Complement-fixing properties of pepsin-treated rabbit and sheep antibodies

Nonspecific Binding of Complement by Digestion Fragments from Antiviral Gamma Globulin

The nonspecificity of rabbit gamma-globulin (antibody) to western equine encephalitis virus and the non-specificity of normal rabbit gamma-globulin in complement-fixation tests with anti-gens prepared from chick-embryo cells infected with this virus and normal chick-embryo cells resided primarily in Porter's fragment III. Addition of complement to fragment III from the anti-body globulin, followed by inactivation of the added complement, abolished the complement-fixing ability of fragment III with both specific and nonspecific antigens. Similar treatment of the undigested antibody abolished its complement-fixing ability with nonspecific antigen only.

Brucella-Agglutinating Antibodies: Relation of Mercaptoethanol Stability to Complement Fixation

Brucella-agglutinating antibodies from selected bovine blood serums and milk samples did not fix complement, and after treatment with 2-mercaptoethanol they lost agglutinating power. After infection of calves with Brucella abortus, strain 19, agglutinins for Brucella that were inactivated by mercaptoethanol appeared earlier than those stable to mercaptoethanol. Under the conditions of these experiments, the appearance and development of complement-fixing capacity coincided closely with the mercaptoethanol stability of the agglutinins for Brucella.

EPITHELIAL CELL PENETRATION AS AN ESSENTIAL STEP IN THE PATHOGENESIS OF BACILLARY DYSENTERY

LaBrec, Eugene H., Herman Schneider, Thomas J. Magnani, and Samuel B. Formal. Epithelial cell penetration as an essential step in the pathogenesis of bacillary dysentery. J. Bacteriol. 88:1503-1518. 1964.-A parent strain of Shigella flexneri 2a and a colonial mutant derived from it were studied in three animal models. Both strains were equally virulent for mice when living cells suspended in hog gastric mucin were injected by the intraperitoneal route. Feeding the parent strain to starved guinea pigs, followed by the intraperitoneal injection of opium, resulted in the formation of ulcerative lesions in the intestinal tract and in the death of these animals. When the colonial variant was fed to similarly prepared animals, the animals survived and the intestinal tract remained normal. The parent produced diarrheal symptoms and intestinal lesions after its oral administration to rhesus monkeys; the variant caused neither symptoms nor pathology in this species. Studies were carried out to define the characteristics present in the parent strain and absent in the colonial mutant, which would enable the parent to produce ulcerative lesions of the bowel and death in the guinea pig model or intestinal lesions and diarrheal symptoms in the monkey. Neither serological studies nor growth studies conducted both in vitro and in vivo offered a clue to explain this difference. The virulent parent strain was shown to penetrate the bowel epithelium and enter the lamina propria; the avirulent mutant did not do this. Entrance to the lamina propria was by way of the epithelial cell of the mucosa. The avirulent mutant did not possess the capacity to penetrate this cell. This observation was extended to show that the virulent parent possesses the ability to infect and multiply within HeLa cells; furthermore, the organisms are able to penetrate epithelial cells of the guinea pig cornea, causing ulcerative lesions. The avirulent variant possesses neither of these capacities. It is suggested that epithelial cell penetration is a major factor in determining the pathogenicity of dysentery bacilli.

SPECIFIC FRACTIONATION OF HUMAN ANTIDEXTRAN ANTIBODIES. II. ASSAY OF HUMAN ANTIDEXTRAN SERA AND SPECIFICALLY FRACTIONATED PURIFIED ANTIBODIES BY MICROCOMPLEMENT FIXATION AND COMPLEMENT FIXATION INHIBITION TECHNIQUES

Human antidextran of one individual, absorbed specifically on sephadex, was fractionated into two populations of antibody molecules by successive elution with oligosaccharides of the isomaltose series of increasing size. The purified antibody fractions and some whole antidextran sera were found to fix complement with dextrans of molecular weight of 195,000 and above. It could be demonstrated by quantitative microcomplement fixation inhibition assays that the antibody eluted with isomaltotriose had a higher affinity for smaller oligosaccharides relative to isomaltohexaose, indicating a high content of antibody molecules with smaller combining sites, while with the second fraction, eluted with isomaltohexaose, the small haptens were very poor inhibitors and the larger oligosaccharides inhibited readily, presumably due to a higher proportion of molecules with larger combining site size. Assays of similarly prepared fractions, obtained from earlier bleedings of the same individual (1), with inhibition of complement fixation were in good agreement with those obtained by inhibition of precipitation. The two purified antidextran fractions were shown to differ with respect to their complement-fixing capacity. The fraction with molecules with smaller size-combining sites fixed only about half as much complement per unit antibody N as did the fraction containing largely molecules with larger combining sites suggesting that the strength of complement fixation is affected by the strength of the antigen-antibody interaction.

PEPSIN DIGESTION OF RABBIT AND SHEEP ANTIBODIES. THE EFFECT ON COMPLEMENT FIXATION

7S sheep antibody is similar to 7S rabbit antibody, insofar as it too can be digested with pepsin to yield a 5S fragment still capable of precipitating homologous antigen. The 5S fragment from rabbit as well as sheep antibody is capable of fixing guinea pig complement. However, this fixation differs from the fixation by 7S antibody, since preformed antibody-antigen aggregates containing either sheep or rabbit 5S antibody fix only a maximum of 20 to 40 per cent of the total complement. The portion of complement which is fixable by the 5S preformed aggregates seems to be different from the remainder of the complement. Prior treatment of guinea pig serum with 5S washed preformed aggregates removes that portion of complement fixable by 5S antibody, and will leave the complement remaining unable to be fixed by further addition of 5S immune aggregates. Such absorbed complement, however, is as capable as is unabsorbed complement of being fixed by 7S antibody. The 5S sheep and rabbit antibody fixes the portion of complement which it is capable of fixing, as well as or better than the corresponding 7S antibody fixes the total complement. 5S preformed aggregates are broken down by treatment with cysteine, and their complement-fixing ability is lost.

Fixation of Complement to Fragments of Antibody

A specific precipitate of ovalbumin and its rabbit-serum antibody, after fixing human serum complement, was digested with papain. The digest was analyzed immunochemically for complexes of antigen, antibody fragments, and components of complement. The results indicated that complement is not bound to Porter fragment III, but very likely is bound to fragments I and II.