Comparative study of the plasma globulin level, CD21− B-cell counts and FOXP3 mRNA expression level in CD4+ T-cells for different clinical stages of feline immunodeficiency virus infected cats

Feline immunodeficiency virus (FIV) infection leads to hypergammaglobulinemia through mechanisms that remain poorly understood. We investigated changes in plasma globulin level, B cells, and T cells with progression of the clinical stage of FIV-infected cats. We classified FIV-infected cats into the stage of Asymptomatic carrier (AC) and AIDS-related complex (ARC) based on the clinical symptoms, and measured the plasma globulin level, the CD4+ T-cell counts, and analyzed surface markers of B cells. We investigated the relationship between the plasma globulin level and regulatory T cells (Tregs) using the Forkhead box P3 (FOXP3) mRNA expression level. In FIV-infected cats, the plasma globulin level and the surface immunoglobulin (sIg)+ CD21− B-cell counts were increased, whereas the CD4+ T-cell counts were decreased compared with specific-pathogen free (SPF) cats. The mRNA expression of Blimp-1 (master gene of plasma cells) was increased in peripheral blood, and the FOXP3 mRNA expression level was decreased in CD4+ T-cells. These immunological changes were marked in the ARC stage. These data indicate that the decrease of Tregs and the increase of plasma cells lead to hypergammaglobulinemia.