Neutralizing antibodies in cats infected with feline immunodeficiency virus.

Sera from cats experimentally infected with five isolates of feline immunodeficiency virus (FIV) from various geographical regions and from FIV enzyme-linked immunosorbent assay-seropositive field cats from four European countries neutralized the Petaluma strain of FIV (FIV-P), originally isolated in California, at high titers. In addition, FIV-P and a European isolate proved equally susceptible to neutralization by all sera tested. Coupled with observations by Fevereiro et al. (M. Fevereiro, C. Roneker, A. Laufs, L. Tavares, and F. de Noronha, J. Gen. Virol. 72:617-622, 1991), these findings indicate that most if not all FIV strains circulating in Europe and the United States share important neutralization-inducing epitopes.     

Polyclonal B-cell activation in cats infected with feline immunodeficiency virus.

The specificity of the antibody response following natural or experimental infection of domestic cats with feline immunodeficiency virus (FIV) was examined. The antibody response to a range of non-viral antigens, including trinitrophenol (TNP), ovalbumin, beta-galactosidase, deoxyribonucleic acid (DNA) and keyhole limpet haemocyanin (KLH), was measured in 220 cats naturally infected with FIV. Infected cats had higher antibody levels to these antigens, in particular TNP, KLH and beta-galactosidase, than non-infected control cats. Competition binding studies demonstrated that this response was not due to the presence of cross-reacting epitopes on recombinant FIV p17 or p24 antigens, suggesting that the B-cell activation associated with infection was polyclonal rather than entirely virus specific. Studies on cats experimentally infected with FIV revealed a similar pattern, with infected cats developing an antibody response to heterologous non-viral antigens at 6-8 weeks post-infection. There were two discernible peaks of antibody activity, the first occurring 10-20 weeks post-infection and the second peak 40-60 weeks post-infection. The antibody response to KLH, DNA and beta-galactosidase remained elevated throughout the 90-week study period, whereas the antibody levels to the other antigens declined to levels approaching those observed in normal cats.     

Long-term haematological changes in cats experimentally infected with feline immunodeficiency virus (FIV)

Haematological changes of experimental feline immunodeficiency virus (FIV) infection in six inoculated and six control cats were studied over a 98 week period. Acute infection was characterised by moderate to severe leucopenia, neutropenia, and eosinopenia between weeks 5 and 13 post-inoculation (PI). Normal myeloid activity or mild myeloid hyperplasia with a left shift to promyelocytes accompanied neutropenia. Chronic infection was characterised by intermittent neutropenia in three of six cats beginning after week 50 Pl and lymphopenia in two cats starting on week 66 Pl. The severity and duration of neutropenia and lymphopenia varied in individual cats. In contrast to natural FIV infections, anaemia and thrombocytopenia did not develop in either acute or chronic experimental infection. Age-related haematological changes such as increasing packed cell volume and plasma protein concentration as well as decreasing neutrophil and total leucocyte counts were noted as both control and inoculated cats reached maturity. The mechanisms of neutropenia and eosinopenia remain unknown. Viral infection of myeloid cells may be involved in the pathogenesis of cytopenias, and further studies are needed to elucidate the mechanisms. This study also demonstrated that FIV infection in cats may be a useful model in studying haematological abnormalities associated with other immunodeficiency-causing lentiviruses.     

Detection of salivary antibodies in cats infected with feline immunodeficiency virus.

The saliva of cats infected with feline immunodeficiency virus was examined for total immunoglobulin content and antiviral antibodies. Seropositive cats showed an increase in salivary immunoglobulin G levels, which was only partly attributable to the enhanced prevalence of oral inflammatory lesions, compared with the levels in seronegative cats. Immunoglobulin G, but not immunoglobulin M, levels in serum were also increased. Salivary antibodies were determined by indirect immunofluorescence and Western blot (immunoblot) analysis. All but 1 of the 16 seropositive cats examined were positive, while all 16 control cats were negative. The presence of oral lesions was not a prerequisite for antibody detection in saliva. It was concluded that salivary antibody might be usefully exploited for diagnostic and epidemiologic purposes.     

Haematological findings in cats naturally infected with feline immunodeficiency virus

The types and prevalence of haematological abnormalities occurring in FIV infected cats were determined. In addition, the role of FIV infection per se in influencing haematological values was examined by analysing results between infected and non-infected cats which had been allocated to similar clinical disease groups. FIV-positive cats were grouped as asymptomatic carriers (AC), cats with AIDS-related complex (ARC) or AIDS. FIV-negative cats were placed into matched groups using the same criteria and designated as healthy, ARC or AIDS. Healthy FIV-negative cats also formed the reference ranges for peripheral blood and bone marrow. Anaemia was no more frequent in sick (ARC and AIDS) FIV-positive cats than sick (ARC and AIDS) FIV-negative cats. However, it was observed more frequently in FIV-positive cats than FIV-negative cats in the absence of concurrent disease, suggesting a direct effect of FIV infection. Bone marrow was affected by FIV infection; as evidenced by anaemic FIV-positive cats having proportionally less Type I reticulocytes than anaemic FIV-negative cats. In addition, FIV-positive cats demonstrated proportionally fewer mature erythroid cells in their marrow. This implied that FIV may cause a decreased life span or maturation arrest of the erythroid cell line. Lymphopenia and eosinopenia were seen more frequently in AC FIV-positive cats than healthy FIV-negative cats, suggesting the direct involvement of FIV. Thus, although FIV infection affected some haematological findings in AC cats, it appeared that haematological abnormalities in sick FIV-positive cats may be due as much to the disease state as to the virus specifically. Apart from the subjective assessment that bone marrow of FIV-positive cats appeared hypercellular, there were no pathognomonic features for FIV infection.     

