RESUMO
Familial and secondary deficiency of plasma lecithin-cholesterol acyltransferase (LCAT) produce circulating lipoprotein particles with gross structural and compositional abnormalities; these have adverse effects on a variety of cellular functions. Factors affecting hepatic synthesis and secretion of this plasma enzyme are largely unknown but, potentially, some of them can be investigated with monospecific antibodies. In the present study, enzymically active LCAT was purified 40,000-fold from human plasma and then used to raise polyclonal antibodies in New Zealand White rabbits. Addition of this antiserum (1 mul) to human plasma (25 mul) completely inhibited LCAT activity, although it was less effective against plasma from other species. The antibodies appeared to be monospecific to plasma LCAT. They gave a single precipitin arc by crossed immunoelectrophoresis, while immunodiffusion established that there was no cross-reactivity with several apolipoproteins or with serum albumin. Moreover, the antiserum was successfully used to detect LCAT in normal human plasma by Laurell rocket immunoelectrophoresis. By contrast, Western blotting of plasma proteins using whole LCAT antiserum was largely unsuccessful because of high background staining, although this could be substantially reduced by use of an IgG fraction. However, the whole antiserum readily immunoprecipitated LCAT secreted into the culture medium of HepG2 cells, a human hepatoblastoma cell line, pre-labelled with [35S]methionine, the [(35)S]-labelled LCAT appearing as a narrow 65-kDa protein band by electrophoresis and fluorography. We conclude that polyclonal antibodies may be an important tool to investigate the characteristics and underlying mechanisms of secondary LCAT deficiencies, including those associated with hepatic cirrhosis and schistosomiasis.
