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

Amino-acid conjugates of the hapten 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone. Synthesis and confirmation of structure

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone (PhOx = CHOEt) was reacted with methylamine, and 2-phenyloxazole-4-carboxylic acid was coupled with methylamine. The spectroscopic properties of the two products were compared in order to confirm that aminolysis of PhOx = CHOEt occurs by displacement of the ethoxy group to give 2-phenyl-4-(substituted-methylene)-5(4H)-oxazolones and not by attack at the oxazolone-carbonyl followed by rearrangement to give 2-phenyloxazole-4-carboxamides. Ten crystalline conjugates were prepared and characterized by reacting PhOx = CHOEt with an excess of unprotected di- and trifunctional amino acid anions followed by purification by washing them with hydrochloric acid.

The IgG2a antibody response to thyroglobulin is linked to the Igh locus in mouse

The IgG-subclass usage by several strains of mice in the response to immunization with mouse thyroglobulin (mTg) was examined in the experimental autoimmune thyroiditis model. While the subclass usage by most mouse strains was similar, the Ighb allotype-bearing mice consistently produced lower IgG2a levels to mTg. Using CBA-Ighb congenic and recombinant inbred strains of mice, the lower level of IgG2a in the Ighb mouse was mapped to the Igh locus. The regulation of IgG2a appeared to be cis controlled, as the CBA x C57BL/6F1 mouse also produced reduced IgG2a of the Ighb (B6) allotype but not of the Ighj (CBA) allotype.

Effect of human IgG1 peptides on the antigen-specific antibody response of mice in vivo

The effect of synthetic peptides--corresponding to the amino acid sequences 289-301 (Y48) and 293-301 (Y91) within the CH-2 domain in the human IgG1 was studied on the oxazolone-specific primary and secondary antibody response isotype distribution and on the sheep erythrocyte (SRBC)-specific primary IgM response. High responder (Balb/c) and low responder (C57Bl/6) mice to oxazolone hapten were treated intraperitoneally with various doses of peptides simultaneously with the first and second contact sensitization. The relative levels of oxazolone-specific IgM, IgG3, IgG1, IgG2a and IgG2b antibodies were determined by a solid phase radioimmunoassay. Y48 and Y91 peptides in a dose range of 10(-5) - 10(-8) M/animal enhanced the oxazolone-specific antibody response. This effect was more striking under suboptimal conditions: using smaller antigen dose for sensitization, cyclophosphamide pretreatment or using genetically low responder mice. SRBC-specific primary IgM response was enhanced by Y91 peptide, Y48 was ineffective.

Isolation and characterization of IgG2a-reactive autoantibodies from influenza virus-infected BALB/c mice

Repeated influenza virus infection induces the production of dominantly IgG2a-type virus-specific antibodies as well as the appearance of IgG2a-reactive autoantibodies in BALB/c mice characterized by low spontaneous rheumatoid factor-type autoantibody production. IgG2a-reactive autoantibody-producing hybridomas could be isolated from the spleen of influenza virus-infected BALB/c mice. The mAb produced by these clones represent not only IgM but also IgG and IgA isotypes and show strong isotype or isoallotype specificity. The common functional property of these autoantibodies is their preferential- and high-affinity binding to complexed, solid-phase-bound or heat-aggregated IgG2a when compared to native soluble or cell-bound IgG2a. The mechanism of induction and the possible biological function of these autoantibodies are discussed in the light of their fine specificity and functional properties.

In vivo manipulation of IgG2a production by isotype-specific autoantibodies

Repeated intranasal infection of Balb/c mice with A/PR/8 influenza virus induced an intense antiviral IgG response dominated by the IgG2a subclass, and accompanied by the appearance of IgG2a reactive autoantibodies. Cells producing IgG2a reactive autoantibodies could then be cloned as hybridomas from the virus infected animals. Monoclonal antibodies produced by selected hybridomas U28, Z26 and Z41 produced IgM-type antibodies with strong specificity for the IgG2a isotype bearing "a" allotypic determinants on the Fc region. These IgG2a specific autoantibodies showed highly preferred binding to solid phase bound or aggregated IgG2a, compared to soluble native IgG2a. Based on these characteristics they were classified as mono-reactive rheumatoid factor (RF)-like autoantibodies. Passive administration of IgM type IgG2a-specific autoantibodies to influenza virus infected animals resulted in a long-term reduction in the secondary antiviral response. This could be demonstrated by decreased virus neutralizing activity of the serum and diminished level of IgG2a-type anti-viral antibodies. A similar effect was observed in Balb/c mice contact sensitized with oxazolone: passive administration of RF-like antibodies resulted in reduced IgG2a response to oxazolone while the level of antibodies belonging to other isotypes was not influenced. These results suggest an isotype-specific regulatory function of these RF-like autoantibodies presumably acting via antigen-antibody complexes.

