The influence of Igh-1 genes on the class and subclass distribution of oxazolone-specific antibodies

Previous studies have demonstrated that the level of the oxazolone-specific antibody response induced by contact sensitization is under the control of H-2 and Igh-1-linked genes. The aim of the present study was to clarify the role of H-2 and Igh-1 genes in the regulation of antibody affinity and isotype composition of oxazolone-specific antibodies. Analysis of the antibody response to oxazolone has revealed different ratios of IgG2a and IgG2b antibodies in mice carrying the Igh-1b allele and in strains carrying alleles a, c, and e. The characteristic ratio of IgG2a and IgG2b isotypes persisted during the whole period of the primary and secondary antibody response of CBA and CBA-Igb Igh-C congenic mice. The Igh-1-linked genes influenced the isotype distribution and not the affinity of oxazolone-specific antibodies induced by contact sensitization.

Fc-dependent effector functions of idiotype-anti-idiotype immune complexes

Some effector functions of antigen-antibody and antibody-antibody (idiotype-anti-idiotype) complexes were analyzed. As a model system a monoclonal IgM antibody specific for the hapten NP (antibody B1-8) was reacted either with hapten and hapten-carrier conjugates or with monoclonal anti-idiotope antibodies with specificity for B1-8 idiotopes. The precipitating, C1q-binding, complement-activating and Fc receptor binding properties of these complexes were compared. Binding of both hapten-carrier conjugates and anti-idiotope antibodies to B1-8 results in formation of complexes which depending on the B1-8:ligand ratio precipitate, activate complement, bind C1q and exhibit increased avidity for Fc mu and Fc gamma receptors of mouse spleen cells. In both types of complexes cross-linking of IgM molecules is essential for triggering these Fc-dependent functions, and a functional heterogeneity if idiotype-anti-idiotope complexes based on different idiotype-anti-idiotope ratios could also be observed. The functional similarity of B1-8-hapten-carrier and B1-8-anti-idiotope complexes suggests that regulatory functions so far assigned to antigen-antibody complexes could be carried out also by idiotype-anti-idiotope complexes.

Interaction of C3 and C3b with immunoglobulin G

Human C3b as well as native C3 were found to bind to solid phase human and rabbit IgG. Haemolytically active C3 had significantly higher binding capacity to IgG than the C3b fragment. Inhibition experiments proved that C3 and C3b have common binding sites on the Fab and Fc part of the IgG molecule but the character of these binding sites was different. As a functional consequence of C3-IgG interaction, C3 binding was found to inhibit the specific precipitation of an IgG antibody preparation.

Possible mechanisms of the first step of the classical complement activation pathway: binding and activation of C1

Different immunoglobulin preparations of human monoclonal IgM, normal human and rat IgG, as well as purified rabbit antibodies were treated by various methods, fragmentation, aggregation and complexing with antigen. The ability of the treated and untreated preparations to fix isolated human C1, to activate the classical complement pathway (to consume C4 in normal human serum) were compared. It was found that the different methods affected the conformation of the immunoglobulin molecules in different ways and induced changes to a greater or lesser extent in the two capacities of the preparations tested. In the case of the monoclonal IgM preparation a strong C1-fixation was observed without measurable complement activation. Other preparations, interfacially aggregated human IgG, BSA-anti-BSA and OA-anti-OA immune complexes had a very weak C1-fixing but a marked complement activating capacity. Some preparations, e.g. heat-aggregated IgG, both fixed and activated C1 effectively, aggregates with a complement-activating capacity without C1-fixing effect were separated by gel-filtration. It was demonstrated further, that at a given time only a part of the activated C1 molecules could be found fixed to the immunoglobulins, the other part was released into the fluid phase after activation. On the basis of the results of this and previous studies a hypothesis is proposed suggesting three possible results of the interaction between C1 and the different preparations: (1) firm fixation and activation; (2) binding not followed by activation and (3) a transient binding leading to activation. The possible application of this hypothesis for the interpretation of the results of the different methods for detecting immune complexes is discussed.

Factors influencing the in vitro interaction between immunoglobulins and isolated C1: a critical study

The C1 fixation test is widely used for the study of the interaction between immunoglobulins, their fragments and the complement system. Some factors influencing the apparent extent of the C1 fixation ability of immunoglobulins and immunoglobulin fragments have been studied. C1 preparations purified by two different methods (euglobulin precipitation and affinity chromatography) were used in parallel in the majority of the experiments. It was demonstrated that the haemolytic activity of both types of C1 preparation was considerably decreased during the incubation at 30° for 10 min (first step of the C1 fixation assay) and the C1s-dependent C4 inactivating effect of C1 also was reduced approximately to the same extent. Gelatin, Trasylol (GORDOX®) and 1,4-diaminobutane in low concentration (0.01 M) were shown to cause an increase in the apparent haemolytic activity of C1. This effect was not due to the reduction of the rate of C1 inactivation, nor to the blocking of the adsorption of C1 to the glass vessel walls; but was based on the ability of these compounds to increase the strength of binding between C1 and EAC4 cells. Similarly, the apparent extent of the C1 fixation by immunoglobulin preparations and their fragments was significantly increased in the presence of gelatin. In the absence of gelatin, a dual effect of immunoglobulins on C1 was observed: (1) fixation to the immunoglobulin; (2) reduction of the inactivation of C1 in the presence of immunoglobulins. The significance of these findings to the mechanism of the C1 binding to immunoglobulins is discussed.

The role of interchain disulphide bridges in the conformational stability of human immunoglobulin G1 subclass. Hydrogen-deuterium exchange studies

The hydrogen-deuterium exchange data of human immunoglobulin G1 (IgG1) are interpreted by assuming fast fluctuations of the protein conformation, through which the peptide groups become exposed to the solvent. The probability of solvent exposure of peptide hydrogens reflects a rather loose conformation for native IgG in comparison with other globular proteins. The probability of solvent exposure is greater than 10(-3) for half of the peptide groups, which shows that the conformational transitions by which these groups are exposed to the solvent are accompanied by changes in standard free energy less than 17 kJ/mol (4 kcal/mol). In the range of pH 6.2-8.45, at 25 degrees C no gross conformational changes are reflected in the hydrogen-deuterium exchange behaviour of the native, the reduced-nonalkylated-reassociated and the reduced-S-alkylated-reassociated IgG1. No difference could be detected in the conformational stability of the native and reoxidised reassociated IgG1 proteins. The lack of inter-subunit disulphide bridges in S-alkylated-reassociated molecules results in an increased conformational motility. This destabilization of protein conformation affects about 90% of the peptide groups covered by the measurements, and corresponds to changes in standard free energy of 8 kJ/mol on the average.