Pathological features of lymphoid tissues in cats with natural feline immunodeficiency virus infection.

A range of tissues from a total of 17 cats naturally infected with the feline immunodeficiency virus was examined histologically. In 11 cases, chronic inflammatory lesions were present in various tissues including, most commonly, the intestine, brain and lung. Extensive inflammation in the intestinal wall was present in seven of the cats. No particular bacterial organisms were demonstrated in these inflammatory lesions. A range of changes was present in the lymph nodes, including hyperplasia, atrophy or a mixed pattern. Erythrophagocytosis was a consistent feature. The changes resembled those reported in human acquired immunodeficiency syndrome as a result of infection with human immunodeficiency virus.     

Interaction between human immunodeficiency virus and Toxoplasma gondii replication in dually infected monocytoid cells.

THP-1 monocytoid cells, either not infected or chronically infected with human immunodeficiency virus type 1 (HIV-1), were challenged with Toxoplasma gondii. Parasitic growth, as assessed by trophozoite counting and measurement of supernatant p30 membrane antigen, was similar in HIV-infected and noninfected THP-1 cells. Also, T. gondii did not affect HIV replication. These experiments therefore failed to demonstrate any interaction between HIV-1 and T. gondii replication in concurrently infected monocytoid cells.     

Phylogenetic analysis of feline immunodeficiency virus isolated from cats in Taiwan

Summary.  Feline immunodeficiency virus was isolated from four cats from Taiwan. The isolates were designated TI-1, TI-2, TI-3 and TI-4. Each was isolated from PBMCs following co-cultivation of PBMCs with a feline T-lymphoblastoid cell line (MYA-1 cells). However, the Taiwanese isolates did not grow in a feline kidney cell line (CRFK cells). The nucleotide sequences of the V3-V5 region of the envelope gene of the Taiwanese isolates were determined and compared with those of previously described isolates. Phylogenetic analysis of this region indicates that Taiwanese isolates belong to subtype C. Accepted February 3, 1997; Received November 20, 1996     

Role of TNF and IL-1 in infections with Toxoplasma gondii.

Mice lethally infected with the C56 strain of Toxoplasma gondii and treated with purified recombinant murine tumour necrosis factor (TNF, 1 microgram/day/mouse for 8 days), recombinant human interleukin-1 (IL-1 alpha or IL-1 beta, 100 ng/day/mouse for 5 days) or a single dose of a combination of TNF (1 microgram/mouse) and IL-1 alpha or IL-1 beta (100 ng/mouse) were significantly protected against death (P less than 0.05-0.001, as compared with untreated infected controls). Mice infected with 100,000 tachyzoites of the highly virulent RH strain of T. gondii released serum TNF in relation to the time after infection and were primed to secrete an enhanced level of serum TNF upon stimulation with bacterial lipopolysaccharide (LPS). In vitro studies showed that interferon-gamma (IFN-gamma) increased the antimicrobial activity of murine peritoneal macrophages whereas TNF, IL-1 alpha and IL-1 beta did not. TNF, however, synergized with the anti-toxoplasmic effect provided by IFN-gamma and this activity was blocked by anti-TNF antibodies. IFN-gamma induced the production of TNF and the anti-toxoplasmic effect provided by IFN-gamma seemed to be dependent partly on the production of TNF. We conclude that TNF and IL-1 may play a significant role in modulating the host's immune defence against T. gondii infection.     

Recombinant feline herpesvirus type 1 expressing Toxoplasma gondii ROP2 antigen inducible protective immunity in cats

In order to investigate whether a recombinant viral vaccine composed of a feline herpesvirus type 1 (FHVI) vector and an immunogenic antigen of Toxoplasma gondii can induce a protective immunity in cats, a recombinant FHV1 expressing ROP2 antigen of T. gondii was prepared. We introduced a DNA fragment encoding 1-538 amino acid residues of ROP2 precursor into FHV1 genome under the control of a cytomegalovirus promoter. The recombinant FHV1 (FHV/ROP2) successfully expressed a 59 kDa antigen that was recognized by anti-ROP2 antibodies. Vaccination of cats with FHV/ROP2 induced serum IgG recognizing the native antigen. Moreover the antibodies inhibited the in vitro invasion of tachyzoites. The vaccination also accelerated the IgG response after T. gondii infection and reduced brain parasite load in cats.     

