INSULIN ANTIBODY VARIATIONS IN RABBITS AND GUINEA PIGS AND MULTIPLE ANTIGENIC DETERMINANTS ON INSULIN

GENETIC DIFFERENCES IN ANTIBODY PRODUCTION TO DETERMINANT GROUPS ON INSULIN

Highly inbred strain 2 guinea pigs can produce antibodies to portions of the insulin molecule to which strain 13 guinea pigs cannot produce antibodies. Such differences were not observable within either strain. Consequently it is probable that genetic factors regulate antibody production with respect to the determinant groups toward which antibodies are directed.

INTERFERENCE WITH IMMUNE HEMOLYSIS BY GLYCOPROTEIN ANTIGENS

1. The titer of an individual insulin antiserum measured by hemagglutination agrees favorably with the titer of the same antiserum as measured by immune hemolysis. 2. In contrast, a marked decrease is noted in the immune hemolysis titers relative to hemagglutination titers of antisera prepared against three different sialic acid-containing proteins (human chorionic gonadotropin, rabbit transferrin, and human transferrin). 3. The lower immune hemolytic titers of glycoprotein antisera are apparently not due to a lack of complement-fixing gamma(2)-antibodies. 4. The glycoprotein antigens in solution do not interfere with hemolysis in the insulin immune system. 5. By contrast, marked inhibition of insulin immune hemolysis occurs when cells are sensitized with both glycoprotein and insulin. 6. Cells treated with neuraminidase (to remove cell surface sialic acid) lyse in the presence of C'(a) alone. 7. If neuraminidase-treated cells are sensitized with sialic acid-containing protein, the lysis of these cells by complement is inhibited. 8. It is, therefore, postulated that during some initial phase of immune hemolysis, a sialic acid-containing substrate is cleaved from the cell surface, rendering the cell susceptible to lysis. If this removal is interfered with, i.e., by sensitization of the cell with competitive sialic acid-containing antigen, then the lytic portion of immune hemolysis cannot proceed.

Spontaneous diabetes mellitus associated with persistent bovine viral diarrhea (BVD) virus infection in young cattle

Histologic and immunohistochemical studies were carried out on four young cattle with diabetes mellitus associated with persistent bovine viral diarrhea (BVD) virus infection. Clinical findings included persistent hyperglycemia, decreased glucose tolerance, glycosuria, polydipsia, and severe emaciation. Macroscopically, multiple erosions and ulcers in the mucosa of upper and lower alimentary tracts and swollen lymph nodes were commonly observed. Erosions and ulcers in the mucosa of tongue, esophagus, and forestomach were represented histologically by necrosis of squamous epithelium with neutrophilic infiltration. In the small and large intestines, villous atrophy and suppurative cryptitis were often observed, along with diffuse infiltration of lymphocytes and macrophages and fibroplasia in the lamina propria. In the pancreas of all cattle, there was a reduction in the number of islet cells, and most of the residual islet cells had hydropic degeneration and a decreased number of secretory granules. Immunohistochemical examination confirmed that these cells were severely degranulated beta-cells. In addition, many islets containing necrotic islet cells were observed. These islet cells had increased eosinophilia and shrinkage of cytoplasm, as well as pyknotic nuclei. Inflammation of the islets with mild infiltration of lymphocytes was observed in all pancreatic lobes. In addition, bovine IgG-immunoreactive cells were identified immunohistochemically in the affected pancreatic islets. The BVD virus antigen was not identified in the cytoplasm of the islet cells by immunohistochemical study, although it was identified in the epithelial cells of the small intestine. The histologic and immunohistochemical studies demonstrated that the pancreatic lesions in these animals were similar to those caused by acute insulin-dependent diabetes mellitus (IDDM) in human beings.(ABSTRACT TRUNCATED AT 250 WORDS)

Disappearance rate of insulin antibodies after discontinuing insulin treatment in 42 type 2 (non-insulin-dependent) diabetic patients

The disappearance rate of insulin antibodies was studied after cessation of insulin treatment which had been given for 3 months to 6 years in 42 Type 2 (non-insulin-dependent) diabetic patients. Insulin antibodies were measured before and 15 days after interruption of insulin treatment, and every 30 days until the disappearance of insulin antibodies. The mean +/- SD value of insulin binding in the entire group before the interruption of insulin treatment was 32 +/- 14%. There was no relationship between the antibody level at that time and the duration of insulin treatment. However, the insulin antibody level was significantly higher in 17 diabetic patients on an insulin dose of greater than 20 U/day (p less than 0.02) than in 25 on an insulin dose of less than 20 U/day (39 +/- 13% versus 28 +/- 12%). A positive correlation was found between initial insulin binding and the time required for it to fall below 10% (r = 0.74). Antibodies were absent 60 days after discontinuing insulin treatment in eight of ten subjects presenting with initial binding of less than 20%. In contrast, in only two of 12 patients with an initial binding of greater than 40% were insulin antibodies detectable 150 days after discontinuation of insulin therapy. Disappearance of insulin antibodies sometimes took up to 1 year and occasionally even more than 2 years.

