Purification and properties of anti-Trypanosoma cruzi antibodies isolated from patients with chronic Chagas' disease

Effect of pregnancy and placental factors on the quality of humoral immune response

Asymmetrical IgG molecules are characterised by the presence of a mannose-rich oligosaccharide group in only one of the two Fab fragments, which impairs the corresponding paratope, causing such molecules to behave as univalent antibodies and therefore as antigen blockers [1-3]. During human and murine pregnancy, an increase has been detected in asymmetrical IgG molecules in serum and those bound to the placenta, which normally releases factors capable of modulating the immune response. It thus seemed of interest to investigate the effect of placental culture supernatants (PCS) on in vivo and in vitro synthesis of rat immunoglobulin IgG1, IgG2a, IgG2b and IgG2C, particularly the ratio of symmetrical and asymmetrical molecules in each isotype. The effect of PCS was determined in vivo by means of passive transfer to virgin females and in vitro by analysing the supernatants of spleen cells cultured in the presence of PCS. The results showed that neither pregnancy status nor PCS were capable of modifying serum levels of IgG2a, IgG2b or IgG2c, whereas the level of IgG1 was reduced. When PCS were added to the spleen cells cultures, an in vitro increase was observed in IgG2a, IgG2b and IgG2c production. The separation of symmetrical from asymmetrical IgG molecules was performed by affinity chromatography in Concanavalin A-Sepharose, as such lectin binds high mannose sugars present only in asymmetrical IgG molecules. It is shown that pregnancy and PCS induce an increase in IgG1 and IgG2 molecules asymmetrically glycosylated, capable of binding to ConA-Sepharose. Therefore, the placenta is capable of releasing factors which can regulate the relative proportion of asymmetrical IgG molecules and induce quantitative and qualitative modifications of the in vitro and in vivo produced antibodies.

Paradoxical behavior of asymmetric IgG antibodies

Changes in the quantity and quality of antibodies occur in the course of an immune response. This review describes the physicochemical and biological properties of asymmetric antibodies as well as their functions, beneficial or harmful to the host, according to the nature of the antigen and the particular situation in which they act. Asymmetric antibodies have two paratopes, one of high affinity, with K0 similar to that of symmetric antibodies, and the other one with an affinity for the antigen 100 times lower. Functional univalence is due to steric hindrance present in one of the paratopes by the carbohydrate moiety attached to the Fd fragment of the Fab region, so these antibodies are unable to form large antibody-antigen complexes and cannot trigger reactions, such as complement fixation, phagocytic activity and antigen clearance. When asymmetric IgG antibodies are specific for self-antigens, they prove beneficial for the host by exerting regulatory functions. In allergic manifestations, in autoimmune diseases and especially during pregnancy, despite the fact that the antigens responsible for the process are foreign to the host, they also perform beneficial activity. During pregnancy, the placenta secretes molecules or factors that regulate the synthesis of these antibodies, thus favoring fetal protection.

Blocking anti-Trichinella spiralis antibodies in chronically infected rats

Specific anti-newborn larva antibodies present in the serum of rats chronically infected with Trichinella spiralis were incapable of inducing killing of newborn larvae by activation of normal peritoneal cells. These late antibodies blocked the cytotoxic reaction induced by early antibodies produced a few weeks after infection. Passive transference of late serum to normal mice failed to induce protective immunity against infection by newborn T. spiralis larvae. When late immunoserum was fractionated by gel filtration, blocking activity was found only in the fraction containing IgG subclasses. By indirect immunofluorescence assay and cytotoxic reaction it was shown that blocking antibodies were specific for newborn larvae and could not be adsorbed with muscle larvae. It is concluded that the synthesis of anti-newborn larva antibodies is modulated in the course of a chronic infection: early antibodies developing shortly after infection are cytotoxic, whereas blocking antibodies predominate in the late population. Furthermore, the results suggest that during a chronic infection, resistance to reinfection may be modified.

