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

Site-Specific DBCO Modification of DEC205 Antibody for Polymer Conjugation

The design of multifunctional polymer-based vectors, forming pDNA vaccines, offers great potential in cancer immune therapy. The transfection of dendritic immune cells (DCs) with tumour antigen-encoding pDNA leads to an activation of the immune system to combat tumour cells. In this work, we investigated the chemical attachment of DEC205 antibodies (aDEC205) as DC-targeting structures to polyplexes of P(Lys)-b-P(HPMA). The conjugation of a synthetic block copolymer and a biomacromolecule with various functionalities (aDEC205) requires bioorthogonal techniques to avoid side reactions. Click chemistry and in particular the strain-promoted alkyne-azide cycloaddition (SPAAC) can provide the required bioorthogonality. With regard to a SPAAC of both components, we firstly synthesized two different azide-containing block copolymers, P(Lys)-b-P(HPMA)-N₃(stat) and P(Lys)-b-P(HPMA)-N₃(end), for pDNA complexation. In addition, the site-specific incorporation of ring-strained dibenzocyclooctyne (DBCO) moieties to the DEC205 antibody was achieved by an enzymatic strategy using bacterial transglutaminase (BTG). The chemical accessibility of DBCO molecules within aDEC205 as well as the accessibility of azide-functionalities on the polyplex’ surface were investigated by various SPAAC experiments and characterized by fluorescence correlation spectroscopy (FCS).

THE ROLE OF DISULFIDE BONDS IN THE COMPLEMENT-FIXING AND PRECIPITATING PROPERTIES OF 7S RABBIT AND SHEEP ANTIBODIES

The number of total disulfide bonds in rabbit and sheep 7S gamma globulin, before and after treatment with 2-mercaptoethanol, has been measured by amperometric titration. Mercaptan reduction could diminish the complement-fixing efficiency of 7S rabbit gamma globulin by no more than 90 per cent without any significant decrease in maximal complement-fixing ability. This was associated with the reduction of only 7 disulfide bonds, including 1 interchain disulfide bond [S—S₍₁₎]. The reduction of 7 disulfide bonds in 7S sheep gamma globulin was associated with a 64 per cent decrease in complement-fixing efficiency, while reduction of 10 to 11 disulfide bonds decreased the complement-fixing efficiency by 90 per cent. Reduction of more disulfide bonds was not associated with any further decrease in complement-fixing efficiency, nor of any decrease in maximal complement-fixing ability. The reduction of more than 10 to 11 disulfide bonds in 7S rabbit and sheep gamma globulins was associated with a decrease in precipitating ability. The disulfide bonds which are more labile to mercaptan reduction appear to be associated with complement-fixing efficiency while the disulfide bonds which are more resistant to mercaptan reduction appear to be associated with precipitating ability. The measurement of interpolypeptide chain disulfide bonds has been discussed. One easily reduced interchain disulfide bond [S—S₍₁₎] appears to be important for the complement-fixing efficiency of 7S rabbit antibody. The integrity of this same bond is essential for the precipitating ability of 5S rabbit antibody and may also be important for its complement-fixing ability.

Human monocytes produce IL-1 and an inhibitor of IL-1 in response to two different signals

Recently, IL-1 inhibitors from urine, monocytes, or monocyte lines have been described. The relationship of these inhibitors to the production, release, and immunological effects of IL-1 is unclear. The present studies were initiated to describe and quantitate the production of IL-1 and a 23 to 45-kDa IL-1 inhibitor from human monocytes in response to certain stimuli using a mouse thymocyte system responsive to IL-1. Zymosan stimulated monocytes to produce IL-1 but not IL-1 inhibitor. Adherent immune complexes, human IgG1-4, and Fc fragments, but not F(ab')2, stimulated monocyte production of IL-1 inhibitor and little if any IL-1. Fibronectin and three of its fragments had neither effect. These observations suggest that monocytes produce IL-1 or IL-1 inhibitor in response to two different signals, through "endotoxin or beta-glucan" and Fc receptors, respectively. The inhibitor decreases IL-1-induced CD-1, C3H/HeJ, and D10 G4.1 cells but not IL-2-induced CD-1, C3H/HeJ, or CTLL-2 proliferation. The inhibitor competitively blocked binding of radiolabeled rIL-1 to the IL-1 receptor on murine thymoma cells. Preincubation of thymocytes with the inhibitor prevented IL-1-induced proliferation; however, this effect was reversed by washing thymocytes and inhibitor activity was markedly reduced when added 24 hr after stimulation with IL-1. These observations suggest that the inhibitor acts on IL-1 receptors to prevent thymocyte proliferation. Monocytes from patients with systemic lupus erythematosus produced less IL-1 inhibitor than cells from normal volunteers. The decrease in IL-1 inhibitor production may play a role in disease states.

