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Published on: June 19, 2014
Thymic lesions in cats infected with a pathogenic molecular clone or an ORF-A/2-deficient molecular clone of feline
R M Norway1, P C Crawford, C M Johnson
1Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0880, USA.
Abstract:
Previous studies using feline immunodeficiency virus (FIV) molecular clones lacking the putative transactivator gene (ORF-A/2) failed to address the issue of thymus pathogenesis or investigate the levels of viral replication in separate lymphoid compartments (Y. Inoshima, et al., J. Virol. 70:8518-8526, 1996; E. E. Sparger, et al., Virology 205:546-553, 1994). Using a highly pathogenic molecular clone of FIV, JSY3, and an ORF-A/2-deficient mutant, JSY3DeltaORF-A/2, we compared viral replication and the extent of thymic dysfunction as measured by the formation of lymphoid follicles and alteration of the thymocyte subsets. Viral replication was reduced in JSY3DeltaORF-A/2-infected cats as measured by lymphocyte coculture, immunohistochemistry, and quantitative PCR. Cell-associated viral load measured by lymphocyte coculture varied in a tissue-dependent manner with replication highest in lymphocytes isolated from the thymus, lower in those from the peripheral blood, and lowest in those from lymph node. Thymic proviral load and the number of viral p24 Gag-positive cells within the thymus detected by immunohistochemistry were also reduced. In addition, the onset of a reduced peripheral blood CD4/CD8 ratio was delayed in JSY3DeltaORF-A/2-infected cats. The formation and extent of thymic lymphoid follicular hyperplasia were similar in JSY3 and JSY3DeltaORF-A/2-infected cats as measured by anticytokeratin immunohistochemistry and flow cytometry for percent pan T-negative, immunoglobulin G-positive cells within the thymus. In contrast, comparison of thymocyte subpopulations demonstrated a reduced expansion of single-positive CD4(-) CD8(+) thymocytes in JSY3DeltaORF-A/2-infected cats. Level of viral replication, therefore, may not correlate with the formation of thymic lymphoid follicles but may correlate with the expansion of the single-positive CD4(-) CD8(+) thymocyte subpopulation.
Insights
Feline immunodeficiency virus (FIV) replication is reduced without the ORF-A/2 gene, impacting thymus function and delaying CD4/CD8 ratio changes in cats.
Area of Science:
- Virology
- Immunology
- Pathogenesis
Background:
- Previous studies on feline immunodeficiency virus (FIV) molecular clones lacking the ORF-A/2 gene did not fully investigate thymus pathogenesis or viral replication in lymphoid compartments.
- Understanding the role of specific FIV genes in viral replication and immune dysfunction is crucial for developing effective interventions.
Purpose of the Study:
- To compare viral replication and thymic dysfunction in cats infected with a highly pathogenic FIV clone (JSY3) versus an ORF-A/2-deficient mutant (JSY3DeltaORF-A/2).
- To determine the correlation between viral replication levels and thymic pathology, including lymphoid follicle formation and thymocyte subset alterations.
Main Methods:
- Utilized a highly pathogenic FIV molecular clone (JSY3) and its ORF-A/2-deficient mutant (JSY3DeltaORF-A/2) in feline infection models.
- Assessed viral replication through lymphocyte coculture, immunohistochemistry, and quantitative PCR.
- Evaluated thymic dysfunction by measuring lymphoid follicle formation and alterations in thymocyte subsets (CD4/CD8 ratios).
Main Results:
- Viral replication was significantly reduced in cats infected with JSY3DeltaORF-A/2 across various tissues, with the highest load in thymus lymphocytes.
- Thymic proviral load and p24 Gag-positive cells were reduced in JSY3DeltaORF-A/2-infected cats.
- While thymic lymphoid hyperplasia was similar between groups, JSY3DeltaORF-A/2 infection led to reduced expansion of CD4(-)CD8(+) thymocytes.
Conclusions:
- Reduced FIV replication due to the absence of the ORF-A/2 gene correlates with delayed CD4/CD8 ratio reduction and altered thymocyte subpopulations.
- Viral replication levels may not directly influence thymic lymphoid follicle formation but are associated with the expansion of specific thymocyte subsets.