IgG asymmetric anti-ovalbumin antibodies synthesized by virgin and pregnant rats

A study on the synthesis of asymmetrical IgG molecules 'with no specific activity' and with anti-ovalbumin activity was carried out both in virgin rats and in rats inoculated with ovalbumin and made pregnant by syngeneic and allogeneic males. Before pregnancy, female rats synthesize about 23% of asymmetrical IgG molecules, when the level of these molecules is assessed in total IgG, in anti-ovalbumin IgG and in the supernatant from the adsorption of anti-ovalbumin antibodies. On the other hand, anti-ovalbumin antibodies isolated are predominantly of the symmetrical IgG type; they are also precipitants and effectors of the biological mechanisms that the host operates to preserve pathogenic antigens (bacteria, parasites). In rats pregnant by syngeneic and allogeneic males, the ratio asymmetric/symmetric IgG molecules increases, and the anti-ovalbumin antibodies are mainly of the asymmetrical IgG type, which aid antigen-blocking. Similar results are found in virgin rats, immunized with ovalbumin and intraperitoneally transferred simultaneously with supernatants of placental cultures. These results suggest that, during pregnancy, there is an increase of the IgG asymmetric/symmetric molecule ratio, produced by placental factors, whatever the immunogen specificity may be. Speculations about this fact are presented.

IgG asymmetric molecules with antipaternal activity isolated from sera and placenta of pregnant human

The proportion of symmetric and asymmetric IgG molecules was studied in 10 mothers at delivery. IgG was obtained from peripheral blood and placental blood sera and by elution at 4 M KCl from placenta cell membranes. The percentage of symmetric and asymmetric molecules was determined in the IgG and in their corresponding F(ab')2 fragments by absorption to Con A-Sepharose. The presence of antipaternal antibodies was investigated by IIF and MC tests using paternal lymphocytes. The average percentage of asymetric IgG molecules in the sera was 24.4, which is about double the value of that found in normal subjects. In the IgG eluted from the placenta, the proportion of asymmetric IgG was much higher, averaging 44.4%. Antipaternal antibodies were detected in 5 mothers by IIF and MC and in two mothers only by IIF. In three mothers no antibodies could be detected. It was found that the concentration of antipaternal antibodies was about three times higher in the asymmetric IgG fraction than in the summetric one. Considering the percentage of asymmetric IgG molecules with antipaternal antigen specificity eluted from placenta and the possibility that they function as blocking antibodies, their participation in fetal protection is suggested.

Effect of bovine non-agglutinating antibodies on the blood clearance of 131I-labelled Brucella abortus strain 45/20

Non-agglutinating anti-Brucella abortus S45/20 antibodies were isolated and purified from sera of immunized cattle by means of immunoadsorption and ion-exchange chromatography (DEAE-Sephadex A-50). They corresponded to the IgG1 isotype as shown by immunoelectrophoresis using monospecific anti-IgG1 and anti-bovine gamma globulin sera. These antibodies failed to agglutinate the antigen. They were detected by the anti-bovine gamma globulin test, showing higher titres than those of agglutinating antibodies during the whole period of the experiment. Blood clearance of 131I-S45/20 in mice, was slower in those groups which had received non-agglutinating antibodies than in the control group.

IgG precipitating and non-precipitating antibodies in rabbits repeatedly injected with soluble and particulate antigens

The immune response of precipitating antibodies and non-precipitating antibodies of high affinity (co-precipitating) of the IgG class was analyzed in rabbits repeatedly injected with egg albumin (as a soluble antigen) B. abortus-egg albumin and polymerized egg albumin (as particulate antigens). The results showed that the levels of anti-egg albumin non-precipitating antibodies induced by the soluble antigen were never higher than 10-15% of total antibodies throughout the experimental time. When particulate antigens were injected, the levels of non-precipitating antibodies increased up to 30-70% of the total antibody levels. This phenomenon is related to the way in which the antigen is available to the immune system (particle or aggregated), and is independent of the response induced by the particulate carrier. Components from the cell wall or bacterial membrane that could act as coadjuvants do not participate in this phenomenon. The results obtained seem to indicate that possibly there was a suppression of the synthesis of precipitating antibodies, and this would produce a relative increase in the non-precipitating antibodies.

Analysis and in vivo assay of B. abortus agglutinating and non-agglutinating antibodies

Studies were made of physicochemical and immunochemical characteristics of Brucella abortus agglutinating and non-agglutinating antibodies in the sera of cattle repeatedly injected with living B. abortus (Strain 1119). Both agglutinating and non-agglutinating antibody were shown to be IgG1, and by immunodiffusion against rabbit anti-cattle gamma-globulin, agglutinating antibody gave a precipitation line of identity with that given by non-agglutinating antibody. Whilst agglutinating antibody increased clearance of antigen from the blood of passively protected mice, non-agglutinating antibody did not enhance clearance. Determination of the spleen infection index in mice pre-treated with agglutinating and non-agglutinating antibody showed that in animals passively immunized with non-agglutinating antibody the number of living (infecting) bacteria was approximately 4 times higher than in the case of agglutinating antibody. The possible potentiation of chronic B. abortus infection by non-agglutinating antibody is discussed.