Franco Tozzini

Prevalence of feline immunodeficiency virus and other retroviral infections in sick cats in Italy

Two hundred and seventy-seven sick pet cats living in Italy were tested for antibodies to feline immunodeficiency virus (FIV) and for feline leukemia virus (FeLV) antigen. Overall, 24% of the cats resulted positive for anti-FIV antibody and 18% for FeLV antigen. FIV was isolated from the peripheral mononuclear blood cells of ten out of 15 seropositive cats examined and from one out of eight saliva samples. No FIV isolations were obtained from six serum samples cultured. Feline syncytium forming virus (FeSFV) could be isolated from blood and/or saliva in ten out of 11 FIV seropositive cats examined, in six out of nine FeLV antigen positive cats, in two cats found positive for both infection markers, and in three out of 11 cats negative for both markers. Thus, the probability of isolating FeSFV was enhanced by infection with other exogenous retroviruses.

Simple in vitro methods for titrating Feline Immunodeficiency Virus (FIV) and FIV neutralizing antibodies

The feline immunodeficiency virus (FIV) readily produced syncytia in Crandell feline kidney (CrFK) cells adapted to a medium containing 0.5% fetal calf serum, a variety of growth factors and other supplements. This finding has been exploited to develop simple and sensitive virus titration and neutralization assays. High titre neutralizing antibodies were detected in cats infected naturally and experimentally with FIV, but not in uninfected animals.

FIV VACCINE STUDIES. I: IMMUNE RESPONSE TO RECOMBINANT FIV ENV GENE PRODUCTS AND OUTCOME AFTER CHALLENGE INFECTION

We have vaccinated five groups of cats (n = 25) four times with five preparations of recombinant feline immunodeficiency virus (FIV) env gene products; one group (n = 7) served as control. The vaccine formulations were as follows: (1) envelope glycoprotein of FIV Zurich 2 (FIV Z2) expressed in a Baculovirus system and isolated by gel electroelution (denatured form); (2) insect cells expressing FIV Z2 glycoprotein; (3) envelope glycoprotein of a Boston strain (FIV Bangston) expressed in insect cells and isolated by gel electroelution (denatured form); (4) glycosylated Bangston envelope protein made in insect cells and isolated in a native form; (5) non-glycosylated Bangston envelope protein made in Escherichia coli. All cats were challenged with 20 50% cat infective doses (CID50) of FIV Z2 previously titrated in cats. All vaccinated cats developed high enzyme-linked immunosorbent assay (ELISA) antibodies to the homologous antigen; crossreactivity to heterologous antigens was seen at a lower level. Virus neutralizing antibodies (tested with Petaluma virus) reached titers up to 32. After challenge, all cats seroconverted (as judged by anti gag antibodies in Western blot) and became infected (as judged by virus isolation and/or polymerase chain reaction) between 4 and 11 weeks with the exception of one cat. It is concluded that it is relatively easy to induce high ELISA antibody titers using recombinant env gene products, ELISA antibody titers do not correlate with virus neutralization or with protection.

Experimental infection of European wild swine (Sus scrofa L.) with pseudorabies virus.

Experimental infection with pseudorabies virus was carried out by oral exposure of four young wild swine held in contact with two unexposed controls. No disease was observed but virological procedures indicated that the virus was shed in saliva and, in one case, in the nasal discharge, with subsequent infection of the control animals. After slaughter the virus was reisolated from the tonsils but not from lungs and brain. Virus reisolation from the tonsils was obtained in two animals after the throat swabs became negative. Virus neutralizing antibodies were detected.

Epitope mapping of the V3 domain of feline immunodeficiency virus envelope glycoprotein by monoclonal antibodies

A panel of six IgG monoclonal antibodies (MAbs) was produced by immunizing mice with a 22 amino acid synthetic peptide, designated V3.3, of the third variable region of feline immunodeficiency virus (FIV) envelope glycoprotein. This peptide is known to induce neutralizing antibodies in cats. In ELISA all MAbs reacted with purified SDS-disrupted FIV and in flow cytometry all MAbs stained permeated, persistently infected FL4 cells but not unfixed FL4 cells; this indicated that the MAbs recognize essentially cryptic epitopes of the gp100 V3 loop. By direct ELISA using partially overlapping synthetic peptides and by competition binding studies, the anti-V3.3 MAbs were shown to detect at least four distinct epitopes, two located in the amino-terminal half and two in the carboxy-terminal half of the sequence. When tested for neutralizing activity by the syncytium inhibition assay in Crandell feline kidney cells, all anti-V3.3 MAbs neutralized FIV at high dilution. However, at low dilution two MAbs exhibited much less neutralizing activity. These results indicate that the V3 region of FIV contains multiple epitopes involved in neutralization.

Small Animal Model of AIDS and the Feline Immunodeficiency Virus

Many aspects of the virology, epidemiology and prevention of AIDS are fairly well known, but the mechanisms whereby HIV produces the characteristic severe immune deficiency remain essentially obscure. Even more importantly, the armamentarium for controlling HIV infection is still extremely limited. For these reasons it is generally believed that AIDS research might profit greatly from the study of animal models.