The biological properties of immunoglobulin G and its split products [F(ab')2 and Fab]

Antibodies of the IgG class possess antibacterial, antiviral and toxin neutralizing properties and for this reason are administered prophylactically and therapeutically. In the case of the immunoglobulin preparations commercially available for i.v. application a basic distinction must be made between unsplit immunoglobulins and those antibody preparations obtained by enzymatic digestion, such as F(ab')2 or Fab antibodies. This survey deals with the largely experimental evidence describing the biological properties of these preparations. Administration of antibodies in the presence of the corresponding antigens leads to the formation of immune complexes in the organism. These immune complexes can activate, either directly or indirectly, the cellular and humoral systems which are involved in phagocytosis and the elimination of antigens, in the regulation of the body's own antibody production and in inflammatory reactions. As a result of their inability to interact with Fc receptors, immune complexes with F(ab')2 or F(ab) antibodies appear to be less active in the release of inflammation mediators from leucocytes and thrombocytes than immune complexes with unsplit immunoglobulins. These, on the other hand, can antigen-specifically and non-antigen-specifically suppress the immune system which is not the case for immune complexes with F(ab')2 or Fab antibodies. There are indications that these split products also occur in vivo due to the action of tissue and leucocyte proteases. Unlike Fab preparations, F(ab')2 antibodies have antibacterial and antiviral potencies similar to unsplit immunoglobulins, which is probably due to the ability of F(ab')2 molecules to activate complement, not by the classical but by the alternative pathway. Like Fab preparations, F(ab')2 molecules appear to be superior to unsplit IgG in the elimination of haptens. On account of the relatively long period of time unsplit immunoglobulins remain in the blood, they are well suited for prophylactic treatment and substitution over longer periods. The extent to which indications, obtained predominantly from experimental studies, of a reduced release of inflammation mediators, a lack of immune suppression and a lack of augmentation of IgG catabolism would advocate the use of F(ab')2 split products, especially for therapeutic purposes, can only be ascertained after prospective and comparative studies have been carried out.

In-vivo phagocytosis: enhancement of bacterial clearance by native and enzyme-treated immunoglobulins

The enhancement of bacterial blood clearance in mice by native and enzymatically derived fractions of rabbit anti-E. coli hyperimmune serum was tested. Native immune serum, the corresponding IgG, F(ab')2 and Facb fractions strongly augmented the phagocytosis rate of bacteria, whereas Fab/Fc, Fab, Fc fragments, corresponding preparations from normal serum, and E. coli-absorbed preparations showed no marked enhancing capacity. In one experiment opsonization by IgM was demonstrable. Mice that were injected with fatal doses of bacteria could be protected by subsequent treatment with IgG or F(ab')2 preparations of rabbit anti-E. coli serum. Conclusion is drawn that the Fc region of the IgG molecule is not predominantly responsible for opsonized clearance while the intact divalent antigen cross-linking F(ab')2 fragment - presumably by virtue of complement activation via the alternate pathway - could mediate enhanced bacterial clearance.

Importance of the integrity of the inter-heavy-chain disulphide bond of rabbit IgG in the activation of the alternative pathway of human complement by the F(ab')2 region of rabbit IgG antibody in immune aggregates

Immune aggregates formed from either rabbit IgG antibody or F(ab')2 antibody, and antigen, caused exactly the same extent of incubated with human serum under conditions when incubated with human serum under conditions allowing only alternative pathway activation. These observations confirm that the F(ab')2 region of the antibody molecule can cause alternative pathway activation and that this activation is not affected by the presence of the Fc region of the molecule when only alternative pathway activation is permitted. Under conditions allowing activation of both the classical and alternative pathways, increased alternative pathway activation was obtained with IgG antibody aggregates compared to that obtained with F(ab')2 antibody aggregates. On reduction and alkylation of principally he inter-heavy-chain disulphide bond in the IgG antibody, prior to aggregate formation, it was found that no activation of the alternative pathway by IgG aggregates took place under conditions allowing only alternative pathway activation. Treatment of the IgG antibody with reducing agent alone, or alkylating reagent alone, followed by dialysis and aggregate formation, yielded aggregates which caused alternative pathway activation values close to those obtained for untreated IgG aggregates. These results indicate that the integrity of the inter-heavy-chain disulphide bond of rabbit IgG antibody in immune aggregates is necessary to allow the F(ab')2 region of the IgG molecule to activate the alternative pathway of human complement.