Opportunistic infections and retrovirus-induced immunodeficiency: studies of acute and chronic infections with Toxoplasma gondii in mice infected with LP-BM5 murine leukemia viruses.

Mice infected with LP-BM5 murine leukemia viruses develop a syndrome, termed mouse AIDS (MAIDS), characterized by increasingly severe immunodeficiency and progressive lymphoproliferation. Virus-infected mice were examined for the ability to resist acute infection and to control chronic infection with the protozoan Toxoplasma gondii, a major opportunistic pathogen of individuals infected with human immunodeficiency virus. Mice infected with the retroviruses for 2 or 4 weeks responded normally to challenge with the parasite, but mice inoculated with the protozoan 8 or 12 weeks after viral infection died with acute disease due to T. gondii. Increased sensitivity to acute infection was associated with a reduced ability to produce gamma interferon (IFN-gamma) and with established changes in CD4+ T-cell function. Mice latently infected with T. gondii and then inoculated with the retrovirus mixture were found to reactivate the parasite infection, with 30 to 40% of dually infected animals dying between 5 and 16 weeks after viral infection. Reactivation was associated with reduced proliferation and impaired production of IFN-gamma in response to stimulation with soluble T. gondii antigens or to concanavalin A. Continuing resistance to lethal reactivation in the remaining mice was shown to require CD8+ T cells and expression of IFN-gamma. In addition, it was found that chronic infection with T. gondii altered the course of MAIDS by inhibiting the progression of splenomegaly and immunodeficiency and reducing the expression of both the helper and etiologic defective viruses. These results support previous studies which indicate that infection with T. gondii is controlled by synergistic interactions between CD4+ and CD8+ T cells, the functions of which are progressively impaired during the course of MAIDS.     

Detection of apoptosis induced in peripheral blood lymphocytes from cats infected with feline immunodeficiency virus

Summary Peripheral blood lymphocytes (PBL) from cats infected with feline immunodeficiency virus (FIV) were examined for the occurrence of apoptosis after short-term culture. In the PBL from FIV-infected cats, changes in flow-cytometry scattergram, morphological characteristics of apoptosis and nucleosomal DNA fragmentation were observed. Percentages of apoptotic cells by flowcytometry analysis in PBL from FIV-infected cats (22.4%±9.4%) were significantly higher than those in PBL from uninfected control cats (9.2%±3.5%). The lymphocytes which underwent apoptosis included CD5⁺, CD4⁺ and sIgM⁺ cells, indicating that induction of apoptosis was not restricted to a special subset of lymphocytes. These findings provide evidence of the apoptotic state of PBL in cats with FIV infection.     

Severe Toxoplasma gondii I/III recombinant-genotype encephalitis in a human immunodeficiency virus patient

The reactivation of an uncommon type I/III recombinant-genotype Toxoplasma gondii strain resulted in unusually severe encephalitis and chorioretinitis associated with a cerebral salt wasting syndrome in an African human immunodeficiency virus patient. This observation suggests an influence of the parasite genotype on disease expression in immunocompromised patients.     

Problems with serological diagnosis of Toxoplasma gondii infections in heart transplant recipients.

Of the first 128 patients to receive either heart or heart and lung transplants at Papworth Hospital, four developed Toxoplasma gondii infections acquired from the donor heart and two died. Six patients had passively acquired T gondii antibody as a result of blood transfusions around the time of transplantation. Eight patients developed antibodies against T gondii, which were detectable by changes in the latex agglutination test titres but not by those of the dye test. These false positive latex agglutination reactions occurred simultaneously with cytomegalovirus infection and were associated with the IgM serum fraction in the patients' sera. These reactions were not associated with cytomegalovirus specific IgM, Paul-Bunnell antibody, nor detectable rheumatoid factor. These findings emphasise the need for T gondii dye test confirmation of latex agglutination test titre rises in heart transplant recipients.     

Identification of Toxoplasma gondii infections by BI gene amplification.

The diagnosis of toxoplasmosis in congenitally infected children or in immunocompromised patients can be difficult; serology is not reliable, and the diagnosis must be based on the combination of symptomatology and the direct demonstration of the parasite in clinical specimens by microscopy, antigen detection, or inoculation of samples into mice or tissue cultures. These techniques are either insensitive or time-consuming. To determine the value of the polymerase chain reaction (PCR) for the diagnosis of Toxoplasma gondii infections, we compared this technique with conventional detection techniques, such as microscopy, tissue culturing, and mouse inoculation. We were able to detect T. gondii by PCR in clinical specimens and tissue samples that were obtained postmortem from a bone marrow recipient with cerebral toxoplasmosis and from three congenitally infected children. The presence of T. gondii was demonstrated in brain tissue, cerebrospinal fluid, the heart, and skeletal muscle tested fresh or after fixation in Formalin. In only one sample was T. gondii isolated by mouse inoculation but not detected by PCR. Because it is a sensitive, relatively rapid, and specific method and because it can be applied to a variety of different clinical samples, PCR can be considered a valuable additional tool for the identification of T. gondii infections.