title: The location in cartilage of infectious retrovirus in cats infected with feline leukemia virus.
abstract: BACKGROUND
  Previous studies have suggested that articular cartilage allografts were not likely to transmit infectious retrovirus since viral DNA could not be isolated from chondrocytes of infected individuals. However, the ability of the extracellular matrix of articular cartilage to harbor and transmit a retrovirus has not been examined. We hypothesized that articular cartilage fragments, but not isolated chondrocytes, from cats systemically infected with feline leukemia virus (FeLV) are capable of transmitting infectious retrovirus.
  
  
  METHODS
  Fresh cartilage segments and chondrocytes isolated from cats systemically infected with feline leukemia virus were used in this study. Feline embryonic fibroblast cells were cocultured with segments of cartilage, isolated chondrocytes, or fragments of cortical bone from each infected cat. The FeLV p27 antigen was measured in the coculture media by enzyme-linked immunosorbent assay. In addition, FeLV proviral nucleic acids were quantified by real-time quantitative polymerase chain reaction with use of DNA extracted from feline embryonic fibroblast cell cocultures as well as isolated chondrocytes. Immunohistochemistry was used to assess for FeLV p27 antigen in both intact cartilage fragments and isolated chondrocytes.
  
  
  RESULTS
  Feline embryonic fibroblast cells cocultured with cartilage fragments from each of the five FeLV-infected cats all demonstrated high levels of proviral DNA, indicating transmission of infective virus. In addition, media from all cocultures of feline embryonic fibroblast cells and chondral fragments became positive for p27 antigen, indicating active viral replication. In contrast, cocultures of feline embryonic fibroblast cells and isolated chondrocytes from all FeLV-infected cats were negative for proviral DNA and p27 antigen. Likewise, no proviral nucleic acids could be detected in isolated chondrocytes from any infected cats. Cocultures of feline embryonic fibroblast cells with cortical bone fragments were positive for proviral DNA and p27 antigen. Immunohistochemical staining of cartilage fragments from FeLV-infected cats demonstrated the presence of p27 antigen throughout the extracellular matrix, but the p27 antigen was not detected in isolated chondrocytes.
  
  
  CONCLUSIONS
  Articular cartilage fragments can readily transmit infectious retrovirus, but isolated chondrocytes were likely not the source of the infectious virus because they did not harbor proviral DNA or p27 antigen.
authors.affiliation: Laboratory for Comparative Orthopaedic Research and Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA. arnoczky@cvm.msu.edu
authors.forename: Steven P
authors.initials: SP
authors.lastname: Arnoczky
authors.forename: Cheryl
authors.initials: C
authors.lastname: Swenson
authors.forename: Monika
authors.initials: M
authors.lastname: Egerbacher
authors.forename: Keri
authors.initials: K
authors.lastname: Gardner
authors.forename: Oscar
authors.initials: O
authors.lastname: Caballero
authors.forename: Meghan
authors.initials: M
authors.lastname: Burns
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000032:analysis; D001842:Bone and Bones / Q000821:virology; D002358:Cartilage, Articular / Q000821:virology*; D002415:Cats; D002478:Cells, Cultured; D019902:Chondrocytes / Q000821:virology; D018920:Coculture Techniques; D004279:DNA, Viral / Q000032:analysis; D005109:Extracellular Matrix / Q000821:virology; D005347:Fibroblasts / Q000821:virology; D015683:Gene Products, gag / Q000032:analysis; D007150:Immunohistochemistry; D005256:Leukemia Virus, Feline / Q000276:immunology / Q000302:isolation & purification*; D012192:Retroviridae Infections / Q000635:transmission / Q000821:virology; D012191:Retroviridae Proteins / Q000032:analysis; D014412:Tumor Virus Infections / Q000635:transmission / Q000821:virology; D014779:Virus Replication
chemical_list: D000956:Antigens, Viral; D004279:DNA, Viral; D015683:Gene Products, gag; D012191:Retroviridae Proteins; C117471:feline leukemia virus protein p27