Structural characteristics influencing the carrier function of synthetic branched polypeptides based on poly[Lys-(DL-Ala)3)]backbone

Effective carrier function of selected representatives of new branched polypeptides covalently coupled with the synthetic monovalent hapten, oxazolone was studied. The effectiveness of oxazolone-synthetic polypeptide conjugates in inducing oxazolone-as well as carrier-specific antibody responses in inbred mice was compared to that of bovine serum albumin (BSA)- and KLH-oxazolone conjugates. The synthetic polypeptides, poly[Lys-(D-Leui-DL-Alam)] (D-LAK), LAK and FAK, as well as the common poly[Lys-(DL-Alam)](AK) core covalently coupled to oxazolone (Ox) induced a T cell-dependent antibody response when repeatedly administered with or without Freund's adjuvant in mice. This was evidenced by: the increasing titer of oxazolone-specific IgG during the course of the memory response; the appearance of all IgG subclasses; the effective oxazolone-specific priming by the conjugates; and the induction of an intense oxazolone- and carrier-specific DTH reaction. Although the oxazolone-specific antibody response was 10-100 times lower than that induced by KLH- or BSA-oxazolone conjugates, it was accompanied by a lower level or no detectable carrier-specific antibody response despite an effective carrier-specific T cell-mediated response. Significant differences were observed between the effectiveness of synthetic polypeptides used as carrier: highest oxazolone-specific antibody titers were observed using the AK, LAK and FAK conjugates. The intensity and specificity of the DTH reaction and antibody response induced by the carrier-oxazolone conjugates suggested that the distinct effectiveness of L- and D-amino acid-containing conjugates (LAK vs D-LAK and FAK vs D-FAK) was dependent on altered B cell recognition of the haptenic group. Circular dichroism (CD) spectra indicating different local orientation of oxazolone, when coupled to L or D side chain-terminating amino acids, support this suggestion.

Antibody responses to hapten in thymectomized mice: extraordinarily pronounced deficiency in IgG1 production

The effect of thymectomy on the production of antibodies was studied by immunizing mice with hapten-carrier conjugates. Antibody responses were analysed with monoclonal antibody-based quantitative isotype-resolving assays. In spite of bone marrow reconstitution, irradiation without thymectomy caused a long-lasting relative deficiency in responsiveness to T-independent antigens. Even when no visible remnants of the thymus could be observed at the autopsy of thymectomized mice, there appeared to be a gradual recovery of antibody-forming capacity within 4 months, as assessed by the response to a T-dependent antigen. Therefore, some of the thymectomized mice had to be regarded as having recovered with respect to the helper T-cell effect. The antibody responses to T-dependent antigens were improved in all isotypes by a functional T-cell system, but the IgG isotypes seemed to benefit more than IgM. The most conspicuous deficit in antibody production in non-recovered thymectomized mice was observed in the T-dependent responses of the IgG1 isotype (2000-fold reduction in contrast to about 50- to 100-fold in IgG2a, IgG2b, and IgG3).

Influence of side-chain-terminating moieties on the conformation of branched polypeptides and their conjugates with 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone

Poly(Lys-(Xi-DL-Alam] polypeptides carrying hydrophilic (X = His, Glu, Lys) or hydrophobic (X = Nle, Ile, Phe) amino acid residues and their conjugates with 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone were synthesized. The conformational properties of carrier polypeptides and conjugates were studied by circular dichroism (CD) spectroscopy in the wavelength regions 190-250 and 310-380 nm, with the emphasis on analysis under near physiological conditions. Based on CD studies, it could be demonstrated that the helix-forming capacity appears to be related to the hydrophobic nature of the branch-terminating amino acid of the branched polypeptides. With respect to carrier function, the presence of a coupled derivative of oxazolone at the side chain termini generally promotes the formation of helical secondary structure. The absolute configuration of the side-chain-terminating amino acids was found to be important for the local orientation of the hapten molecule in the conjugates.