Binding affinity of human autoantibodies: studies of cryoglobulin IgM rheumatoid factors and IgG autoantibodies to albumin

The binding affinity of cryoglobulin IgM rheumatoid factors (RF) for human IgG and of human IgG anti-albumin autoantibodies for HSA was measured by the molecular sieving technique. The binding affinities of the two autoantibodies were consistently low (10(4)-10(5) 1/M) as compared to the affinities of corresponding hyperimmune animal antibodies (10(6)-10(8) 1/M). The findings were discussed in relation to theories on human autoimmunity. The existence of strict autotolerance at the T cell level and of autoreactivity at the low affinity B cell level was considered to be best compatible with the findings of this study and with the major known facts of autoimmunity.

Modification of antityphus antibodies on passage through the gut of the human body louse with discussion of some epidemiologic and evolutionary implications

Evidence is presented to indicate that proteolytic and perhaps other enzymes of the louse midgut, essential to the nutrition of the louse, perform molecular dissection on the antirickettsial antibodies present in the blood of a typhus-immune host that selectively destroys, along with other functions, the portion of the antibody that determines the only known function by which antirickettsial antibodies may operate in host defense mechanisms, namely, opsonization of rickettsiae for enhanced ingestion by professional phagocytes and subsequent destruction. The epidemiologic significance of these findings is discussed in relation to the progressive destruction of cells that produce digestive enzymes of the louse midgut that occurs with progressive rickettsial infection, and the possibility of a negative feedback mechanism in transmission is introduced. Speculations that involve evolutionary concepts of both convergent and divergent varieties with respect to rickettsiae, potentially operational in a system that consists of an obligate blood-sucking arthropod vector and a vertebrate host capable of adaptive responses to both vector and rickettsial agent, are presented.

Immunological properties of isolated IgG and IgM anti-gamma-globulins (rheumatoid factors)

Anti-gamma-globulins of the IgG and IgM classes have been isolated from sera of normal individuals and from patients with osteoarthritis, rheumatoid arthritis and juvenile rheumatoid arthritis. All of the isolated antibodies gave precipitin curves with heat-aggregated, reduced and alkylated gamma-globulin. IgM anti-gamma-globulins gave a positive latex fixation test at 4°C and 37°C while IgG anti-gamma-globulins generally gave a positive test only at 4°C. Anti-gamma-globulins from normals did not fix complement but IgG and IgM anti-gamma-globulins from rheumatoids fixed complement to a similar degree. This in vitro complement fixation could account at least in part for the diminished complement levels seen in many rheumatoid synovial effusions.

Evidence for immune complexes containing antibody to the pepsin site of IgG in rheumatoid synovial fluids

In seventy cases of rheumatoid arthritis, the synovial fluid to serum ratio for the titre of pepsin agglutinator, i.e. the antibody to the pepsin site of IgG, was studied. This was compared with the corresponding ratio for another antibody of the same immunoglobulin class and for other proteins. By this method there was evidence for local production of pepsin agglutinator in two cases and for local inhibition in two other cases. Density gradient ultracentrifugation, performed at pH 7·4 and 3·0, suggested that pepsin agglutinator in immune complexes was present in most of the synovial fluids containing this antibody. Complexes of pepsin agglutinator and F(ab')₂ IgG, prepared in vitro, appeared to fix only small amounts of human complement. Neither did fixation of pepsin agglutinator to immune precipitates increase their complement binding activity.

Complement fixation by the F(ab')2-fragment of pepsin-treated rabbit antibody

The F(ab′)₂-fragments of rabbit anti-ovalbumin and anti-human serum albumin IgG fixed between 30 and 50 per cent of guinea-pig complement when they were aggregated with the appropriate antigen. The fixation took place at 37° but not at 4° and was completely inhibited by 0.005 M EDTA. The fixation was more efficient when preformed immune aggregates were used rather than allowing the aggregates to form in the fixation mixture. The loss in haemolytic activity was probably due to the fixation of one or more of the late components (C3 to C9) of guinea-pig complement since no significant fixation of the C1 and C2 components could be found. These results may help to explain previous conflicting reports on the ability of 5S antibody to fix complement. The results also suggest that rabbit antibody F(ab′)₂ may fix complement by a pathway which utilizes only the components C3 to C9 thus bypassing the more usual pathway initiated by C1 activation.

