Characterization of monoclonal antibodies specific for feline serum amyloid (SAA) protein

Monitoring acute phase proteins in retrovirus infected cats undergoing feline interferon-ω therapy

OBJECTIVES

Recombinant feline interferon-ω therapy is an immunomodulator currently used in the treatment of different retroviral diseases including feline immune deficiency virus and feline leukaemia virus. Although its mechanism of action remains unclear, this drug appears to potentiate the innate response. Acute phase proteins are one of the key components of innate immunity and studies describing their use as a monitoring tool for the immune system in animals undergoing interferon-ω therapy are lacking. This study aimed to determine whether interferon-ω therapy influences acute phase protein concentrations namely serum amyloid-A, α-1-glycoprotein and C-reactive protein.

METHODS

A single-arm study was performed using 16 cats, living in an animal shelter, naturally infected with retroviruses and subjected to the interferon-ω therapy licensed protocol. Samples were collected before (D0), during (D10 and D30) and after therapy (D65). Serum amyloid-A and C-reactive protein were measured by specific enzyme-linked immunosorbent assay kits and α-1-glycoprotein by single radial immunodiffusion.

RESULTS

All the acute phase proteins significantly increased in cats undergoing interferon-ω therapy (D0/D65: P<0·05) CLINICAL SIGNIFICANCE: Acute phase proteins appear to be reasonable predictors of innate-immune stimulation and may be useful in the individual monitoring of naturally retroviral infected cats undergoing interferon-ω therapy.

The feline acute phase reaction

The acute phase reaction (APR) is a response to potentially pathogenic stimuli. It begins with the release of interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-α from inflammatory cells. These cytokines induce fever, leucocytosis and release of serum acute phase proteins (APPs). In this review, the characteristics of the feline APR are described. In cats with inflammatory conditions, fever is a common finding, with leucocytosis due to the release of cells from the marginal pool, followed by activation of myelopoiesis. Because excitement frequently causes leucocytosis in cats, a diagnosis of inflammation should therefore be supported by additional findings such as the presence of toxic neutrophils. The major APPs are serum amyloid A and α₁-acid glycoprotein (AGP), which both increase a few hours after the inflammatory stimulus and remain elevated for as long as the inflammation persists. AGP plays an important role in the diagnosis of feline infectious peritonitis (FIP) and may also be useful also in studies of FIP pathogenesis.

Evaluation of feline serum amyloid A (SAA) as an inflammatory marker

The concentration of feline serum amyloid A (fSAA) was determined by a direct enzyme-linked immunosorbent assay (ELISA) by using fSAA specific monoclonal antibodies, to evaluate the fSAA as an inflammatory marker in cats. The mean concentration +/- standard deviation of fSAA was found to be 0.60 +/- 1.06 microg/m l and 33.65 +/- 67.59 microg/ml in serum samples from normal cats (n=45) and cats (n=312) with various diseases and disorders, respectively. A significant difference (p<0.001) was found between the two groups. It was also found that the concentration of fSAA begins to increase rapidly at approximately 3-6 hr after spay, and increases up to significantly high levels in some disorders, like injury, renal failure, infectious diseases, etc.

Identification of feline MAGE-1 gene product by monoclonal antibodies

Melanoma antigens (MAGE) are thought to induce a tumor-specific immune response and to be potential therapeutical targets for cancer immunotherapy. We have earlier identified the cDNA of feline melanoma antigen 1 (fMAGE-1), but its product was not characterized in detail. We have expressed the recombinant fMAGE-1 protein and have generated monoclonal antibodies (mAbs) against it, to identify the native fMAGE-1 protein in feline lymphoma cell lines and tumor tissues. The fMAGE-1 protein was found to be approximately 39 kDa in molecular mass on sodium dodecyl-sulphate-polycrylamide gel electrophoresis (SDS-PAGE), and it was found to be located in the cytoplasm of the cells by immunofluorescence. Immunoblotting analysis detected the fMAGE-1 gene product in the fMAGE-1-mRNA-positive cells, but not in the fMAGE-1-mRNA-negative cells. An interesting finding of the present study was the distribution of the fMAGE-1 protein, which was found to have a spindle-like distribution, with filaments twining around the nucleus, suggesting that the fMAGE-1 protein may be associated with or form some cytoplasmic filaments. This type of finding is so far the first report of its kind, and to the best of our knowledge it has not been reported in either human or mouse MAGE proteins until now. It most probably implies the major diversity of the MAGE family genes.