IgG2a restriction of murine antibodies elicited by viral infections

The isotypic distribution of IgG antibodies was determined in the serum of mice after infection with a panel of RNA and DNA viruses representative of 11 different genera. The antiviral response induced by all these viruses showed a striking preponderance of the IgG2a subclass whatever the strain of mice tested or the time elapsed after infection. Together with the predominance of IgG1 in antiprotein and of IgG3 in anticarbohydrate response, this IgG2a restriction of antiviral antibodies strongly suggests the existence of highly specific mechanisms for the regulation of individual subclasses in the mouse.

The immunomodulatory effect of human IgG Fc fragments on the oxazolone-specific immune response of high and low responder mice

Intravenous injection of human IgG Fc fragments in mice resulted in the stimulation or inhibition of an oxazolone-specific antibody response depending on the schedule of Fc fragment injection. High and low responder mice for oxazolone were injected with Fc fragments according to two protocols: either on the day of oxazolone priming, or together with the oxazolone boost, and the isotype composition of oxazolone-specific antibodies was analysed by solid phase radioimmunoassay. We found the primary and secondary anti-oxazolone IgM levels increased in all instances, irrespective of the schedule of Fc fragment treatment. In contrast, the oxazolone-specific IgG production was increased only if Fc fragments were injected at the time of antigen priming. Injection of Fc fragments together with a secondary injection of oxazolone resulted in the inhibition of oxazolone-specific IgG production. Both stimulation and inhibition of oxazolone-specific antibodies were more pronounced in the low responder C57BL/6 mice strain.

The influence of new thymopoietin derivatives on the immune response of inbred mice

The immunomodulatory activities of new synthetic thymopoietin derivates TP4 (Arg-Lys-Asp-Val) and TP3 (Arg-Lys-Asp) have been compared to those of TP5 (Arg-Lys-Asp-Val-Tyr) which exhibits most of the biological activity of the native hormone and probably represents the active site. Both TP4 and TP3 are shown to exert similar immunomodulatory activities to TP5 affecting both humoral and cellular responses. Primary and secondary antibody responses of high responder mice were enhanced whilst the intensity of DTH reactivity was decreased. The effect on humoral immunity was particularly apparent following administration of TP4 or TP3 to mice undergoing primary antibody responses following immunization with sub-optimal doses of antigen or suppression by CY treatment. Administration of peptide(s) elicited DTH responses in mice previously shown to exhibit genetically determined unresponsiveness: in these animals antibody responses were not modulated. The data may be interpreted that the tetra- and tri-peptide representing the N-terminal sequence of TP5 possess immunomodulatory activity which is in many aspects similar to that of TP5. The experimental systems and protocols employed are shown to be appropriate for investigating the effect(s) of potential immunomodulators on humoral and cellular immunity.

Isotype distribution and fine specificity of the antibody response of inbred mouse strains to four compounds belonging to a new group of synthetic branched polypeptides

A new group of synthetic branched polypeptides was developed to initiate a systematic study of the relationships between the chemical structure (charge, size, primary structure, configuration and conformation), the carrier potential and the antigenic properties of these biodegradable and biocompatible macromolecules. This model system has two main advantages over the previously used ones: (i) the side chains grafted to the poly(L-lysine) backbone are composed of about three DL-Ala and a single chain-terminating amino acid with different absolute configuration and/or identity, and (ii) the conformation of these polypeptides is characterized in solution. The size, charge and inside area of the four molecules selected for this study were identical; however, the identity, the absolute configuration of the chain-terminating amino acids (D-Leu, Leu, Phe or D-Phe) and, in consequence, the conformation of the macromolecules were different. The qualitative and quantitative features of the antibody response induced by the four polypeptides were characterized in inbred mouse strains by IgM and IgG type antibody levels, as well as by isotype distribution and fine specificity of antibodies produced during the primary and memory response. The intensity of the memory response and the characteristics of subclass distribution were dependent on the conformation of the branched polypeptides. These molecules carry at least two types of antigenic determinants. One is ordered to the tetrapeptide side chain, the expression of which proved to be inversely correlated with the backbone-originated helix content of the molecules. The other antigenic determinant corresponds to the common inside area of the polypeptides which is less conformation-dependent and therefore common to all four polypeptides.