Human milk fibronectin: identification of fibronectin fragments by transfer of milk proteins from polyarcrylamide gels to nitrocellulose sheets

Abstract

1. INTRODUCTION The term ‘Iibronectin’ describes a family of structural and immunologically related high-Mi, glycoproteins that are present in vertebrates in both the soluble and insoluble form. The soluble form has been observed in various biological fluids in- cluding plasma, cerebrospinal, amniotic and sin- ovial fluids, urine and seminal plasma [l-6]. The insoluble form is present in vertebrate tissue, intra- cellularly, and as an extracellular matrix compo- nent [7- 121. and the cream removed (fat-free milk). Aliquots were then respun at 90 000 X g for 30 min to remove casein (lactoserum). All samples were analyzed within 24 h after drawing. Rabbit monospecific and mouse monoclonal anti-human plasma fibronectin antibodies were prepared as in [2 1,221. Although little is known about the function of fibronectin in vivo, it has been shown to display many interesting features in vitro ([ 13-201 and ref- erences therein). The amount of Iibronectin ,pres- ent on the surface of transformed or neoplastic cells is generally greatly reduced with respect to their normal counterparts. Fibronectin promotes cell aggregation and cell substratum adhesivness, partially restores transformed tibroblasts to a more normal phenotype, promotes locomotion of certain types of cells and facilitates reticuloendothelial sys- tem clearance of particles. Here, we report that human milk contains fibro- nectin and other components of lower M, which are recognized by anti-Iibronectin antibodies. These lower