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Envelope gene sequences encoding variable regions 3 and 4 are involved in macrophage tropism of feline
Thomas W Vahlenkamp1, Anthony De Ronde2, Nancy N M P Schuurman1
1Virology Unit, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands1.
Abstract:
The envelope is of cardinal importance for the entry of feline immunodeficiency virus (FIV) into its host cells, which consist of cells of the immune system including macrophages. To characterize the envelope glycoprotein determinants involved in macrophage tropism, chimeric infectious molecular clones were constructed containing envelope gene sequences from isolates that had been propagated in peripheral blood mononuclear cells (PBMC). The progeny virus was examined for growth in PBMC and bone marrow-derived macrophages and viruses with different replication kinetics in macrophages were selected. Envelope-chimeric viruses revealed that nucleotide sequences encoding variable regions 3 and 4 of the surface glycoprotein, SU, are involved in macrophage tropism of FIV. To assess the biological importance of this finding, the phenotypes of envelope proteins of viruses derived from bone marrow, brain, lymph node and PBMC of an experimentally FIV-infected, healthy cat were examined. Since selection during propagation had to be avoided, provirus envelope gene sequences were amplified directly and cloned into an infectious molecular clone of FIV strain Petaluma. The viruses obtained were examined for their replication properties. Of 15 clones tested, 13 clones replicated both in PBMC and macrophages, two (brain-derived clones) replicated in PBMC only and none replicated in Crandell feline kidney cells or astrocytes. These results indicate that dual tropism for PBMC and macrophages is a common feature of FIV variants present in vivo.
Insights
The feline immunodeficiency virus (FIV) envelope surface glycoprotein
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- The envelope glycoprotein of feline immunodeficiency virus (FIV) is crucial for host cell entry.
- FIV primarily infects immune cells, including macrophages.
Purpose of the Study:
- To identify envelope glycoprotein determinants responsible for FIV's macrophage tropism.
- To investigate the prevalence of dual tropism for PBMC and macrophages in FIV variants.
Main Methods:
- Construction of chimeric FIV infectious molecular clones using envelope gene sequences from PBMC-propagated isolates.
- Selection of viruses based on replication kinetics in PBMC and bone marrow-derived macrophages.
- Amplification and cloning of provirus envelope gene sequences directly from infected cat tissues (bone marrow, brain, lymph node, PBMC) to avoid selection bias.
Main Results:
- Variable regions 3 and 4 of the FIV surface glycoprotein (SU) were identified as key determinants for macrophage tropism.
- Most FIV variants isolated from various tissues of an infected cat exhibited dual tropism, replicating in both PBMC and macrophages.
- A minority of brain-derived FIV clones showed tropism for PBMC only, not macrophages.
Conclusions:
- Specific regions of the FIV envelope surface glycoprotein (SU) dictate macrophage tropism.
- Dual tropism for PBMC and macrophages is a common characteristic of in vivo FIV variants.