EARLY STAGES OF FELINE IMMUNODEFICIENCY VIRUS-INFECTION IN LYMPH-NODES AND SPLEEN

Analysis of the early stages of infection within the lymphoid organs i s crucial for the understanding of the physiopathology of HIV infectio n. Such analysis can only be performed using animal models. Cats were infected with two strains of FIV and killed at regular intervals for a classic pathologic study along with a quantification of the viral loa d by in situ hybridization in the spleen and the lymph nodes. The path ological study showed a persistent follicular reaction, which peaked 1 5 days postinoculation (p.i.). The in situ hybridization study showed two types of labeling. The first was spot labeling corresponding to ce lls actively replicating the virus. The second consisted of a more dif fuse labeling linked to the follicular dendritic cells (FDCs) demonstr ating by colocalization of virus detected by in situ hybridization ass ociated with the FDCs, specifically labeled by immunohistochemistry. T he number of productive cells is few and identical for the two viruses tested, Despite a slight peak at 15 days p.i., the number of infected cells persists while slightly decreasing over time. The FDC virus loa d appears jointly with the appearance of antibody and remains permanen t until the end of the study at 3 years p.i. These results show that i n the FIV model, there is a chronic permanent infection in the lymphoi d organs. Furthermore, as compared with the SIV-macaque model, there i s a correlation between the low number of infected cells detected in t hese organs in the early phase and the extended length of the asymptom atic period, which contrasts with the high level of the FDC virus load lasting during the same period.