CD8⁺Thymic Lymphocytes Express Reduced Levels of CD8β and Increased Interferon γ in Cats Perinatally Infected with the JSY3 Molecular Clone of Feline Immunodeficiency Virus

Abstract

Biological isolates of feline immunodeficiency virus (FIV) cause a relative expansion of activated single-positive CD8(+) (SP CD8(+)) lymphocytes within the thymus of infected cats. In this study, thymic SP CD8(+) lymphocytes were analyzed from cats inoculated as neonates with a pathogenic molecular clone of FIV, JSY3, which was previously derived from the wild-type biological isolate FIV(NCSU-1) (NCSU-1). Four cats were inoculated intraperitoneally with NCSU-1 and compared with 11 cats inoculated with JSY3. Five control cats matched in litter and age were administered an intraperitoneal sham inoculum. Between 12 and 16 weeks postinoculation, interferon-gamma (IFN-gamma) mRNA was quantified by RT-PCR in freshly isolated thymocytes and peripheral blood mononuclear cells (PBMCs). The quantity of IFN-gamma mRNA was increased more than 10-fold in thymocytes and PBMCs of 13 of 13 FIV-inoculated cats as compared with the sham-inoculated controls. IFN-gamma mRNA coenriched with magnetically sorted CD8(+) PBMCs and single-positive (SP) CD8(+) thymocytes. Cells expressing IFN-gamma mRNA were located within the thymic perivascular zone, along the corticomedullary junction, and adjacent to lymphoid follicles. The expansion of thymic SP CD8(+) cells was associated with an increase in CD8alpha(+)/beta(neg) and CD8alpha(+)/beta(lo) phenotypes, the latter population resembling a previously reported memory/effector peripheral blood cell with FIV suppressor activity. From these data we conclude that JSY3 and NCSU-1 induce similar phenotypic changes in thymic and peripheral blood CD8(+) cells. Thus, JSY3 is pathogenic for the thymus in vivo and will be useful for defining determinants of the CD8(+) cell response in this pediatric AIDS model.

Thymic Lesions in Cats Infected with a Pathogenic Molecular Clone or an ORF-A/2 -Deficient Molecular Clone of Feline Immunodeficiency Virus

“…Biweekly hematological profiles were obtained to assess the ability of an ORF-A/2-deficient molecular clone to reduce the peripheral blood CD4/CD8 ratio of infected cats. JSY3 maintains the in vivo biological properties of its parental FIV isolate, NCSU-1, including the inversion of the peripheral blood CD4/CD8 ratio (22,38). PBL profiles were analyzed by flow cytometry in both groups of infected cats.…”

“…Cell-free virus was prepared as described previously (22). Briefly, 4 ϫ 10 5 CrFK cells were plated in cMEM and incubated until growth reached 70 to 80% confluence.…”

“…Although the origin of these cells is unknown, the expanding CD4 Ϫ CD8 ϩ subpopulation may at least be partially responsible for the altered cytokine profiles of FIV-infected thymuses, as has been shown for gamma interferon expression (20,22). Thus, viral replication may mediate some cellular events and contribute to thymic dysfunction.…”

“…Infection of young cats with FIV has been a useful model for pediatric AIDS, particularly when organs normally unaccessible during the disease course such as the thymus are studied (16,22). The thymus has been proposed to be the major site of replication in young hosts during the acute phase of FIV and human immunodeficiency virus (HIV) infection (6,13,36).…”

“…In this study, we describe the in vivo properties of an ORF-A/2-deficient mutant of a highly pathogenic FIV molecular clone, JSY3 (22,38). Our data confirm previous reports of lower in vivo levels of viral replication for ORF-A/2-deficient FIV molecular clones.…”