SUPERINFECTION OF CATS WITH FELINE IMMUNODEFICIENCY VIRUS SUBTYPE-A AND SUBTYPE-B

The ability of feline immunodeficiency virus (FIV) isolates from subty pes A and B to superinfect cats and cell cultures was tested, Three sp ecific pathogen-free (SPF) cats were first inoculated with 10 ID50 of subtype B virus (FIVBang) and 30 weeks later inoculated with 100 ID50 of subtype A virus (FIVPet). On the basis of subtype-specific PCR anal ysis, both FIV subtypes were detected in the peripheral blood lymphocy tes (PBLs) of two of three cats from 9 to 30 weeks following the secon d inoculation. Only the first virus was detected in the bone marrow (B M) cells of these two cats until 30 weeks following the second inocula tion, at which time the second virus was finally detected in their BM cells. Both cats developed significant virus-neutralizing (VN) antibod ies to the second virus by 15 weeks following the second inoculation; but only one cat had high VN titers to the first virus, which remained at the same level even after the second inoculation. The two control cats inoculated with only the second virus developed VN titers specifi cally to the second virus and were consistently PCR positive for the v irus in PBLs and BM cells starting 9 weeks postinoculation. Thus a del ay in BM infection with the second virus was observed in the two super infected cats. In contrast, one of three cats had neither VN antibodie s to the second virus nor PCR signal of the second virus in its PBLs, BM, and lymph node throughout the 30 weeks of study and it appeared to be resistant to superinfection. However, this cat bad high constant l evels of both the first virus and VN antibodies to the first virus. In the in vitro superinfection studies, both FIVPet and FIVBang were det ected in the primary PBL cultures after either simultaneous coinfectio n or superinfection (second virus infected 1 week later) and in the FI VPet-producer cell line after superinfection with FIVBang. Thus our in vitro results support our in vivo findings, which suggest that at a c ertain stage of initial FIV infection infected cats can be superinfect ed with another FIV subtype. These findings present the complexity of the FIV immunopathogenicity during multiple FIV exposure and shed some concern as to whether an FIV vaccine developed from a single subtype can completely protect cats against infection with other FIV subtypes. As a small animal AIDS model, our findings should also provide some i nsight into the events that occur during multiple HIV exposure in huma ns and in identifying approaches for HIV vaccine development.