A micro-enzyme-linked immunosorbent assay (ELISA) test for detection of feline leukemia virus in cats

Exposure to disease agents in the endangered Iberian lynx (Lynx pardinus)

The Iberian lynx (Lynx pardinus) is the most endangered felid species in the world. Lynx populations have decreased dramatically in size and distribution in the last four decades, thus becoming increasingly vulnerable to catastrophic events such as epizooties. From 1989 to 2000, serum samples were obtained from 48 free-ranging lynx captured in the Doñana National Park (DNP, n = 31) and mountains of Sierra Morena (SM, n = 17) in southern Spain. Samples were tested for antibodies against Toxoplasma gondii, feline herpesvirus 1 (FHV-1), feline calicivirus (FCV), feline/canine parvovirus (FPV/CPV), feline coronavirus, feline immunodeficiency virus (FIV), feline leukaemia virus and canine distemper virus (CDV) and for FeLV p27 antigen, to document baseline exposure levels. Antibodies against T. gondii were detected in 44% of lynx, with a significantly greater prevalence in DNP (61%) than in SM (12%). In DNP, prevalence was significantly higher in adult (81%) than in juvenile and sub-adult (41%) lynx, but no such difference was observed in SM. Low prevalences (≤11%) of minimally positive titres were found for FHV-1, FCV and FPV/CPV. This, combined with the lack of evidence for exposure to CDV, FIV and FeLV, suggests that these lynx populations are naïve and might be vulnerable to a disease outbreak in the future. Because of the reduced size of lynx populations, the documented low level of genetic variation (particularly in the DNP population) coupled with the recently documented state of immune depletion in a majority of necropsied lynx, it is important to better understand the threat and potential impact that disease agents might pose for the conservation of this endangered species. Future surveillance programs must include possible disease reservoir hosts such as domestic cats and dogs and other wild carnivores.

Feline leukemia/sarcoma viruses and immunodeficiency

This chapter discusses the structure feline leukemia virus (FeLV) and pathogenesis of lymphomas and leukemias BY FeLV. FeLV is quite similar to the better-studied murine leukemia viruses in structure and genetic map. The virus particles bud from cytoplasmic membranes into either extracellular spaces or into vacuoles. FeLV has long been considered a typical noncytopathogenic, longlatency leukemia virus based on its behavior in fibroblasts in vitro . Recent evidence suggests that its in vivo behavior in critical target hemolymphatic tissues is as likely to be cytopathic as transforming. The type of FeLV-related disease that occurs and the disease-free interval probably are influenced by viral envelope proteins and glycoproteins and the consequences of proviral integration. FeLV subgroup specificity apparently determines when and what type of disease will occur. The ecotropic FeLV-A is the most frequent subgroup found in pet cats and is transmitted contagiously. Immunosuppression is the most frequent and the most devastating manifestation of FeLV viremia in clinical and experimental studies. It seems that multiple cell types and multiple processes are involved in the development of feline retrovirus-induced immunosuppression. Although no solid evidence is available for the malfunctioning of cat T helper cells because of the paucity of T-cell specific markers, the circumstantial evidence provided thus far indicates an impaired T helper function in FeLV-infected cats similar to that observed in humans infected with HIV. Studies on the pathogenesis of FeLV-induced immunosuppression might provide a valuable mode for a better understanding and means of control of human AIDS.

Characterization of a newly established feline lymphoma-derived cell line (BKD) lacking T and B cell surface markers

A new feline lymphoma-derived cell line, designated BKD, was isolated from an anterior mediastinal tumor. Cells of this line were characterized as lymphoid based on morphology, the lack of intracellular esterase and peroxidase activity, and absence of phagocytic function. In contrast with other established feline lymphoma-derived cell lines, cells of the BKD line lack characteristics of both feline T-cells and B-cells in that they neither form rosettes with guinea pig erythrocytes nor have demonstrable surface or cytoplasmic immunoglobulin. Approximately one third of BKD cells form EAC rosettes, a significant number of rosette forming cells (p = 0.0001) when compared to background sheep E-rosetting activity. In addition, a consistently titratable level of interleukin-2-like activity was produced when BKD cells were coincubated with concanavalin A and phorbol-12-myristate-13-acetate. Chromosome analysis showed that a majority of BKD cells are diploid. This new cell line has been continuously replicating in culture for over one year and produces feline leukemia virus as demonstrated by several analyses.

Changing manifestations of a chronic feline haematopoietic proliferative disease during immunotherapy with staphylococcal protein A

A cat with feline leukaemia virus-associated malignant disease was treated by ex vivo immunoadsorption using staphylococcal protein A coated filters. During the 12-week course of treatment, the morphological manifestations of the haematopoietic disease showed a progressive transition from erythroid to myeloerythroid to myeloid predominance, and the disease was preceded by and associated initially and terminally with a blast transformation of lymphoblastic morphology. Necropsy revealed massive meningo-cerebral, as well as hepatic, renal, myeloid, lymphoid, peritoneal and pelvic infiltrations largely consisting of lymphoblastic cells. Evidence of myeloid and erythroid differentiation was present in all the infiltrates. The several possible bases for this shift of morphological expression are considered.

Hypercalcemia in cats with feline-leukemia-virus-associated leukemia-lymphoma

Three cases of hypercalcemia were recognized among 11 cats presenting with leukemia-lymphoma for ex vivo immunoadsorption therapy using Staphylococcal Protein-A-coated filters. In addition, the initial mean serum calcium concentration of cats with leukemia-lymphoma was significantly higher (P less than 0.005) than that of healthy control cats or feline-leukemia-virus-infected cats without malignancy. During immunotherapy of the hypercalcemic cats, objective reduction in the extent of the malignancies was associated with a small reduction in the serum calcium concentrations. This response to treatment, the lack of skeletal metastasis, and the absence of renal and parathyroid pathologic findings imply that humorally mediated mechanisms may have been responsible for the production of the hypercalcemia.

Polyclonal induction of immunoglobulin synthesis by feline leukocytes as identified in a reverse hemolytic plaque assay

Optimal conditions of culture and assay for identification of feline immunoglobulin-secreting mononuclear cells were determined for the staphylococcal protein A-reverse hemolytic plaque assay (SpA-RHPA). Hemolytic plaques were most distinct and numerous when peripheral blood mononuclear cells were stimulated with 6.9 micrograms/ml pokeweed mitogen for 7 days. Immunoglobulin-secreting cells were identified morphologically within a zone of hemolysis utilizing a 1:5 dilution of rabbit anti-cat IgG and a 1:30 dilution of guinea pig complement as developing reagents. The SpA-RHPA system should contribute to an understanding of normal feline T- and B-lymphocyte interactions and will likely aid in the identification and understanding of immune cell dysfunctions associated with chronic feline leukemia virus infection.