Isolation and characterization of IgM from bovine colostral whey

Nomenclature of the Proteins of Cows’ Milk—Sixth Revision

This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

Characterization of the gene for the membrane and secretory form of the IgM heavy-chain constant region gene (C mu) of the cow (Bos taurus)

Our present understanding of the evolution of immunoglobulins is derived from a few vertebrate species. In order to obtain additional information on the development of the humoral immune system, we cloned and determined the nucleotide sequence of the bovine cDNA and genomic IgM heavy-chain constant region gene (C mu). The gene contains four constant region domain-encoding exons (CH1 to CH4) and two exons encoding the transmembrane domain (TM1, TM2), expressed in the membrane-bound receptor form of the IgM. The sequence of a cDNA clone encoding the 3' portion of the membrane form of the mu-chain revealed that the TM1 exon is spliced to the CH4 exon, as occurs in other mammals. Comparison of deduced amino acid sequence data from different vertebrates revealed a high similarity to sheep C mu (88%) and a lower degree of similarity to pig (62%), rat (62%), rabbit (58%) human (56%), hamster (55%), mouse (54%), chicken (28%) and horned shark (22%) C mu.

The transport and metabolism of bovine IgM

IgM is present in cows milk, is able to bind secretory component (SC), has a purported role as a secretory immunoglobulin in other species and has been identified with various antibody functions in cows milk. To determine the origin of cows milk IgM, we administered extrinsic 131I-IgM to lactating cows with cannulated bile and parotid ducts and studied the kinetics of its disappearance from serum and its appearance in milk, bile and parotid saliva for 60 hr post-injection. Pentameric IgM appeared to require a long equilibration time and disappeared from serum with a T1/2 of 40 hr. The transport of IgM into bile also appeared biphasic. Results showed that no 131I-IgM was transported intact into parotid saliva and that most radioactivity in milk and bile after 6 hr was in the form of low mol. wt, TCA-precipitable fragments rather than of the size of a pentamer. During the first 24 hr only 0.83% of the administered dose reached the milk in pentameric form, nevertheless, isotope dilution calculations indicated that nearly all milk IgM was derived from serum. During a 12 hr collection period, corresponding to one milking, greater than 200 mg of serum IgM is secreted in milk. During the first 24 hr, only 0.70% of the administered IgM reached the bile as a pentamer. It was calculated that 50% of the pentameric IgM in bile, 3 hr after administration, was serum-derived. Twenty-five per cent of the IgM appearing in bile and ca 10% of the IgM appearing milk, becomes associated with secretory component. A hypothesis to explain the degradation associated with this inefficient transport mechanism is presented.

Characterization of monoclonal antibodies to bovine IgG1

Monoclonal antibodies were developed to bovine IgG1. In addition, production of monoclonal antibodies to bovine light chain is also reported. Monoclonal antibody specificities were initially determined by solid-phase enzyme immunoassay. The monoclonal antibovine IgG1 was shown by a specificity-independent isotyping solid-phase enzyme immunoassay to be mouse IgG1 with kappa light chains. Ascites derived monoclonal antibovine IgG1 antibodies were linked to cyanogen bromide-activated Sepharose and used for affinity isolation of bovine IgG1. The bovine IgG1 eluted from the affinity column was characterized using immuno-electrophoresis, acrylamide gel electrophoresis, isoelectric focusing and solid-phase enzyme immunoassay. Affinity chromatography using monoclonal antibodies provided both a verification of monoclonal antibody specificity and a rapid technique for the isolation of bovine IgG1. This technique may also be employed to remove IgG1 contaminants during purification of bovine IgA.