Activation and inhibition of IgG mediated complement fixation by staphylococcal protein A

Staphylococcal protein A, when added to fresh human, guinea-pig, dog or pig serum, caused a marked depletion of complement. This complement consumption, further studied in the human system, was noted only in γglobulin excess. The consumption of individual complement components indicated an activation mechanism similar to the one induced by aggregated human γ-globulin; i.e. a marked depletion of early-acting components. The activation was time- and temperature-dependent. Almost no complement activation was seen using fresh serum from a patient with agammaglobulinaemia. Inhibition of complement activation was noted when protein A was added at equivalence of precipitation or in excess. The dual effect of protein A might be explained by (I) its ability to arrange γ-globulin molecules in a way initiating the complement cascade and (II) inhibition of Fc mediated complement activation by steric hindrance when added in excess. Possible roles of protein A in the pathogenesis of staphylococcal infections are discussed.

Phagocytosis in subacute bacterial endocarditis. Localization of the primary opsonic site to Fc fragment

The opsonic properties of immune gammaG-globulins isolated from patients with chronic septicemic conditions, principally subacute bacterial endocarditis were studied. Opsonic capacity as well as complement-fixing properties of gamma-globulins appeared to be closely associated with integrity of Fc structures. Progressive pepsin digestion of immune gammaG-globulins, as monitored by successive loss of Gm(a) and Gm(b) antigens, abolished opsonic activity. Colostral gammaA, containing agglutinating antibacterial antibodies but no demonstrable complement-fixing activity, was devoid of opsonic capacity. Reduction of gamma-globulin opsonins with 0.01 or 0.1 M mercaptoethanol progressively abolished opsonic activity in parallel with loss of ability of treated gamma-globulins to fix complement with bacteria. Treatment of gamma-globulin opsonins with 0.01 M sodium metaperiodate also produced complete loss of opsonic capacity in parallel with loss of Gm(b) Fc antigens. These findings, together with antiopsonic effects demonstrable with anti-gamma-globulin factors showing primary reactivity with Fc structures, indicate that the opsonic property of immune gamma-globulins requires the participation of structures integral to the Fc region of gamma-globulin.

The in vivo formation and fate of antigen-antibody complexes formed by fragments and polypeptide chains of rabbit gamma-G-antibodies

The in vivo formation and subsequent fate of complexes formed between specific rabbit gammaG-antibody subunits and circulating protein antigens was studied in rabbits and guinea pigs. Subunits obtained from purified antibodies were injected immediately after an injection of antigen, and the elimination from the circulation of either I*-labeled gammaG-subunits or labeled antigen determined. In the absence of antigen, all gammaG-subunits which lack the Fc fragment were rapidly eliminated. In the presence of excess antigen, F (ab')(2), Fab and Fd fragments reacted with antigen and remained in the circulation as complexes which were eliminated at the same rate as the antigen. Fab hybrids containing a specific Fd fragment and a nonspecific L chain similarly reacted with antigen and remained in the circulation complexed to antigen. In contrast, L chains and Fab hybrids containing a specific L chain and a nonspecific Fd fragment did not react with antigen in vivo and were rapidly eliminated in both presence and absence of antigen. H chains remained in the circulation of rabbits in the absence of antigen, however, in the presence of antigen, more H chains which formed complexes with antigen remained in the intravascular space and were rapidly eliminated when the immune elimination of the antigen by the host occurred. Nonspecific H chains were rapidly eliminated from the circulaion of guinea pigs, whereas specific H chains remained in the circulation with the antigen. F (ab')(2) fragments formed complexes with antigen near antibody equivalence and in antibody excess which were rapidly eliminated, however, less effectively than complexes formed near antibody equivalence with intact gammaG. Complexes formed in antibody excess between Fab fragments and H chains remained in the circulation at all concentrations studied and were eliminated at the rate of antigen. The role of the Fc fragment in the immune elimination of antigen-antibody complexes is discussed.

Properties of fragments of human Wassermann antibodies

γG-globulins† from human syphilitic sera when treated with pepsin are still capable of flocculating cardiolipin antigen but lose their ability to fix guinea-pig complement in the presence of antigen.