LOCALIZATION OF THE VIRAL-ANTIGEN OF FELINE IMMUNODEFICIENCY VIRUS INTHE LYMPH-NODES OF CATS AT THE EARLY-STAGE OF INFECTION

Immunohistochemical examinations of localization of feline immunodefic iency virus (FIV) Gag protein were performed on lymph nodes of cats ex perimentally inoculated with three different strains of FIV (infectiou s molecular clone of TM1, Petaluma, and KYO-1 strains), using rabbit a nti-FIV Gag serum. The FIV Gag antigens were observed in many follicul ar dendritic cells (FDCs) and sparsely in small lymphocytes of paracor tical area in the lymph nodes of cats inoculated with Petaluma and KYO -1 strains. However, the antigens were present only in small lymphocyt es, and not in FDCs of a cat inoculated with infectious molecular clon e of the TM1 strain. The cell type differences in expression of the vi ral antigen in vivo might reflect on the cell tropisms of the FIV stra ins in vitro. By double immunohistochemical staining with rabbit anti- FIV Gag serum and monoclonal antibodies which recognize feline CD4, fe line CD8 or feline pan-T molecules, the FIV Gag-positive lymphocytes w ere characterized as feline CD4-positive T cells. Since the distributi ons of FIV Gag antigens were mainly in the FDCs, the FDCs may play an important role as a major reservoir and may be a primary target of FIV at early stages of infection.