Congenital abnormalities in newborn calves after inoculation of pregnant cows with Akabane virus

A fresh isolate of Akabane virus was inoculated intravenously into 11 seronegative pregnant cows at 62 to 96 days of gestation. Two of the cows were slaughtered 18 days post-inoculation, and the fetuses were examined; the remaining cows were allowed to give birth. All the inoculated cows developed viremia and neutralizing antibody for the virus, indicating that the cows were actually infected with the virus, although fever or any other clinical abnormalities were not noted. The virus further infected the fetuses. This was proved by virus isolation in one of the two fetuses from the slaughtered cows, and polymyositis was noted in both fetuses. Six of seven calves born alive had anti-Akabane antibody in their precolostral sera, indicating that in utero infection with the virus took place in these calves. Some of the in utero-infected calves demonstrated congenital abnormalities such as cerebral defect, hydranencephaly, and arthrogryposis. These findings provide additional evidence that Akabane virus is the etiological agent of epizootic abortion and congenital arthrogryposis-hydranencephaly syndrome in cattle.

Preparation of antisera to the mu chain of IgM

The protein fraction in the first peak obtained by Sephadex G-200 gel filtration of normal bovine serum was reduced with 2-mercaptoethanol, alkylated with iodoactamide and recycled on a Sephadex G-200 column. The resultant chromatogram indicated the presence of two peaks the second of which was found to be pure monomeric IgM. Immunization of rabbits with the second peak protein resulted in the production of an antiserum with both heavy and light-chain activity. The light-chain activity was simply removed by absorption of the antiserum with glutaraldehyde-polymerized material obtained from the second peak of the initial Sephadex G-200 eluate, yielding an antiserum monospecific for the heavy chain of the IgM molecule.

Nomemclature of the proteins of cow's milk: fourth revision

This report reviews the nomenclature of the milk proteins of cow's milk in light of more recent advances in our knowledge. With the establishment of the primary structures of a number of these proteins, we now have a definite identification of alphas1-, kappa-, beta-, and the gamma-caseins as well as beta-lactoglobulin and alpha-lactalbumin. On the basis of new information on their primary structures and relationship to beta-casein polymorphs, changes in nomenclature have been recommended for proteins of the gamma-casein fraction. Although the primary structure serves as the unambiguous definition of proteins for which it is known, a more practical identification is necessary. We recommend that their behavior in gel electrophoresis under suitable conditions be employed for this purpose for all of the "major" milk proteins of raw skim milk except the immunoglobulins where, because of their heterogeneity and molecular genetics, physical parameters are less useful and their identification must be based upon antigenic determinants and their homology with their human counterparts. More work is needed and, with the accumulation of more information, additional changes in nomenclature can be expected for such proteins as the minor components of alphas- and kappa-caseins, alpha-lactalbumin, and the proteose-peptone fraction as well as further confirmation of the presence of immunoglobulins IgE and additional IgG subclasses. Additional components and genetic variants also can be expected.

Physiochemical characterization of proteolytic cleavage fragments of bovine colostral immunoglobulin G1 (IgG1)

Normal bovine colostral immunoglobulin G1 was subjected to enzymic digestion (pepsin, papain and trypsin) and the resulting fragments separated by a combination of molecularsieve and phosphocellulose chromatography. Fragments F(ab')2 derived from peptic digestion, fragment Fab from papain digestion and fragment Fab(t) from tryptic digestion showed complete antigenic identity with each other. Although fragment F(ab')2 (peptic digestion) had a sedimentation coefficient (S2o,w) of 5.3S, those for fragments Fab' (peptic digestion), Fab (papain digestion) and Fab(t) (tryptic digestion) were found to be 3.9S, 3.7S and 3.7S respectively. The mol.wts. calculated for the various fragments from the sedimentation equilibrium data were: F(ab')2, 104000 +/-200; Fab', 51900+/-340; Fab, 50900+/-230; Fab(t) 50900+/-300. Fragment Fc' (peptic digestion) had an S20,w of 3.2S and a mol. wt. of 42900+/-650; fragment Fc (papain digestion) had an SI0,w of 3.7S and a mol.wt. of 50800+/-300; fragment Fc(t) had an S20,w of 3.7S and a mol.wt. of 50800+/-300; fragment Fc(t) had an S20,w of 3.7S and a mol.wt. of 50800+/-450.