Subpopulations of antibodies directed against evolutionarily conserved regions of the insulin molecule in insulin-treated patients

In the present study, we attempted to define possible subpopulations of antibodies which theoretically could be directed against evolutionarily conserved regions of the insulin molecule in sera from insulin-treated diabetic patients using a variety of labelled and unlabelled insulins which differ widely in structure but are very similar in functional properties. Ten high titre human insulin antisera from patients treated with mixed beef-pork insulin were examined. All sera were found to bind 125I-pork insulin better than labelled chicken insulin which bound better than labelled fish insulin. Detailed studies were conducted with four of the antisera using the pork and fish tracers. With two of the antisera, a subpopulation of antibody could be detected with 125I-fish insulin which had similar affinity for both fish and pork insulin, but reacted much less well with guinea pig insulin and the desoctapeptide derivative of porcine insulin. Based on the known properties of these four insulins, the data provide suggestive evidence consistent with the hypothesis that there are subpopulations of antibodies recognizing regions on the insulin molecule that are well conserved, possibly the region involved in the formation of insulin dimers or receptor binding.

Immune response gene control of determinant selection. I. Intramolecular mapping of the immunogenic sites on insulin recognized by guinea pig T and B cells

T-cell DNA synthesis and T-helper cell function in response to isolated insulin chains and naturally occurring insulin variants was assessed in insulin immune guinea pigs. Two distinct antigenic determinants, recognized by T cells, were defined. One localized in the B chain and the other one constituted by amino acids A8, A9, and A10 of the insulin A-chain loop. Recognition of the B-chain determinant is under the control of Ir genes linked to the strain 13 major histocompatibility complex. This was shown by studying the response to isolated insulin B chain in F1(2 x 13) guinea pigs, as well as serologically defined backcrosses and outbred animals. Insulin recognition through the A-chain loop determinant is specific for strain 2 guinea pigs. These animals recognize this region of the molecule even when displaying different amino acid sequences. The strain differences observed in those antigenic sites eliciting T-cell recognition was not found at an antibody level. No differences could be detected in the ability of the different insulin variants to inhibit the binding of 125I-labeled pork insulin to strain 2 guinea pig anti-pork insulin or to strain 13 guinea pig anti-pork insulin.

Methylation of the flagellin of Salmonella typhimurium

The methylation of endogenous proteins by Salmonella typhimurium SL 870 was investigated in cell-free extracts by using S-adenosylmethionine as methyl donor. Several lines of evidence are presented which suggest that one of the methylated products is the protein flagellin. Mutant strains of SL 870 (nml(-)fla(+) and nml(+)fla(-)) were also found to synthesize epsilon-N-methyl-lysine. It is proposed that S. typhimurium possesses at least two genes specifying different methylating enzymes. One gene product is a flagellin-specific methylating enzyme, whereas the other gene(s) codes for enzymes that methylate one or more other cell proteins.

Immunological and biological properties of iodoinsulin labeled with one or less atoms of iodine per molecule

Experiments were designed to compare the distribution of free and antibody-bound unlabeled insulin to the distribution of free and antibody-bound insulin-(125)I. The insulin antibody was incorporated in a specific immune precipitate similar to the one used by Hales and Randle for the radioimmune assay of insulin. Insulin which was not bound by the specific immune precipitate was measured by the immune hemolysis inhibition assay. This report contains evidence that the addition of the unlabeled insulin in the radioimmune assay results in relatively more insulin-(125)I which remains free and less bound by antibodies than is the case with the unlabeled insulin. Methods are described for the separation of an electrophoretically homogeneous iodoinsulin from samples of crude iodoinsulin with average incorporations of less than 0.2 atoms iodine per molecule. These purified iodoinsulin fractions have a markedly attenuated biological activity. Evidence is presented which supports the postulate that only a portion of the antibodies in guinea pig insulin antiserum are capable of effectively binding with purified iodoinsulin.

Genetic control of combining sites of insulin antibodies produced by guinea pigs

1. Genetic factors control the configuration of combining sites of guinea pig insulin antibodies. 2. It is possible that the configuration of the combining sites of guinea pig insulin antibodies is controlled by more than one gene and not by multiple alleles at a given gene locus.

Antibodies against the Component Polypeptide Chains of Bovine Insulin

Antibodies were produced in guinea pigs against A and B chains of bovine insulin; the chains were prepared by cleavage of all the disulfide bonds with sulfite. Antibodies against A chain reacted with A chain, but not with B chain or native insulin. Antibodies against B chain reacted strongly with both B chain and insulin, but not with A chain. Antibodies against insulin reacted strongly with insulin, weakly with B chain, and not at all with A chain. The results indicate that the insulin-reactive antibodies in antiserums to B chain and to insulin differ and are directed to differing individual antigenic regions of the insulin molecule.