and spleen and it has been hypothesized that lymphocytes may be one site of JCV persistence. Detection of viral gene products in renal tubules and excretion of JC virions in the urine suggests JCV persistence in the kidney. A respiratory route of viral transmission has also been hypothesized implicating the lung as another possible site of persistent JCV infection. Earlier studies from our laboratory have shown that terminal alpha 2,6-linked sialic acid is a critical component of the JCV receptor. In this report we examined the tissue distribution of this JCV receptor-type sialic acid in a panel of normal human tissues. Our results demonstrate that in normal brain JCV receptor-type sialic acids are expressed on oligodendrocytes and astrocytes, but not on cortical neurons. The receptor-type sialic acid is also more highly expressed on B lymphocytes than on T lymphocytes in normal human spleen and tonsil. In addition, both the kidney and lung express abundant levels of alpha 2-6-linked sialic acids. Our data show a striking correlation between the expression of the JCV receptor-type sialic acid on cells and their susceptibility to infection by the virus. These findings also support the hypothesis of JCV persistence in lymphoid tissue and B-cell-facilitated viral dissemination to the CNS.

Local immune reaction in syngeneic mice against tumorigenic and nontumorigenic BPV-transformed mouse cell lines

The role of cytotoxic T cells in immune response to Bovine Papillomavirus type 1 (BPV1)-transformed mouse cell lines was assessed. The chromium release assay was used to follow the induction of cytotoxicity in local lymph nodes of syngeneic C57BL/6J (B6) mice after injection of BPV1-transformed cell lines tumorigenic in nude mice but tumorigenic or nontumorigenic in B6 mice. The nontumorigenic cell line B6B31.C-NuT.A induced cell line-specific cytotoxicity with a maximal activity on day 7 after subcutaneous inoculation of one million B6B31.C-NuT.A cells. After injection of nontumorigenic B6B31.J or tumorigenic B6B31.J-NuT.A or B6B31.A cell lines, only low levels of nonspecific cytotoxicity were observed. These results suggest a role for cytotoxic T cells only in rejection of B6B31.C-NuT.A cells. One reason for the poor immunogenicity could be the lack of transformation-induced/virus-specific antigens on most of the present BPV1-transformed cell lines. However, in a transplantation rejection experiment, protection was induced in B6 mice against a challenge of the highly tumorigenic B6B31.A-B6T.1 line by repeated injections of BPV1-transformed cells. These results suggest the expression of common transplantation rejection antigens on the three BPV1-transformed cell lines used in the immunization experiments.

Generation of cell-mediated cytotoxicity against bovine-papilloma-virus-transformed primary mouse cell lines

The immunogenicity and immunosensitivity of primary mouse cell lines transformed by bovine papilloma virus 1 (BPV1) DNA were studied in a syngeneic mouse model by determining cell-mediated cytotoxicity in the spleens of mice immunized with the transformed cells. One of the cell lines induced the generation of cell-line-specific Thy1.2-positive cytotoxic effector cells. However, most of the cell lines tested induced the generation of Thy1.2-positive effector cells, which in addition to BPV1-transformed cells were able to lyse a syngeneic cell line transformed by methylcholanthrene. The lysis of BPV1- and methylcholanthrene-transformed cell lines was mediated by recognition of the same antigenic determinants expressed on these cells, and all the BPV1-transformed cell lines were sensitive to lysis by these nonspecific effector cells of the lymphokine-activated killer (LAK) type.

Correlation between tumour antigens and malignancy in BKV-transformed hamster cells

Hamster kidney cells transformed by BK virus (HKBK cells) were studied in order to correlate the membrane tumour antigens to the metastatic capability. The presence of the tumour associated surface antigen (TASA) on the surface of HKBK cells was detected by the immunofluorescence test on live cell suspensions. The metastatic ability was investigated by inoculating HKBK cells subcutaneously (s.c.) into newborn hamsters, s.c., intraperitoneally (i.p.) and in the foot pads into adult hamsters, and s.c. into adult hamsters previously immunized with surface antigens extracted from HKBK cells. The results indicate that there is a correlation between the appearance of tumour antigens on the cell surface and the metastatic ability: HKBK cells at low passage (about 30 subcultures after transformation) showed the capping of TASA in the cell membrane and low metastatic ability, whereas HKBK cells at high passage (about 130 subcultures after transformation) exhibited a diffuse appearance of TASA in the cell surface and were highly metastatic.

Phenotypic transformation of primary mouse fibroblasts by BPV 1 DNA

Cultures of primary fibroblasts of C57BL/6J mice were used as targets for transformation by bovine papillomavirus type 1 (BPV 1) DNA. Although no foci were observed, several lines of transformed cells were established by subculturing. These immortalized cell lines had in vitro growth characteristics in high and low serum media and saturation densities typical of transformed cells. Karyotype analyses revealed extensive aneuploidic changes. In two of the three cell lines analyzed, viral DNA was present in monomeric episomal form, in the third cell line all viral sequences were found in the high molecular weight region of a Southern blot. Despite the transformed phenotype, only one of the cell lines was tumorigenic in nude mice at a low level.

Tumour-associated antigens in primary mouse fibroblasts induced by transformation with bovine papillomavirus type 1

Bovine papillomavirus type 1 (BPV 1) DNA was used to transform primary fibroblasts of C57BL/6J mice. Transformation frequency in these cells was much lower than in C127 cells and not associated with the appearance of morphologically distinct foci. However, continuous lines of transformed C57BL/6J cells were developed by serial subculturing of transfected cells. These transformed cell lines showed phenotypic properties associated with transformation including abnormal karyotypes. They contained variable amounts of viral DNA, but the copy number was in the same range as in six C127 transformants tested for comparison. In two cell lines monomeric viral DNA in an episomal form was detected. Slowly migrating viral sequences in these and in the third line were probably episomal concatamers, but the possibility of integration could not be excluded. There was some variation in immunogenicity, but all cell lines induced a cell-mediated immune response in syngeneic mice detected by the chromium release assay. In addition to BPV 1-transformed cell lines, the effector cells also reacted against an unidentified antigen shared by 2 cell lines transformed by SV40 and UV irradiation, respectively.