Viral gene expression and provirus load of Orf-A defective FIV in lymphoid tissues and lymphocyte subpopulations of neonatal cats during acute and chronic infections.

Neonatal cats were infected with a wild type (JSY3) or orf-A defective (JSY3DeltaORF-A) feline immunodeficiency virus (FIV) to determine the provirus load and level of viral gene expression at the acute versus chronic stages of infection. FIV DNA in the thymus, lymph node, peripheral blood mononuclear cells (PBMCs) and lymphocyte subpopulations at week 8 post-infection was lower in animals infected with JSY3DeltaORF-A as compared to that of JSY3. At week 16 we observed no significant difference in provirus load between the two groups except for B cells where it was higher in the JSY3 infection. In B cells proviral burden was found to be the same in animals infected with JSY3 for both time points. In the chronic stage, therefore, proviral burden dominates in B cells for JSY3, whereas the level of JSY3DeltaORF-A was lower with comparable values for all lymphocytes at both weeks 8 and 16. Gene expression profiles as measured by real time PCR for gag and rev transcripts revealed decreased levels of JSY3DeltaORF-A mRNAs as compared to that of JSY3. The JSY3 chronic phase infection showed viral gene expression to be higher in B cells relative to CD4+ and CD8+ cells. The presence of viral RNA in CD8 and B cells during the chronic infection implicates active virus replication. Hematological profiles revealed that there was a decline in the number of B cells in JSY3DeltaORF-A-infected cats during the chronic stage of infection while no significant change was observed in animals infected with the wild type virus. Comparative analysis of cell numbers to provirus load and levels of viral transcripts in CD4+ and CD8+, however, did not correlate cell numbers to the levels of viral DNA and gene expression. It remains to be determined whether the relatively high virus burden in B cells as compared to CD4+ and CD8+ cells reflects a role for Orf-A in a shift to B cell virus load during the chronic stage of FIV infection.