Loss of naïve (CD45RA+) CD4+ lymphocytes during pediatric infection with feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) infection of cats is an animal model for the pathogenesis of CD4+ lymphopenia and thymus dysfunction in HIV-infected humans. Recently, a monoclonal antibody (755) was reported to recognize the feline homologue to CD45RA, allowing the enumeration of naïve T cells in cats. We tested the hypothesis that pediatric FIV infection would be associated with a selective loss of naïve CD4+ lymphocytes by inoculating newborn cats with a pathogenic clone of FIV (JSY3) or a related clone with an inactive ORF-A gene (JSY3-DeltaORFA), and compared the data to age-matched uninfected control cats. Both FIV inocula were associated with a reduction in the CD4-CD8 ratio (p=0.01), which was attributable to a disproportionate loss of naïve CD4+ cells (p=0.01) vs. naïve CD8+ cells. Therefore, the reduced CD4:CD8 ratio in FIV-infected juvenile cats is associated with a selective depletion of naïve CD4+ cells from the blood.